library: the harness keeps the subscribers, and an id belongs to whoever opened it

Three services had each written the same thing and got it three different
ways: input polled the process list to notice a dead subscriber, and only
when someone else subscribed; the power service never noticed at all; the
device manager noticed drivers but not subscribers. The harness owns the
table now, driven by the events a protocol declares — it registers on the
reserved verb, frames each event once, posts to everyone interested without
waiting on any of them, and reclaims a slot when the kernel says its owner
died. Interest masks moved to the envelope, so a subscriber that wants only
mice asks the same way everywhere.

Two consequences the plan had not foreseen. The device manager now hears a
supervised child's death twice, once as its supervisor and once as a
subscriber, so restart backoff counted every crash twice and gave up after
half as many; it retires the id before counting. And the kernel's published
exit table had eight slots for what is now six subscriptions in a plain
boot, so it holds sixteen.

The other half is a hole the design named early and left standing: a
backend handed out a small integer and then honoured it from anyone. A
process that guessed a file's node id read another client's file; a display
layer had no owner at all, so any client could reconfigure or destroy any
layer; a USB device token was never checked against the client that opened
it. Each is now bound to the task that opened it, and a wrong owner gets
exactly what an unknown id gets — the refusal must not become the oracle
the identical answers elsewhere were designed to remove. Closing a file
changed with it: it used to succeed unconditionally, which would have told
a caller which ids existed.

Suite 111/111, with a new case in which one process holds a file and a
layer, hands both ids to a second process, and finds them untouched after
that process has tried everything with them.

build-support/build.zig

@@ -0,0 +1,131 @@
+//! The danos build API (docs/build-packages-plan.md): the one shared recipe
+//! for building a user-space binary. A binary package's build.zig names its
+//! binary and EXACTLY the modules its source imports — the moral equivalent
+//! of a C file's include list — and `userBinary` resolves each name from the
+//! library domain package that exports it. Nothing is pre-wired: an @import
+//! the package did not declare is a compile error, and a domain none of the
+//! imports come from never appears in the package's manifest. The only
+//! implicit dependency is the kernel package, because the shared root shim
+//! (root.zig, user.ld) lives there and itself reaches start + logging.
+//!
+//! Consumers declare this package in their build.zig.zon (as "build-support")
+//! and @import its build.zig from their own build.zig; nothing is compiled
+//! from this package itself — it exports build-time functions only.
+
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    _ = b; // nothing to build: this package exports build-time functions only
+}
+
+/// The freestanding x86-64 target every danos binary (kernel and user) is
+/// built for. SSE2 is part of the x86_64 baseline and UEFI leaves it enabled
+/// at handoff, so we keep it: disabling it forces soft-float and makes the
+/// compiler unable to encode the vector ops that std's formatting/runtime
+/// still emit.
+pub fn freestandingTarget(b: *std.Build) std.Build.ResolvedTarget {
+    return b.resolveTargetQuery(.{
+        .cpu_arch = .x86_64,
+        .os_tag = .freestanding,
+        .abi = .none,
+    });
+}
+
+/// Resolve one imported module by searching the packages this binary DECLARED
+/// in its own build.zig.zon — the C include path made literal: an import can
+/// only be satisfied by a domain the binary claims, and each domain's own
+/// build.zig (its addModule exports) is the single statement of who owns
+/// what. There is no name table here to drift.
+fn moduleFromDeclaredDependencies(b: *std.Build, name: []const u8) *std.Build.Module {
+    for (b.available_deps) |declared| {
+        const dependency = b.dependency(declared[0], .{});
+        if (dependency.builder.modules.get(name)) |module| return module;
+    }
+    @panic(b.fmt(
+        "no declared dependency exports a module named '{s}' — declare the domain that owns it in this package's build.zig.zon",
+        .{name},
+    ));
+}
+
+/// What `userBinary` needs to know about one user binary.
+pub const UserBinaryOptions = struct {
+    name: []const u8,
+    /// The program's own source file — it becomes the `program` module the
+    /// root shim imports; a program only defines `pub fn main`.
+    root_source_file: std.Build.LazyPath,
+    /// Exactly the modules the program's source @imports (directly or through
+    /// its same-directory files) — no more, no less. Order is free; sorted
+    /// reads best. An undeclared @import fails the compile; a name no
+    /// declared domain exports fails the build graph, naming the miss.
+    imports: []const []const u8,
+    /// Built multi-threaded (`single_threaded = false`) so real atomics/TLS
+    /// work — required before a binary may call `Thread.spawn`
+    /// (docs/threading.md). Threads are a deliberate per-binary opt-in.
+    threaded: bool = false,
+};
+
+/// Build one user-space binary the same way for every program (init, the
+/// services, the drivers): freestanding, ReleaseSmall, `.large` code model
+/// (the image base is above 4 GiB — smaller models emit 32-bit relocations
+/// that can't reach), linked with the shared user link script. Pinned to
+/// LLVM + LLD so the script's PHDRS (segment permissions) are authoritative —
+/// the kernel's W^X user-ELF loader requires exact perms.
+///
+/// The compilation root is not the program's own file but the shared shim
+/// (the kernel package's root.zig), which supplies the root declarations
+/// (`main` re-export, panic handler, `_start` pull) so a program only defines
+/// `pub fn main`. The program's file becomes the `program` module the shim
+/// imports; reach it through `programModule` to add per-binary non-library
+/// modules (compile-time options).
+pub fn userBinary(b: *std.Build, options: UserBinaryOptions) *std.Build.Step.Compile {
+    const kernel = b.dependency("kernel", .{});
+    var imports: std.ArrayListUnmanaged(std.Build.Module.Import) = .empty;
+    for (options.imports) |name| {
+        imports.append(b.allocator, .{
+            .name = name,
+            .module = moduleFromDeclaredDependencies(b, name),
+        }) catch @panic("OOM");
+    }
+    // Settings (target, optimize, code model, ...) live on the root module
+    // only; the program module inherits them.
+    const program_module = b.createModule(.{
+        .root_source_file = options.root_source_file,
+        .imports = imports.items,
+    });
+    const exe = b.addExecutable(.{
+        .name = options.name,
+        .root_module = b.createModule(.{
+            .root_source_file = kernel.path("root.zig"),
+            .target = freestandingTarget(b),
+            .optimize = .ReleaseSmall,
+            .code_model = .large,
+            .single_threaded = !options.threaded, // a threaded binary needs real atomics/TLS
+            .sanitize_c = .off,
+            .stack_check = false,
+            .stack_protector = false,
+            // The root shim itself imports only start (_start + panic) and
+            // logging (std_options) — straight from the kernel package, so a
+            // program's own import list stays exactly its own.
+            .imports = &.{
+                .{ .name = "start", .module = kernel.module("start") },
+                .{ .name = "logging", .module = kernel.module("logging") },
+                .{ .name = "program", .module = program_module },
+            },
+        }),
+    });
+    exe.setLinkerScript(kernel.path("user.ld"));
+    exe.entry = .{ .symbol_name = "_start" };
+    exe.image_base = 0x7000_0000_0000;
+    exe.use_llvm = true;
+    exe.use_lld = true;
+    return exe;
+}
+
+/// The `program` module of a binary built by `userBinary` — the module rooted
+/// at the program's own source file. Per-binary non-library modules (an
+/// addOptions build_options) go here, not on the root shim: module imports
+/// are not transitive, so an import added to the root would be invisible to
+/// the program's code.
+pub fn programModule(exe: *std.Build.Step.Compile) *std.Build.Module {
+    return exe.root_module.import_table.get("program").?;
+}

build-support/build.zig.zon

@@ -0,0 +1,8 @@
+.{
+    .name = .build_support,
+    .version = "0.0.0",
+    .fingerprint = 0xad91962994f4be41, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{},
+    .paths = .{""},
+}

build.zig.zon

@@ -32,6 +32,53 @@
     // Once all dependencies are fetched, `zig build` no longer requires
     // internet connectivity.
     .dependencies = .{
+        // The danos build API — the shared user-binary recipe every build file
+        // (root and per-binary packages) consumes (docs/build-packages-plan.md).
+        .@"build-support" = .{ .path = "build-support" },
+        // The library domains, each a package exporting its modules.
+        .kernel = .{ .path = "library/kernel" },
+        .device = .{ .path = "library/device" },
+        .client = .{ .path = "library/client" },
+        .protocol = .{ .path = "library/protocol" },
+        .csv = .{ .path = "library/csv" },
+        .@"xkeyboard-config" = .{ .path = "library/xkeyboard-config" },
+        // Binary packages (phase 2), consumed as artifacts for the boot image.
+        .@"pci-bus" = .{ .path = "system/drivers/pci-bus" },
+        .init = .{ .path = "system/services/init" },
+        .fat = .{ .path = "system/services/fat" },
+        .display = .{ .path = "system/services/display" },
+        .@"display-demo" = .{ .path = "system/services/display-demo" },
+        .@"device-manager" = .{ .path = "system/services/device-manager" },
+        .input = .{ .path = "system/services/input" },
+        .logger = .{ .path = "system/services/logger" },
+        // The discovery pair and the /test fixtures are lazy: only what a
+        // given build actually ships gets its build file loaded and compiled
+        // (-Ddiscovery picks one of the pair; -Dtest-case pulls the fixtures).
+        .acpi = .{ .path = "system/services/acpi", .lazy = true },
+        .fdt = .{ .path = "system/services/fdt", .lazy = true },
+        .@"ps2-bus" = .{ .path = "system/drivers/ps2-bus" },
+        .@"usb-xhci-bus" = .{ .path = "system/drivers/usb-xhci-bus" },
+        .@"usb-hid" = .{ .path = "system/drivers/usb-hid" },
+        .@"usb-storage" = .{ .path = "system/drivers/usb-storage" },
+        .@"virtio-gpu" = .{ .path = "system/drivers/virtio-gpu" },
+        .@"vfs-test" = .{ .path = "test/system/services/vfs-test", .lazy = true },
+        .@"fat-test" = .{ .path = "test/system/services/fat-test", .lazy = true },
+        .@"badge-scope-test" = .{ .path = "test/system/services/badge-scope-test", .lazy = true },
+        .@"shared-memory-server" = .{ .path = "test/system/services/shared-memory-server", .lazy = true },
+        .@"shared-memory-client" = .{ .path = "test/system/services/shared-memory-client", .lazy = true },
+        .@"crash-test" = .{ .path = "test/system/services/crash-test", .lazy = true },
+        .@"device-list" = .{ .path = "test/system/services/device-list", .lazy = true },
+        .@"pci-cap-test" = .{ .path = "test/system/services/pci-cap-test", .lazy = true },
+        .@"iommu-fault-test" = .{ .path = "test/system/services/iommu-fault-test", .lazy = true },
+        .@"input-source" = .{ .path = "test/system/services/input-source", .lazy = true },
+        .@"input-test" = .{ .path = "test/system/services/input-test", .lazy = true },
+        .@"args-echo" = .{ .path = "test/system/services/args-echo", .lazy = true },
+        .@"process-test" = .{ .path = "test/system/services/process-test", .lazy = true },
+        .@"thread-test" = .{ .path = "test/system/services/thread-test", .lazy = true },
+        .@"user-memory-test" = .{ .path = "test/system/services/user-memory-test", .lazy = true },
+        .@"protocol-registry-test" = .{ .path = "test/system/services/protocol-registry-test", .lazy = true },
+        .@"protocol-denied-test" = .{ .path = "test/system/services/protocol-denied-test", .lazy = true },
+        .@"protocol-conformance-test" = .{ .path = "test/system/services/protocol-conformance-test", .lazy = true },
         // See `zig fetch --save <url>` for a command-line interface for adding dependencies.
         //.example = .{
         //    // When updating this field to a new URL, be sure to delete the corresponding
@@ -70,12 +117,5 @@
     // Paths are relative to the build root. Use the empty string (`""`) to refer to
     // the build root itself.
     // A directory listed here means that all files within, recursively, are included.
-    .paths = .{
+    .paths = .{""},
-        "build.zig",
-        "build.zig.zon",
-        "src",
-        // For example...
-        //"LICENSE",
-        //"README.md",
-    },
 }

build/images.zig

@@ -0,0 +1,166 @@
+//! Boot-image assembly (docs/build-packages-plan.md, phase 3): everything
+//! between "here are the built binaries" and "here is a bootable volume".
+//! The FHS-shaped zig-out install tree, the boot manifest, the boot capsule,
+//! the FAT32 USB image (+ its serial-enabled twin for the QEMU run steps),
+//! and the release ISO — with their check steps. The root build.zig decides
+//! WHAT ships (the bundled list); this file owns HOW it becomes an image.
+
+const std = @import("std");
+
+/// One user binary and its FHS home on the boot volume (and in zig-out).
+pub const BundledBinary = struct { path: []const u8, binary: std.Build.LazyPath };
+
+pub const Options = struct {
+    /// The installed/flashable kernel (serial follows the root -Dserial).
+    kernel: *std.Build.Step.Compile,
+    /// The serial-enabled kernel variant the `run-x86-64` image boots.
+    kernel_serial: *std.Build.Step.Compile,
+    /// The UEFI loader (BOOTX64).
+    efi: *std.Build.Step.Compile,
+    /// Every user binary and data file at its FHS path.
+    bundled: []const BundledBinary,
+};
+
+/// Wire up the install tree, both FAT32 boot images, the release ISO, and the
+/// check steps. Returns the serial-enabled FAT image for the QEMU run steps.
+pub fn addImageSteps(b: *std.Build, options: Options) std.Build.LazyPath {
+    // Everything installs into a FHS-shaped zig-out: it IS the danos filesystem *and*
+    // the boot volume. Each binary lands at its addressed, leaf-collapsed path — the
+    // kernel at zig-out/system/kernel (from system/kernel/kernel.zig), init at
+    // zig-out/system/services/init, and so on (see docs/README.md). The bootloader
+    // then loads these FHS paths off the volume.
+    const kernel_install = b.addInstallArtifact(options.kernel, .{ .dest_dir = .{ .override = .{ .custom = "system" } } });
+    b.getInstallStep().dependOn(&kernel_install.step);
+
+    // UEFI firmware requires the removable-media loader at exactly \EFI\BOOT\BOOTX64.efi,
+    // so that path is fixed by the firmware (it is /boot's EFI stub, conceptually).
+    const efi_install = b.addInstallArtifact(options.efi, .{ .dest_dir = .{ .override = .{ .custom = "EFI/BOOT" } } });
+    b.getInstallStep().dependOn(&efi_install.step);
+
+    // The boot manifest: the FHS path of every bundled binary, one per line. The
+    // EFI loader reads THIS by name and opens each listed path by name — FAT
+    // name lookup is case-insensitive and firmware-portable, unlike directory
+    // ENUMERATION, whose returned names vary by firmware (bare 8.3 entries come
+    // back uppercase on some FAT drivers). The tree walk remains only as the
+    // loader's fallback for hand-assembled sticks without a manifest.
+    var manifest_text: std.ArrayListUnmanaged(u8) = .empty;
+    for (options.bundled) |item| {
+        manifest_text.append(b.allocator, '/') catch @panic("OOM");
+        manifest_text.appendSlice(b.allocator, item.path) catch @panic("OOM");
+        manifest_text.append(b.allocator, '\n') catch @panic("OOM");
+    }
+    const manifest_files = b.addWriteFiles();
+    const manifest_file = manifest_files.add("manifest", manifest_text.items);
+    const manifest_install = b.addInstallFileWithDir(manifest_file, .prefix, "system/manifest");
+    b.getInstallStep().dependOn(&manifest_install.step);
+
+    // The boot capsule: the same bundled list packed into ONE file (v2
+    // initial_ramdisk format), because a single open + sequential read is the
+    // only firmware file I/O shape that is fast everywhere — a per-file tree
+    // walk measured MINUTES on real firmware. The loader tries this first,
+    // then the manifest, then the walk; the running system cannot tell the
+    // difference (it always receives the same in-RAM table). Derived from the
+    // tree in the same build graph, so the two cannot drift.
+    const mk_capsule = b.addSystemCommand(&.{"python3"});
+    mk_capsule.addFileArg(b.path("tools/pack-system-image.py"));
+    const capsule_img = mk_capsule.addOutputFileArg("system.img");
+    for (options.bundled) |item| {
+        mk_capsule.addArg(item.path);
+        mk_capsule.addFileArg(item.binary);
+    }
+    const capsule_install = b.addInstallFile(capsule_img, "boot/system.img");
+    b.getInstallStep().dependOn(&capsule_install.step);
+
+    // Install every bundled binary to its FHS home, so zig-out is a true image of
+    // the filesystem — the same tree make-fat-image.py lays out on the boot volume.
+    for (options.bundled) |item| {
+        const install = b.addInstallFileWithDir(item.binary, .prefix, item.path);
+        b.getInstallStep().dependOn(&install.step);
+    }
+
+    // --- danos-usb.img: the bootable FAT32 USB image ---
+    // Format a real FAT32 image (the in-repo Python builder, no external tools)
+    // holding the EFI stub, the kernel, and the whole /system tree of user
+    // binaries at their FHS paths. QEMU presents this image as a USB mass-storage
+    // device the guest boots from (see run-x86-64 and the test harness), and the
+    // danos fat driver mounts the same image at /volumes/usb.
+    const fat_image = addBootImage(b, options.kernel.getEmittedBin(), options.efi.getEmittedBin(), manifest_file, capsule_img, options.bundled);
+    const fat_image_install = b.addInstallFile(fat_image, "danos-usb.img");
+    b.getInstallStep().dependOn(&fat_image_install.step);
+
+    // The image `run-x86-64` boots: identical to the flashable one but with the
+    // serial log sink compiled in, so a developer always gets the machine-readable
+    // log captured to serial0 — without baking serial into the image users flash.
+    // Built lazily (only when `run-x86-64` is requested), and never installed.
+    const fat_image_serial = addBootImage(b, options.kernel_serial.getEmittedBin(), options.efi.getEmittedBin(), manifest_file, capsule_img, options.bundled);
+
+    // `zig build check-fat-image` — validate the produced image is a real FAT32
+    // with the EFI stub present (the builder's own --verify, no external tools).
+    const check_fat = b.addSystemCommand(&.{"python3"});
+    check_fat.addFileArg(b.path("tools/make-fat-image.py"));
+    check_fat.addArg("--verify");
+    check_fat.addFileArg(fat_image);
+    const check_fat_step = b.step("check-fat-image", "Verify the FAT32 USB image is valid and bootable");
+    check_fat_step.dependOn(&check_fat.step);
+
+    // --- release-x86-64: danos-x86-64.iso, the flashable release image ---
+    // Wrap the FAT32 boot volume in a hybrid ISO (the in-repo Python builder
+    // again, no xorriso/isohybrid): an ISO9660 whose El Torito EFI boot entry
+    // and MBR ESP partition entry both point at the embedded FAT image. One
+    // file then boots every way release media is consumed — flashed raw to a
+    // USB stick with Etcher or dd, or burned to optical media — while
+    // danos-usb.img stays the raw superfloppy QEMU and the test harness boot.
+    const mk_iso = b.addSystemCommand(&.{"python3"});
+    mk_iso.addFileArg(b.path("tools/make-iso-image.py"));
+    const iso_image = mk_iso.addOutputFileArg("danos-x86-64.iso");
+    mk_iso.addFileArg(fat_image);
+    const iso_install = b.addInstallFile(iso_image, "danos-x86-64.iso");
+    const release_step = b.step("release-x86-64", "Build the flashable x86-64 release ISO (zig-out/danos-x86-64.iso; flash with Etcher or dd)");
+    release_step.dependOn(&iso_install.step);
+
+    // `zig build check-iso-image` — the ISO builder's own --verify (mirroring
+    // check-fat-image): the MBR partition, the El Torito catalog, and the
+    // embedded FAT32 image must all agree.
+    const check_iso = b.addSystemCommand(&.{"python3"});
+    check_iso.addFileArg(b.path("tools/make-iso-image.py"));
+    check_iso.addArg("--verify");
+    check_iso.addFileArg(iso_image);
+    const check_iso_step = b.step("check-iso-image", "Verify the release ISO is a valid hybrid (MBR ESP partition + El Torito EFI entry)");
+    check_iso_step.dependOn(&check_iso.step);
+
+    return fat_image_serial;
+}
+
+/// Assemble the bootable FAT32 image (the in-repo Python builder) holding the
+/// EFI stub, the kernel, and every user binary at its FHS path — the volume's
+/// /system tree IS the system image; the EFI loader walks it at boot and builds
+/// the in-RAM initial_ramdisk from it. Factored so the serial-enabled
+/// `run-x86-64` variant can bundle its own serial kernel while sharing the
+/// loader and user tree (the loader's boot breadcrumbs and init's heartbeat both
+/// follow the top-level -Dserial). Returns the image's LazyPath.
+fn addBootImage(
+    b: *std.Build,
+    kernel_bin: std.Build.LazyPath,
+    efi_bin: std.Build.LazyPath,
+    manifest: std.Build.LazyPath,
+    capsule: std.Build.LazyPath,
+    bundled: []const BundledBinary,
+) std.Build.LazyPath {
+    const mk_fat = b.addSystemCommand(&.{"python3"});
+    mk_fat.addFileArg(b.path("tools/make-fat-image.py"));
+    const fat_image = mk_fat.addOutputFileArg("danos-usb.img");
+    mk_fat.addArg("64"); // MiB
+    mk_fat.addArg("EFI/BOOT/BOOTX64.efi");
+    mk_fat.addFileArg(efi_bin);
+    mk_fat.addArg("system/kernel");
+    mk_fat.addFileArg(kernel_bin);
+    mk_fat.addArg("system/manifest");
+    mk_fat.addFileArg(manifest);
+    mk_fat.addArg("boot/system.img");
+    mk_fat.addFileArg(capsule);
+    for (bundled) |item| {
+        mk_fat.addArg(item.path);
+        mk_fat.addFileArg(item.binary);
+    }
+    return fat_image;
+}

build/qemu.zig

@@ -0,0 +1,176 @@
+//! The QEMU run steps (docs/build-packages-plan.md, phase 3): `run-x86-64`
+//! boots the serial-enabled FAT image via UEFI/OVMF; `run-x86-64-gpu` adds a
+//! virtio-gpu adapter for the native-present display path. OVMF firmware is
+//! probed across distro/OS layouts (-Dovmf-code / -Dovmf-vars override).
+
+const std = @import("std");
+
+/// Wire up the `run-x86-64` and `run-x86-64-gpu` steps around the given
+/// serial-enabled boot image (the guest boots that self-contained image
+/// attached as USB storage, not the installed FHS zig-out).
+pub fn addRunSteps(b: *std.Build, fat_image_serial: std.Build.LazyPath) void {
+    // Firmware lives in different places per OS/distro, so probe the known
+    // layouts (Architecture, Debian/Ubuntu, Fedora, macOS Homebrew) and use the first
+    // that exists. Override with -Dovmf-code / -Dovmf-vars if yours is elsewhere.
+    const ovmf_code = b.option(
+        []const u8,
+        "ovmf-code",
+        "Path to the OVMF_CODE firmware image",
+    ) orelse firstExisting(b.graph.io, &.{
+        "/usr/share/edk2/x64/OVMF_CODE.4m.fd", // Architecture
+        "/usr/share/OVMF/OVMF_CODE_4M.fd", // Debian/Ubuntu
+        "/usr/share/OVMF/OVMF_CODE.fd", // older Debian/Ubuntu
+        "/usr/share/edk2-ovmf/x64/OVMF_CODE.fd", // Fedora
+        "/opt/homebrew/share/qemu/edk2-x86_64-code.fd", // macOS Homebrew (Apple Silicon)
+        "/usr/local/share/qemu/edk2-x86_64-code.fd", // macOS Homebrew (Intel)
+    });
+    const ovmf_vars = b.option(
+        []const u8,
+        "ovmf-vars",
+        "Path to the OVMF_VARS firmware image (a writable copy is made)",
+    ) orelse firstExisting(b.graph.io, &.{
+        "/usr/share/edk2/x64/OVMF_VARS.4m.fd", // Architecture
+        "/usr/share/OVMF/OVMF_VARS_4M.fd", // Debian/Ubuntu
+        "/usr/share/OVMF/OVMF_VARS.fd", // older Debian/Ubuntu
+        "/usr/share/edk2-ovmf/x64/OVMF_VARS.fd", // Fedora
+        "/opt/homebrew/share/qemu/edk2-i386-vars.fd", // macOS Homebrew (Apple Silicon)
+        "/usr/local/share/qemu/edk2-i386-vars.fd", // macOS Homebrew (Intel)
+    });
+
+    // The firmware needs to write NVRAM, so give it a writable copy of the vars.
+    const vars_copy = b.addSystemCommand(&.{ "cp", "-f", ovmf_vars });
+    const vars_out = vars_copy.addOutputFileArg("OVMF_VARS.4m.fd");
+
+    // Capture the guest's serial0 (danos's machine-readable log) to the qemu-test
+    // scratch area — a dev/host artifact, kept out of the boot volume we mount.
+    // (/system/logs on the volume belongs to the guest's own logger.) One
+    // timestamped file per run.
+    const log_dir = b.fmt("{s}/qemu-test", .{b.install_path});
+    const make_log_dir = b.addSystemCommand(&.{ "mkdir", "-p", log_dir });
+
+    // --- run-x86-64: boot the x86-64 kernel in QEMU via UEFI/OVMF ---
+    const run_efi = b.addSystemCommand(&.{
+        "qemu-system-x86_64",
+        "-device",
+        "qemu-xhci,id=xhci",
+        "-device",
+        "usb-mouse,bus=xhci.0",
+        "-device",
+        "usb-kbd,bus=xhci.0",
+        "-machine",
+        "q35",
+        "-m",
+        "128M",
+        "-drive",
+        b.fmt("if=pflash,format=raw,readonly=on,file={s}", .{ovmf_code}),
+    });
+    run_efi.addArg("-drive");
+    run_efi.addPrefixedFileArg("if=pflash,format=raw,file=", vars_out);
+    // Boot off the FAT32 USB image: a mass-storage device on the same xHCI bus as
+    // the keyboard and mouse. OVMF finds \EFI\BOOT\BOOTX64.efi on it and boots.
+    // The serial-enabled variant, so serial0 carries the log for this dev boot.
+    run_efi.addArg("-drive");
+    run_efi.addPrefixedFileArg("if=none,id=bootusb,format=raw,file=", fat_image_serial);
+    run_efi.addArgs(&.{
+        "-device",
+        "usb-storage,bus=xhci.0,drive=bootusb,removable=on,bootindex=0",
+        "-net",
+        "none",
+        // Emulated display advertising 1280x720 as its native (EDID preferred)
+        // resolution, so the kernel's native-resolution switch has something to
+        // find. `-vga none` avoids a second, default adapter.
+        "-vga",
+        "none",
+        "-device",
+        "VGA,edid=on,xres=1280,yres=720",
+    });
+    const serial_log = b.fmt("{s}/run-x86-64-serial0-{s}.log", .{ log_dir, timestamp(b) });
+    run_efi.addArgs(&.{ "-serial", b.fmt("file:{s}", .{serial_log}) });
+    // We boot the self-contained `fat_image_serial` (added as a file arg above, so
+    // it's already a dependency) — not the installed FHS zig-out — so `run-x86-64`
+    // builds only the serial kernel, never the flashable one. Just make the serial
+    // scratch dir first.
+    run_efi.step.dependOn(&make_log_dir.step);
+
+    const run_efi_step = b.step("run-x86-64", "Boot the x86-64 kernel in QEMU (UEFI/OVMF); serial0 is logged to zig-out/qemu-test/run-x86-64-serial0-<timestamp>.log");
+    run_efi_step.dependOn(&run_efi.step);
+
+    // --- run-x86-64-gpu: the same boot plus a virtio-gpu adapter ---
+    // The VGA device still supplies the boot (GOP) framebuffer the compositor starts
+    // on; the virtio-gpu function is discovered by the device-manager stack, its
+    // driver announces a shared scanout, and the compositor upgrades off the GOP
+    // floor to fenced, tear-free native presents (docs/display-v2.md).
+    // This is the interactive twin of the `display-native` test case, and 512M
+    // matches it (the whole driver stack + the compositor's surfaces at once).
+    // QEMU shows one head per adapter: pick the virtio-gpu head in the View menu
+    // to watch the native output.
+    const run_gpu = b.addSystemCommand(&.{
+        "qemu-system-x86_64",
+        "-device",
+        "qemu-xhci,id=xhci",
+        "-device",
+        "usb-mouse,bus=xhci.0",
+        "-device",
+        "usb-kbd,bus=xhci.0",
+        "-machine",
+        "q35",
+        "-m",
+        "512M",
+        "-drive",
+        b.fmt("if=pflash,format=raw,readonly=on,file={s}", .{ovmf_code}),
+    });
+    run_gpu.addArg("-drive");
+    run_gpu.addPrefixedFileArg("if=pflash,format=raw,file=", vars_out);
+    run_gpu.addArg("-drive");
+    run_gpu.addPrefixedFileArg("if=none,id=bootusb,format=raw,file=", fat_image_serial);
+    run_gpu.addArgs(&.{
+        "-device",
+        "usb-storage,bus=xhci.0,drive=bootusb,removable=on,bootindex=0",
+        "-net",
+        "none",
+        "-vga",
+        "none",
+        "-device",
+        "VGA,edid=on,xres=1280,yres=720",
+        "-device",
+        "virtio-gpu-pci",
+    });
+    const gpu_serial_log = b.fmt("{s}/run-x86-64-gpu-serial0-{s}.log", .{ log_dir, timestamp(b) });
+    run_gpu.addArgs(&.{ "-serial", b.fmt("file:{s}", .{gpu_serial_log}) });
+    run_gpu.step.dependOn(&make_log_dir.step);
+
+    const run_gpu_step = b.step("run-x86-64-gpu", "Boot in QEMU with a virtio-gpu adapter: the compositor upgrades to fenced (tear-free) native presents; watch the virtio-gpu head in QEMU's View menu");
+    run_gpu_step.dependOn(&run_gpu.step);
+}
+
+/// Return the first path in `candidates` that exists on the build host, else the
+/// first candidate as a fallback so a missing-firmware error still names a
+/// concrete (and, by convention, the primary) path. Used to locate OVMF firmware
+/// across distro/OS layouts without configuration.
+fn firstExisting(io: std.Io, candidates: []const []const u8) []const u8 {
+    for (candidates) |path| {
+        std.Io.Dir.accessAbsolute(io, path, .{}) catch continue;
+        return path;
+    }
+    return candidates[0];
+}
+
+/// A UTC timestamp like "20260708-153045", for naming a per-run artifact so
+/// repeated runs don't clobber each other's logs. Resolved when `zig build`
+/// runs, which is moments before QEMU launches.
+fn timestamp(b: *std.Build) []const u8 {
+    const ns = std.Io.Clock.now(.real, b.graph.io).nanoseconds;
+    const secs: u64 = @intCast(@divFloor(ns, std.time.ns_per_s));
+    const es = std.time.epoch.EpochSeconds{ .secs = secs };
+    const yd = es.getEpochDay().calculateYearDay();
+    const md = yd.calculateMonthDay();
+    const ds = es.getDaySeconds();
+    return b.fmt("{d:0>4}{d:0>2}{d:0>2}-{d:0>2}{d:0>2}{d:0>2}", .{
+        yd.year,
+        md.month.numeric(),
+        @as(u32, md.day_index) + 1,
+        ds.getHoursIntoDay(),
+        ds.getMinutesIntoHour(),
+        ds.getSecondsIntoMinute(),
+    });
+}

docs/README.md

@@ -208,7 +208,7 @@ the whole reason for the arrangement ([vision.md](vision.md)).
 danos is a **monorepo of sub-projects**. Each service or driver is a directory that is
 its own Zig module — it can hold as many files as it needs, and other sub-projects
 reach it *by module name*, never by a path into its files. The source tree deliberately
-**mirrors the runtime FHS** ([danos-file-system-hierarchy-FSH.md](file-system-development/danos-file-system-hierarchy-FSH.md)):
+**mirrors the runtime file-system hierarchy** ([file-system-hierarchy.md](file-system-development/file-system-hierarchy.md)):
 what you see under `system/` in the source is what a running danos represents under
 `/system`.
 
@@ -216,7 +216,7 @@ what you see under `system/` in the source is what a running danos represents un
 name.** `system/services/init/` contains `init.zig` (its root), and produces a binary
 addressed as **`system/services/init`** — the repeated leaf resolves away:
 
-| Source (root file)                     | Addressed as (module / binary / FHS path) |
+| Source (root file)                     | Addressed as (module / binary / hierarchy path) |
 |----------------------------------------|--------------------------------------------|
 | `system/services/init/init.zig`        | `system/services/init` → `/system/services/init` |
 | `system/drivers/ps2-bus/ps2-bus.zig`   | `system/drivers/ps2-bus` → `/system/drivers/ps2-bus` |
@@ -263,9 +263,20 @@ test/            → /test      the test tree: the QEMU harness (qemu_test.py, h
   system/services/            beside the on-image test fixtures — vfs-test/ thread-test/
                               crash-test/ … — whose repo path IS their boot-volume path
                               (/test/system/services/<name>)
+build-support/                the danos build API (build-time only, nothing on the image):
+                              the shared user-binary recipe + default-import wiring every
+                              build file consumes (docs/build-packages-plan.md)
+build/                        root-build helpers: image assembly (images.zig) + the QEMU
+                              run steps (qemu.zig)
 tools/                        host-side build scripts
 ```
 
+**Builds are packages** (docs/build-packages-plan.md): each `library/` domain owns a
+`build.zig`/`build.zig.zon` exporting its modules (with a standalone `zig build test`),
+every binary directory is a ~15-line package build, and the root `build.zig`
+orchestrates — the kernel + loader, what ships, and the aggregate test step — with
+image assembly in `build/images.zig` and the QEMU run steps in `build/qemu.zig`.
+
 **Wire protocols live in `library/protocol/`**, one module per directory
 (`library/protocol/vfs/vfs-protocol.zig` is the `vfs-protocol` module), imported by module
 name. A protocol is the seam between a low-level driver and the higher-level service it
@@ -320,5 +331,7 @@ exception in [coding-standards.md](coding-standards.md) applies to that seam.
 | System services (init, the `fat` filesystem, the device-manager) | `system/services/` |
 | Device drivers, one sub-project each (`pci-bus`, `ps2-bus`, `usb-xhci-bus` bus drivers) | `system/drivers/` |
 | On-image test fixtures for the QEMU cases (`vfs-test`, `crash-test`, `thread-test`, …) → `/test/system/services` | `test/system/services/` |
-| Build + `run-x86-64` (QEMU/OVMF) + `release-x86-64` (the flashable ISO) | `build.zig` |
+| Build orchestration (kernel + loader, what ships, the aggregate test step) | `build.zig` (root; the shared user-binary recipe is `build-support/`, and each `library/` domain + binary package carries its own `build.zig`) |
+| Image assembly + `release-x86-64` (the flashable ISO) | `build/images.zig` |
+| `run-x86-64` / `run-x86-64-gpu` (QEMU/OVMF) | `build/qemu.zig` |
 | QEMU integration test harness | `test/qemu_test.py` |

docs/build-packages-plan.md

@@ -0,0 +1,179 @@
+# Plan: packages — hierarchical builds for libraries and binaries
+
+**Status: complete** (branch `claude/build-packages-plan-174144`). Phase 0
+(`build-support`), phase 1 (all six library domains), phase 2 (every binary —
+the pci-bus pilot first, then services, drivers, and test fixtures in waves;
+multi-binary directories like ps2-bus and usb-hid are one package exporting
+several artifacts, and the acpi/fdt discovery pair each export an artifact
+named "discovery" that the root's -Ddiscovery picks between), and phase 3 (the
+root split into `build/images.zig` + `build/qemu.zig`; the root `build.zig` is
+~460 lines of orchestration, down from ~1,250). Every phase landed green: unit
+tests, the QEMU suite at parity with main, boot-image file list unchanged.
+The `lazyDependency` payoff (What-this-buys #4) is in too: the /test fixtures
+and the unselected discovery package are lazy — a build loads and compiles
+only what it ships. And imports are exact: the pre-wired default set is gone;
+every binary names precisely the modules its source imports and carries only
+those domains in its manifest (rule 1 below).
+
+## Why
+
+`build.zig` was ~1,250 lines, growing by three hand-written stanzas per binary;
+at a driver per device family that does not scale. More fundamentally: in one
+monolithic build every binary compiles against library *source*, so a library
+interface break is silently absorbed by whoever edits everything in one commit —
+the interface never has to be honest. danos is about isolation; the build should
+mirror it.
+
+A **package** here is a build-time unit only — a directory owning a `build.zig`
+(recipe: what it exports, how to test it) and a `build.zig.zon` (manifest: name
++ dependencies). Binaries remain fully static freestanding ELFs; packages change
+who declares what, not what links to what. Source code is untouched: `@import`
+uses module names (`"pci"`, `"service"`) exactly as today — only build files
+know where anything lives.
+
+## Target shape
+
+```
+build-support/                 package: the danos build API (userBinary(), defaultImports(), targets)
+library/kernel/                package "kernel":   modules abi, ipc, service, memory, process, logging, time, ...   (depends on protocol)
+library/device/                package "device":   modules driver, pci, usb-abi, model, ...   (depends on kernel, protocol, csv)
+library/protocol/              package "protocol": the wire protocols
+library/client/                package "client"    (depends on kernel, protocol)
+library/csv/                   package "csv"
+library/xkeyboard-config/      package "xkeyboard-config"
+system/services/<name>/        one package per binary: ~15-line build.zig + zon
+system/drivers/<name>/         one package per binary
+build.zig (root)               orchestrator: dependency() per binary, image assembly, QEMU, test steps
+```
+
+The three shared contracts: `boot-handoff` stays a root module (only the
+loader↔kernel pair speaks it); `abi` is exported by the kernel package from
+`../../system/abi.zig` (the source stays with the kernel; userspace's one view
+of it lives in the package, so every consumer names the same module instance);
+`device-abi` is exported by device. Reaching outside the package root means the
+kernel package is valid only as an in-repo path dependency — it could never be
+fetched by hash — which is fine: path dependencies are the only way any of
+these packages is consumed.
+
+Rules:
+
+- **Imports are exact and per binary.** A binary's build.zig names precisely
+  the modules its source `@import`s — the moral equivalent of a C file's
+  include list — and its zon names only the domains those modules come from
+  (plus `build-support` and `kernel`, which is implicit in every binary: the
+  root shim and user link script live there). Nothing is pre-wired: an
+  undeclared `@import` is a compile error, and build-support resolves each
+  name by searching the packages the zon declares — the domains' own
+  addModule exports are the single statement of who owns what, with no name
+  table anywhere to drift. Availability
+  never meant bloat — Zig only compiles what a program actually imports — but
+  exactness makes the declared interface honest and machine-checked.
+- **Modules export source, not artifacts** — each consumer compiles libraries
+  with its own flags, so per-binary optimization choices keep working; Zig's
+  cache deduplicates.
+- **Zon paths are relative and that is accepted.** Binaries sit exactly three
+  levels deep, so the `../../../` prefix is a constant idiom; a library-domain
+  move is a rare, already-breaking event fixed by one sed across manifests, and
+  a stale path fails loudly before anything compiles.
+- **Cross-cutting build changes live in `build-support` only** — that is the
+  contract that keeps per-binary build files declarative.
+
+## What this buys
+
+1. Library interfaces become machine-checked: a consumer can only import what
+   it declared — per binary, down to the single module — and each domain's zon
+   declares what it needs (claim-before-touch, applied to source). A keyboard
+   driver carries `xkeyboard-config` in its manifest; nothing else does.
+2. Each library domain gets a standalone `zig build test` — runtime-library
+   stability testing in isolation.
+3. Adding a binary = adding a directory (source + two small files), not editing
+   three places in a 1,250-line file.
+4. `lazyDependency` lets an image target build only what it ships: the /test
+   fixtures resolve only under -Dtest-case, and only the -Ddiscovery-selected
+   discovery package ever loads.
+
+## Phases
+
+Each phase ends green: `zig build test` passes (88/88 QEMU) and the boot
+image's file list is unchanged. Byte-identical binaries are expected but not
+required (module reorganization can perturb symbol order); file list is the
+hard gate.
+
+**Phase 0 — `build-support`.** Extract `addUserBinary`/`addThreadedUserBinary`,
+the freestanding target setup, and the default-import wiring into the
+`build-support` package. Root build consumes it; nothing else moves. This is
+the cross-cutting-change home, so it lands first.
+
+**Phase 1 — library domains become packages.** In dependency order: `protocol`
+and `csv` (the roots) → `kernel` (depends on protocol: file-system speaks
+vfs-protocol) → `device`, `client`; `xkeyboard-config` stands alone. Each gets
+build.zig + zon + a standalone test step (client's is empty until its modules
+grow host tests — kept for uniformity, since the root aggregate depends on
+every domain's test step). The root build swaps its `createModule` calls for
+`b.dependency("<domain>").module("<name>")`. **No binary moves in this phase**
+— the root build is the pilot consumer, which proves the packages without
+touching 30 binaries.
+
+**Phase 2 — binaries become packages, in waves.** The template was shaken out
+by the pci-bus pilot (see Status). Wave A: services (done). Wave B: the
+remaining drivers (done). Wave C: test fixtures (done). Root build shrank to
+orchestration per wave. init's `-Dserial` heartbeat flag rides a dependency
+option; a directory with several binaries (ps2-bus, usb-hid) is one package
+exporting several artifacts.
+
+**Phase 3 — root cleanup (done).** What remained of the root build split into
+`build/images.zig` (the FHS install tree, boot manifest + capsule, FAT32
+images, release ISO, check steps) and `build/qemu.zig` (the run steps + OVMF
+probing), imported by a short root `build.zig`.
+
+**Afterwards** (outside this plan): the intel-uhd-graphics-750 driver is
+(re)created as a greenfield package. The new-driver checklist's build step
+(docs/device-driver-development/new-driver-checklist.md, step 2) is already
+rewritten against the package template.
+
+## Execution notes (the finished shape)
+
+- The shared recipe lives in `build-support/build.zig`: `userBinary` (what
+  every binary package calls; each named import resolves by searching the
+  packages the binary's zon declares) and `programModule` (for per-binary
+  addOptions modules). The `start` root shim and `user.ld` are named through the kernel
+  package (Dependency.path).
+- Adding a binary = adding a directory with source + a ~15-line build.zig +
+  zon (copy any existing binary package, e.g.
+  `system/drivers/pci-bus/build.zig`) listing exactly the modules the source
+  imports and the domains they come from, then one dependency + one bundled
+  entry in the root build.zig and one zon line.
+- The boot-tree array in the root (search `"etc/init.csv"` or
+  `.getEmittedBin()`) is the image file list — the authoritative comparison
+  target for any future build change.
+- Package unit tests live in each package's own `test` step; the root
+  aggregate depends on every test-bearing package's step, so `zig build test`
+  at the root still runs everything.
+
+Verification per phase:
+
+- Unit tests: `zig build test`.
+- QEMU integration suite: `python3 test/qemu_test.py` (docs/testing.md; the
+  full suite, all cases must pass).
+- Image file list: the boot-tree array is the source of truth — snapshot it
+  (paths only) before phase 0 and diff after each phase; `zig build
+  check-fat-image` must also stay green.
+
+Context a fresh session should read first: this doc, docs/testing.md,
+docs/coding-standards.md (kebab-case names, no abbreviations), and the
+`userBinary`/`userBinaryFromImports` bodies in build-support/build.zig. Commit
+style: no Co-Authored-By trailers.
+
+## Risks / notes
+
+- Zig version churn: the package API (`b.dependency`, zon schema) has moved
+  between releases; the work pins against the repo's current Zig and any
+  upgrade lands separately, never mid-phase.
+- The QEMU size-check tests hardcode source paths (e.g. virtio-gpu protocol
+  struct sizes) — they moved into their binaries' packages with their waves,
+  discharging the carry-along obligation.
+- Doc updates ride each phase: docs/README.md (repo layout + source map),
+  docs/device-driver-development/new-driver-checklist.md (step 2) and
+  devices-csv.md ("Adding a driver"), and the docs that cite the build recipe
+  (driver-model.md, threading.md, system-requirements.md) reference build
+  shapes that keep changing.

docs/c-library-compatibility.md

@@ -0,0 +1,205 @@
+# The C library compatibility layer
+
+A design note and milestone plan for **libdanos-c** — the mini C library that lets
+`zig cc` cross-compile C programs for danos. It is milestone **P0** of
+[python-on-danos-milestones.md](python-on-danos-milestones.md), expanded here the
+way [character-devices-and-tty.md](character-devices-and-tty.md) expands P1.
+CPython is the driving consumer, but the layer is general: any portable C program
+within its surface should build.
+
+## What it is — and the three things it is not
+
+The deliverable is a **sysroot**: a set of C headers plus a static `libdanos-c.a`,
+handed to `zig cc -target x86_64-freestanding-none` via `-isystem` and linked into
+every C binary. Three explicit non-goals keep it small:
+
+- **Not a musl port.** Whole-musl assumes Linux syscall semantics at its bottom
+  (the door the Zig roadmap deferred, twice now). We *lift* musl's pure-computation
+  source files and *write* a danos-native bottom — see the layer split below.
+- **Not full POSIX — *yet*.** Stage 1's surface is "what CPython's minimal
+  configuration and ordinary portable C need" — roughly 100–150 functions — and
+  at that stage absence is a *feature*: configure scripts probe and adapt, and a
+  linker error is honest. But the end state is a **full C compatibility layer**
+  (see "The road to full coverage" below); the absence table is a schedule of
+  arrivals, not a wall.
+- **Not a second runtime.** The library is a thin C-ABI re-spelling of the same
+  danos-native surface `runtime` already provides. It contains no policy of its
+  own; when the Zig track's `runtime.os` seam is authored, the libc bottom
+  re-targets it near-mechanically — the fourth appearance of the roadmap's "same
+  surface" symmetry.
+
+One scoping rule sits above all three — the **size doctrine**: this layer serves
+**applications only**. The kernel and the system services never link libdanos-c;
+they stay danos-native Zig over `runtime`, small and static, because leanness is
+an operating-system property. Applications have their own budget and may be as
+big as they need to be. The libc is how big software *lands on* danos, never how
+danos itself is built.
+
+## The layer split: lift the mathematics, write the plumbing
+
+The realization that makes 100–150 functions tractable: a libc is two very
+different kinds of code, and the hard kind is portable.
+
+| Layer | Contents | Source |
+|-------|----------|--------|
+| **Pure computation** | `string.h`/`memcpy` family, all of libm, `strtod`/`dtoa`, `strtol`, `qsort`, `ctype` tables, `gmtime` calendar math, the `printf`/`scanf` engines, `setjmp` (a dozen instructions of x86-64 asm) | **Lift from musl**, vendored under `library/c/third-party/musl/` (MIT; files compile standalone) |
+| **OS plumbing** | fds (`open`/`read`/`write`/`close`/`lseek`/`stat`/`getcwd`/`chdir`/`isatty`), `mmap`/`munmap`, clocks, `exit`, `getenv`, `getentropy` | **Write in Zig**, exporting C ABI over the `runtime` syscall + VFS client surface |
+| **The middle** | `malloc` over danos `mmap` (simple free-list; CPython's arenas sit above), `FILE*` buffering, `errno` | **Write in Zig** (small, danos-shaped) |
+| **Entry** | `crt0`: the existing danos entry shim ([sysv.md](os-development/sysv.md)) bridged to C `main(argc, argv, envp)`, `environ` initialised, `exit` flushing stdio | **Write** |
+
+Two liftings deserve their own line because getting them wrong is silent
+corruption rather than a linker error:
+
+- **`strtod`/float formatting.** Python's float `repr` guarantees shortest
+  round-trip; that property lives entirely in these routines. musl's are correct;
+  an improvised one would be subtly wrong for years. Lift, never write.
+- **The stdio engines.** musl's `vfprintf`/`vfscanf` are self-contained around
+  its `FILE` abstraction (function-pointer read/write slots), so the whole
+  formatted-I/O engine lifts too — we implement only the fd-backed slots
+  (`__stdio_write`-shaped) and the buffering glue.
+
+## Header policy
+
+Hand-write the headers as danos's own minimal set rather than importing musl's
+(musl's are entangled with Linux ABI details), borrowing declarations freely.
+Freestanding compiler headers (`stdint.h`, `stddef.h`, `stdarg.h`, `stdbool.h`,
+`float.h`, `limits.h`) come from clang via `zig cc` — do not duplicate them.
+`errno.h` values are the danos errno enum re-spelled with POSIX names; there is no
+Linux numbering to be compatible with, so the enum is the truth.
+
+Deliberate absences, and their planned arrivals — this table is the
+compatibility matrix, and "the road to full coverage" below is the schedule
+that empties it:
+
+| Absent | Arrives with |
+|--------|--------------|
+| `pthread.h` | the post-P5 pthread subset over `thread_spawn`/futex — but see the risk below |
+| real `signal.h` (beyond no-op `signal()`/`raise` stubs) | M17 signals-over-IPC in the libc |
+| `dlfcn.h` | [dynamic-libraries.md](dynamic-libraries.md) D1 |
+| `fork`/`exec*`/`wait*` | P5 exposes danos spawn as `posix_spawn`; `fork` itself never (see below) |
+| `socket.h` | a future networking track |
+| locale beyond `"C"` | stage 3 evaluation (CPython is UTF-8-mode happy without it) |
+| pipes (`pipe()`) | P5 process-control cluster |
+
+## The road to full coverage
+
+The layer grows in three stages; only stage 1 is a current milestone (P0), but
+the stages exist so stage-1 decisions never have to be unmade:
+
+- **Stage 1 — CPython-minimal** (P0, the slicing below): ~100–150 functions,
+  static-only, absences honest.
+- **Stage 2 — the danos-complete layer**: the full hosted C11 standard library,
+  plus every POSIX facility danos semantics support, landing as its enabling
+  milestone lands — pipes and `posix_spawn` at P5, real signals at M17, the
+  pthread subset after P5, `dlfcn.h` at
+  [dynamic-libraries](dynamic-libraries.md) D1, sockets with networking. Stage 2
+  is not one milestone but the standing rule that **every system capability
+  gets its C spelling when it ships**, so the matrix above drains as the OS
+  grows.
+- **Stage 3 — ecosystem grade**: the point where "portable C program" generally
+  means "builds on danos" (autotools-style probing included). Reaching it is
+  mostly stage 2 compounding, plus the long tail (locale, wide-char,
+  `fnmatch`/`glob`/`regex` — the last three lift from musl like the rest). At
+  this stage, re-evaluate hand-grown-vs-musl-port once with real data; the
+  standing recommendation remains danos-native — musl's bottom assumes Linux
+  syscall semantics, and by stage 3 the danos bottom exists and is tested —
+  with musl continuing as the quarry for computation code.
+
+Two boundaries are permanent and worth stating at every stage: **`fork` never
+comes** — danos is a spawn-shaped OS, and `fork`'s address-space-duplication
+semantics are hostile to everything from capabilities to threads; software that
+hard-requires `fork` (not `posix_spawn`) stays off the platform. And the
+**public ABI stays the vDSO + IPC protocols** — a full libc is a compatibility
+*layer*, not a second stable system ABI.
+
+## Milestone slicing
+
+1. **sysroot-skeleton** — layout under `library/c/` (a build package:
+   `include/`, Zig sources, vendored musl subtree); `crt0`; string/mem +
+   `ctype` lifted; a `build.zig` step making C binaries first-class targets.
+   *Test:* a C program using only computation links and runs in QEMU
+   (`c-hello` printing via a raw `write` extern to `debug_write`).
+2. **fd-plumbing** — `errno`; open/read/write/close/lseek/stat/unlink/mkdir/
+   rename over the `runtime` VFS client; `getcwd`/`chdir`/`getenv`/
+   `getentropy` arriving as P1 lands them (stubbed truthfully until then:
+   `getenv` empty, `getentropy` `ENOSYS`). *Test:* QEMU `c-file-io` — create,
+   write, reopen, read back, stat size + mtime through FAT.
+3. **malloc** — free-list allocator over danos `mmap`; `calloc`/`realloc`/
+   `free`; alignment guarantees documented. *Test:* host + QEMU allocator
+   torture (interleaved sizes, realloc growth, alignment asserts).
+4. **stdio** — `FILE*`, buffering modes, the lifted printf/scanf engines wired
+   to the fd slots; `snprintf` family; stdin/stdout/stderr over fd 0/1/2.
+   *Test:* host round-trip suite for format engines (especially `%.17g`
+   float round-trip); QEMU `c-stdio` cooked-line echo once P1's console exists.
+5. **mathematics-and-time** — libm lifted wholesale; `strtod`/`strtol`;
+   `clock_gettime` (monotonic + realtime over `clock`/`wall_clock`);
+   `gmtime`/`mktime`/`strftime` (UTC only — no timezone database);
+   `setjmp`/`longjmp`; `qsort`/`bsearch`; `abort`/`assert`. *Test:* host
+   `strtod`/`dtoa` vectors against known-hard cases; QEMU `c-time` sanity
+   against the wall clock.
+
+Slices 1, 3, 4-host, and 5-host have **no dependency on P1** and can start
+immediately; slice 2 and the QEMU halves interleave with P1 as it lands.
+
+**Exit for the layer as a whole** (= P0's exit): `c-hello` and `c-file-io` green
+in the QEMU suite, and the host-side computation tests green — at which point P2
+(CPython configure) becomes the layer's real integration test.
+
+## Testing strategy: two targets, on purpose
+
+The computation layer is target-independent, so it is unit-tested **on the host**
+(built for the host triple, compared against the host libc's answers —
+thousands of cheap oracle checks for `strtod`, `printf`, libm edge cases). The
+plumbing layer only means anything **on danos**, so it is tested in the QEMU
+suite like every other subsystem. Keeping the split explicit stops the slow-QEMU
+suite from absorbing tests that a host `zig test` runs in milliseconds.
+
+## Risks and gotchas
+
+- **CPython's configure may insist on pthreads.** WASI-class targets build
+  threadless, but verify this *first* in P2 bring-up; the fallback is a
+  truthfully-single-threaded `pthread.h` stub set (create returns `EAGAIN`,
+  mutexes are no-ops — valid when only one thread can exist). Decide from
+  evidence, not assumption.
+- **`long double` is x87 80-bit on x86-64.** musl's libm handles it, but keep
+  CPython away from it (`configure` uses `double` throughout by default);
+  don't hand-write anything touching x87.
+- **errno is a contract, not a convention.** The Zig plumbing must map every
+  `runtime` error to a POSIX name consistently — CPython turns errno into
+  exception types (`FileNotFoundError` is `ENOENT`). One table, tested.
+- **`malloc` alignment**: 16-byte minimum on x86-64 (SSE spills in
+  compiled C). The free-list must guarantee it from day one; retrofitting
+  alignment bugs out of an allocator is misery.
+- **Vendoring discipline.** The musl subtree is lift-only — never edited in
+  place (patches live beside it if ever needed), pinned to one musl release,
+  with the file list documented so a version bump is a re-copy, not an
+  archaeology dig.
+- **stdio buffering vs. crashes.** Buffered stdout + a crashing program eats
+  output — the classic debugging trap. `stderr` stays unbuffered (per C
+  standard) and `exit`/`abort` flush; document that `_exit` does not.
+
+## Decisions needing sign-off
+
+- **Lift-from-musl for all pure computation** (vendored, pinned, unedited) rather
+  than writing or porting whole-musl.
+- **Hand-written danos-native headers**; danos errno values are the numbering.
+- **`library/c/` as a build package** producing both the sysroot and the
+  first-class C-binary build step.
+- The **deliberate-absence table** as the living compatibility matrix, drained
+  by the three-stage road above — with exactly one permanent "never": `fork`.
+- **Full coverage as the end state** (stage 3), reached by the standing rule
+  that every system capability ships with its C spelling — not by a musl port.
+
+## Related
+
+- [python-on-danos-milestones.md](python-on-danos-milestones.md) — this is P0.
+- [dynamic-libraries.md](dynamic-libraries.md) — ships in this sysroot
+  (`dlfcn.h` + the loader) once its D1 lands.
+- [python-on-danos.md](python-on-danos.md) — the design note that scoped the
+  layer.
+- [character-devices-and-tty.md](character-devices-and-tty.md) — P1; supplies
+  the console that makes stdio interactive.
+- [zig-self-hosting.md](zig-self-hosting.md) — the `runtime.os` seam the
+  plumbing layer will re-target when it exists.
+- [os-development/sysv.md](os-development/sysv.md) — the entry stack `crt0`
+  bridges.

docs/character-devices-and-tty.md

@@ -0,0 +1,174 @@
+# Character devices, the console, and the tty question
+
+A design note for the **stream** half of the device world. danos has block devices
+(the USB storage service behind the FAT mount) but no character devices — and three
+tracks now need them at once: the terminal application, Zig self-hosting Phase 1
+("wire fd 0/1/2 to a console byte stream"), and [Python on danos](python-on-danos.md)
+Phase 1. This note settles what a character device *is* on danos before any of those
+tracks build one.
+
+## The Unix picture, briefly
+
+Unix splits devices in two: **block devices** are seekable arrays of fixed-size
+sectors (disks); **character devices** are unseekable byte streams (keyboards,
+serial ports, terminals, `/dev/null`, entropy). A **tty** is the canonical
+character device — a byte stream plus a *line discipline* (echo, line buffering,
+erase handling, Ctrl-C-to-signal) that lives in the kernel. A **pty** is a pair of
+character devices (master/slave) that exists so a *userspace* program — a terminal
+emulator — can impersonate terminal hardware to the kernel's in-kernel line
+discipline.
+
+The identification asked for and confirmed: yes, tty and pty are character
+devices in this taxonomy.
+
+## The realization that shapes everything: danos already has the mechanism
+
+A Unix character device is an in-kernel dispatch table: major/minor numbers route
+`read()`/`write()` to a driver. danos already has exactly that dispatch — the VFS:
+`fs_resolve` routes a path to a mounted backend service, and `Operation.mount`
+attaches a backend *endpoint* at a prefix. What is missing is not a device model;
+it is **one node kind with stream semantics**. And the protocol already reserved
+it: `NodeKind.character_device = 2` sits unimplemented in
+[vfs-protocol.zig](../library/protocol/vfs/vfs-protocol.zig), exactly like
+`symbolic_link`.
+
+So the design is small:
+
+**A character device on danos is a VFS node, served by an ordinary service over
+the existing VFS wire protocol, whose read/write have stream semantics.**
+
+No device numbers, no `/dev` special casing, no new syscalls, no new protocol —
+a service is reachable at a path, clients open it with `runtime.fs` like any
+file, and the node kind says what it is. (Since the protocol namespace landed
+in design, that path is `/protocol/console` — a protocol node, see
+[os-development/protocol-namespace.md](os-development/protocol-namespace.md) —
+rather than a mounted device file; the stream semantics below are unchanged.)
+
+### Stream semantics (the actual contract change)
+
+For a node whose kind is `character_device`:
+
+- **`offset` is ignored** on read and write; there is no seek position. (`lseek`,
+  when the C layer exists, returns `ESPIPE`.)
+- **Reads block** until at least one byte is available, then return what is there —
+  **short reads are normal**, not EOF. A zero-length read reply means the stream
+  is closed (hangup), not end-of-file-at-size.
+- **`FileStatus.size` is 0** and means nothing; `mtime` may be 0.
+- Writes may be short if the service's buffer is full; the client loops as it
+  already must for the 256-byte message cap.
+
+This is a semantics note on existing operations, not a wire change — the `Request`
+and `Reply` structs are untouched. The one true protocol addition is a **`control`
+operation** (appended to `Operation`, values stable): a typed request the stream's
+service interprets. Deliberately *not* an `ioctl` grab-bag — the control payloads
+are enumerated per protocol, starting with the terminal set below.
+
+## The first character device is a pseudo-device
+
+The first device is deliberately **not hardware**: an in-memory **loopback** — a
+byte queue served over the stream contract, where bytes written to one end are
+read from the other. It is the reference implementation of the semantics above
+(blocking reads, short reads, hangup on close, the `control` round-trip), it
+tests deterministically with no QEMU serial scripting, and it keeps hardware off
+the critical path entirely. `null` and `zero` come along nearly for free as
+degenerate cases. This is a decision, not a convenience: the dead-COM1 boot bug
+on real hardware already proved serial cannot be assumed present or alive, so
+**nothing in this milestone writes to COM1**. (A serial-backed stream node can
+exist *later* as one more optional backend for headless debugging; it is on
+nobody's critical path.)
+
+The loopback is also not throwaway — it is the seed of P5's `pipe()`, which is
+the same object with two fds.
+
+## The console service
+
+A `console` service owns the line discipline — **in userspace**, where a
+microkernel wants it, not in the kernel as Unix has it:
+
+- **The discipline is a pure library first**: bytes and key events in, bytes
+  out, no I/O of its own — developed and host-tested against in-memory buffers,
+  then shared verbatim between the console and the future terminal application.
+- **Input**: subscribes to keyboard `InputEvent` IPC (the structured events that
+  exist today) and cooks them into bytes. Cooked mode is the default: echo, line
+  buffering, backspace/erase, so a line is delivered on Enter. Raw mode delivers
+  bytes as they come (the REPL's line editor and any full-screen program need it).
+- **Output is a pluggable sink**, and the stream contract is independent of it:
+  the bring-up sink is in-memory (readable back by tests, mirrored to the boot
+  log), and the real one is the framebuffer text renderer when the display
+  track's font work lands.
+- **Control set** (the `control` payloads): mode raw/cooked, echo on/off, and
+  window-size query — the minimal termios. Ctrl-C-to-signal joins when M17
+  signals-over-IPC lands; until then Ctrl-C is just a byte.
+- Mounts itself at `/device/console` as a `character_device` node.
+
+**fd 0/1/2** then stop being special: spawn hands the child three open handles
+(console by default; anything else if the parent chooses), and `runtime`'s fd
+table maps 0/1/2 to them. `isatty` is simply "does `status` say
+`character_device`" — no side channel needed.
+
+## The pty answer: there is no pty
+
+The pty exists in Unix *because the line discipline is in the kernel* — userspace
+terminal emulators need a kernel gadget to impersonate hardware. On danos the
+terminal emulator is already a userspace server, so the pair collapses:
+
+**The graphical terminal application serves the VFS stream protocol itself and
+hands its own endpoints to the children it spawns as their fd 0/1/2.**
+
+The terminal *is* the console service for its children — same protocol, same
+control set, same line discipline code (shared as a library with the boot
+console). No master/slave device pair, no `/dev/pts`, no new kernel object. When
+CPython arrives, the libc's `isatty`/read/write see a character device and are
+none the wiser; when xonsh eventually wants job control, that lands as control
+messages + M17 signals, still with no pty object.
+
+What this costs: programs that *specifically* manipulate Unix ptys
+(`os.openpty()`, `pexpect`-style tools) have no direct equivalent — the danos
+answer is "spawn the child yourself with your own stream endpoints," which is the
+same capability with less machinery. Accepted.
+
+## Milestone slicing
+
+1. **pseudo-devices** — VFS honors `character_device` semantics end to end;
+   `Operation.control` added; the in-memory **loopback** (plus `null`/`zero`)
+   as the first device. QEMU test: one client writes, another reads — open,
+   offsetless read/write, blocking read, short read, hangup on close, control
+   round-trip. No hardware anywhere.
+2. **console-service** — the line-discipline library (host-tested, pure) plus
+   the console composing keyboard `InputEvent`s with an in-memory output sink;
+   mounted at `/device/console`. QEMU test injects key events and reads cooked
+   lines and raw bytes back through the sink.
+3. **fd-inheritance** — spawn passes 0/1/2 handles; `runtime` fd table; `isatty`
+   via `status`; existing binaries' stdout migrates from `debug_write` to fd 1
+   (the logger keeps its own path).
+4. **terminal-as-server** — deferred to the terminal application milestone
+   (Python track P3): the terminal reuses the discipline library and serves its
+   children directly.
+
+Steps 1–3 are exactly the shared seam that Zig self-hosting Phase 1 and Python
+Phase 1 both list; neither track repeats them.
+
+## Decisions needing sign-off
+
+- **No pty object; the terminal serves its children directly** (the section
+  above) — the load-bearing simplification.
+- **`control` as an enumerated, typed operation** rather than an ioctl-style
+  opaque pass-through.
+- **Line discipline in userspace services** (console + terminal, shared library),
+  never in the kernel.
+
+## Related
+
+- [python-on-danos.md](python-on-danos.md) — consumes this as its Phase 1.
+- [zig-self-hosting.md](zig-self-hosting.md) — ditto ("stdio as fds").
+- [file-system-development/vfs-protocol.md](file-system-development/vfs-protocol.md) —
+  the wire protocol this note extends.
+- [file-system-development/file-system-hierarchy.md](file-system-development/file-system-hierarchy.md)
+  — the tree the console surfaces in.
+- [os-development/protocol-namespace.md](os-development/protocol-namespace.md) —
+  supersedes this note's device-node naming: the console lands as a protocol
+  (`/protocol/console`, a protocol node), not a `/dev`-style device file. The
+  stream semantics designed here (line discipline, cooked/raw modes) carry over
+  unchanged.
+- [device-driver-development/input.md](device-driver-development/input.md) — the
+  `InputEvent` stream the console cooks.

docs/device-driver-development/device-manager.md

@@ -64,19 +64,48 @@ restarted instance to rebuild exactly the same ids.
 
 ## The protocol
 
-A `device-manager-protocol` module (the vfs-protocol pattern): extern-struct
+A `device-manager-protocol` module, defined through the
-messages, a version in the handshake, reserved fields everywhere. The manager is a
+[envelope](../os-development/protocol-namespace.md): every packet — request,
-well-known endpoint (`ipc.register(.device_manager)`); the badge tells it who is
+reply, and pushed event alike — begins with the folded `Header`, and **the device
+id is `Header.target`**, the manager's object addressing. The contract is bound at
+`/protocol/device-manager`; the kernel-stamped badge tells the manager who is
 talking; the same endpoint receives its children's exit notifications — one loop,
 one world.
 
-| Direction | Message | Purpose |
+| Direction | Packet | Purpose |
 |---|---|---|
-| driver → manager | `hello { version, role, device_id }` | confirms the argv assignment, starts the deadline clock |
+| driver → manager | `hello { role, version }` @ the assigned device | confirms the argv assignment, starts the deadline clock |
-| bus → manager | `child_added { parent, bus_address, identity, device_id, hid }` | one node the bus discovered |
+| bus → manager | `child_added { parent, bus_address, identity, bus, vendor, device, subsystem, hid }` @ the registered device id | one node the bus discovered |
 | bus → manager | `child_removed { parent, bus_address }` | unplug, or the bus lost it |
-| app → manager | `enumerate` | snapshot of the tree (read-only) |
+| app → manager | `enumerate` (reserved verb 1) | snapshot of the tree: one `ChildEntry` per record in the reply's tail |
-| app → manager | `subscribe` | receive published add/remove events |
+| app → manager | `subscribe` (reserved verb 2) | receive published add/remove events; the subscriber's endpoint rides as the call's capability |
+| manager → app | `child_added` / `child_removed` events | the same two structs, pushed rather than called |
+
+The watcher table behind those last two rows is the **service harness's**
+(`service.Subscribers`, shared with input and power), not the manager's: it
+answers `subscribe`/`unsubscribe`, frames each event once for the fan-out, and
+sweeps a watcher on its exit notification — where the manager previously had no
+sweep for watchers at all. Its own supervised-driver exits are a different thing
+and unchanged, except that a driver's death now arrives twice (the manager is
+both its supervisor and a subscriber to published exits), so the manager retires
+a dead driver's process id as it handles the first and the second finds nothing
+to act on.
+
+Two of what used to be the manager's own operations are the envelope's **reserved**
+verbs, which mean the same thing at every provider in the system, so this protocol
+numbers only three of its own (`hello` = 16, `child_added` = 17,
+`child_removed` = 18) and its two events in their own space (`child_added` = 16,
+`child_removed` = 17). No reply carries a status field: that is the `Status` every
+reply begins with.
+
+`child_added` is the one struct that travels both ways — a bus *calls* it, the
+manager *pushes* it — which is why the operation and event numbering spaces are
+separate: one encoding, both directions, told apart by which way the packet went.
+Folding the operation byte and the device id out of it is also what makes it fit:
+a pushed event is 64 bytes at most, header included, and this one lands exactly on
+that floor. `child_removed` is the single message whose target stays 0, because it
+is addressed by the composite (parent, bus address) and no single `u64` carries a
+pair.
 
 `hello` is the one deadline the manager enforces itself: spawned and silent past the
 deadline means wrong binary, wrong protocol version, or wedged before main — apply

docs/device-driver-development/devices-csv.md

@@ -96,7 +96,15 @@ in different namespaces — against the right `bus` column.
 
 ## Adding a driver
 
-1. Build the driver binary and bundle it at `/system/drivers/<name>` (build.zig).
+(The step-by-step walkthrough with a worked example is
+[new-driver-checklist.md](new-driver-checklist.md).)
+
+1. Create `system/drivers/<name>/` with the driver source plus a ~15-line
+   package `build.zig` + `build.zig.zon` (copy an existing driver package,
+   e.g. `system/drivers/pci-bus/`; per-driver extras go through
+   `build_support.programModule`). Then bundle it at `/system/drivers/<name>`:
+   one dependency + one bundled entry in the root `build.zig`, one line in the
+   root `build.zig.zon`.
 2. Add a row to `etc/devices.csv` naming the identity it binds and its full path.
 
 No device-manager change is required — the registry is the seam.

docs/device-driver-development/display-plan.md

@@ -20,9 +20,10 @@ Read [display.md](display.md) first for the *why*; this is the *what* and the *o
 
 Follow [coding-standards.md](../coding-standards.md): spell out non-acronym abbreviations in
 full, kebab-case file names, no `Co-Authored-By` trailers on commits. New user binaries
-go through `addUserBinary` in [build.zig](../../build.zig) and get packed into the
+go through build-support's shared user-binary recipe and get packed into the
-initial-ramdisk; protocols are `b.addModule("…-protocol", …)` and imported into the
+initial-ramdisk; protocols are modules exported by the `library/protocol` package.
-`runtime` module.
+(This section predates the build-packages split; see
+[build-packages-plan.md](../build-packages-plan.md) for the current build shape.)
 
 ## How to verify along the way
 

docs/device-driver-development/display-v2-plan.md

@@ -18,9 +18,11 @@ lands on its own and ends in a **verifiable gate** — shaped for a `/loop` run,
 
 Follow [coding-standards.md](../coding-standards.md): spell out non-acronym abbreviations,
 kebab-case file names, no `Co-Authored-By` trailers. New user binaries go through
-`addUserBinary` and get packed into the initial-ramdisk; protocols are
+build-support's shared user-binary recipe and get packed into the initial-ramdisk;
-`b.addModule("…-protocol", …)` imported into `runtime`; new syscalls extend
+protocols are modules exported by the `library/protocol` package; new syscalls extend
-[abi.zig](../../system/abi.zig) `SystemCall` + a `library/runtime` wrapper.
+[abi.zig](../../system/abi.zig) `SystemCall` + a `library/kernel` wrapper.
+(This section predates the build-packages split; see
+[build-packages-plan.md](../build-packages-plan.md) for the current build shape.)
 
 ## How to verify along the way
 

docs/device-driver-development/display.md

@@ -29,7 +29,7 @@ which one you're holding decides what you can do.
 
 - **The PCI class-0x03 device is the raw controller** — BARs, config space, registers,
   IO ports. It is what you actually *own* after boot. On QEMU's emulated adapter
-  ([`-device VGA,edid=on`](../../build.zig), the Bochs VBE/DISPI model) the `base` GOP handed
+  ([`-device VGA,edid=on`](../../build/qemu.zig), the Bochs VBE/DISPI model) the `base` GOP handed
   you *is* that device's linear-framebuffer BAR — the same physical memory, seen through
   a different door. On a real discrete GPU, GOP's `base` is an aperture inside the GPU's
   VRAM BAR. danos already decodes this device
@@ -87,13 +87,13 @@ rest of the system hasn't had to face:
      │   (ResourceKind.memory = [base, height*pitch], write-combining hint,
      │    plus DisplayInfo{width, height, pitch, format, refresh_hz})
      ▼
-  display service   (system/services/display/, ServiceId.display)      ← the compositor
+  display service   (system/services/display/, /protocol/display)      ← the compositor
      │   device.claim(display node) → mmio_map(WRITE-COMBINING) = FRONT buffer (the LFB)
      │   mmap(cacheable) a BACK buffer of the same geometry
      │   owns:  an ordered LAYER STACK  +  a per-frame DAMAGE tracker (rect list or tile grid)
      │   loop:  composite dirty layers → back buffer → present dirty rects → front
      │   backend is an INTERNAL interface: {gop-fb} at boot; {virtio-gpu} on hot-attach (v2)
-     ▼   reached by name (ipc_lookup); clients drive it over the display protocol
+     ▼   reached by name (open /protocol/display); clients drive it over the display protocol
   ┌────────────────────────────────────┬──────────────────────────────────────┐
   drawing clients (v1)                  surface clients (deferred)
   display commands:             display surfaces:
@@ -106,8 +106,10 @@ The bring-up sequence mirrors a hardware driver's — it is the
 [`usb-xhci-bus` `initialise`](../../system/drivers/usb-xhci-bus/usb-xhci-bus.zig) shape
 (claim → `mmio_map` → run loop) — and the request/reply service shell is the
 [FAT](../../system/services/fat/fat.zig) / [input](../../system/services/input/input.zig) shape
-([`service.run`](../../library/kernel/service.zig) with a `protocol.zig` of
+([`service.run`](../../library/kernel/service.zig) over the dispatch table its
-`extern struct` messages and an `Operation` tag).
+protocol module generates through
+[`envelope.Define`](../os-development/protocol-namespace.md) — one request and
+reply type per verb, and the layer id in the packet header's `target`).
 
 **One process, for now.** v1 is a *single* service that both owns the framebuffer and
 composites — it does not split a "framebuffer driver" from a "compositor" the way input
@@ -209,6 +211,18 @@ shell, a terminal, a cursor, and a wallpaper:
 | `damage`           | mark a region of a layer dirty                                |
 | `present`          | request a repaint: composited at the next frame-clock tick    |
 
+**A layer belongs to the client that created it.** The id is a slot in a
+sixteen-entry table — small, dense, guessable — so every verb above that names one is
+answered only for the task whose `create_layer` produced it, and a layer that is
+somebody else's is refused exactly as one that never existed (`-ENOENT`), so a client
+cannot use the refusal to learn which ids are live
+([protocol-namespace.md](../os-development/protocol-namespace.md): handles are scoped
+per client, validated against the badge). The compositor's own layers — the cursor
+sprite and the startup self-check's pair — are marked service-owned and are created by
+direct call rather than over the protocol, so no client can move or destroy the
+cursor. A dead client's layers are released on its exit notification, the same sweep
+the FAT server runs for open files.
+
 Text is intentionally *not* an operation — a client renders glyphs by blitting tiles
 (the [PSF font](../../system/kernel/font.psf) path the console already uses can move into a
 client). Keeping the protocol to rectangles and tiles keeps the compositor small and the

docs/device-driver-development/driver-model.md

@@ -138,13 +138,17 @@ a higher-level service (block ↔ filesystem, a scanout driver ↔ the composito
 private wire to its *hardware* — virtio-gpu's command set — is not that; it stays a
 driver-private file, like the virtio-pci transport beside it.
 
-The build side of this has since landed: [`addUserBinary`](build.zig) injects the
+The build side of this has since landed: every binary owns a package whose
-default modules — the library/kernel concern modules (`ipc`, `memory`, `process`, `time`,
+~15-line `build.zig` names EXACTLY the modules its source imports — the moral
-`logging`, `file-system`, `thread`, `service`), the device/service clients (`driver`,
+equivalent of a C file's include list — and the shared recipe in
-`block`, `display`, `input`), plus `mmio`, `xkeyboard-config`, `acpi-ids` — into every user
+[`build-support/build.zig`](../../build-support/build.zig) (`userBinary`)
-binary, and per-binary extras — protocol modules, bus logic — are added with
+resolves each name from the library domain that exports it (kernel's concern
-`programModule(exe).addImport(...)`. That's the *entire* mechanism — Zig modules
+modules, the device driver libraries, the service clients, the protocols). An
-already give you everything else.
+undeclared `@import` is a compile error, and a domain none of the imports come
+from never appears in the binary's manifest — a keyboard driver declares
+`xkeyboard-config`; nothing else does (see
+[build-packages-plan.md](../build-packages-plan.md)). That's the *entire*
+mechanism — Zig modules already give you everything else.
 
 The discipline that makes this work: **a class driver must not import a bus's *hardware*
 logic module.** `usb-hid` imports `usb` (the transfer client) and `input-protocol`, never

docs/device-driver-development/input.md

@@ -22,12 +22,22 @@ event:
 - `JoystickEvent` — `axis` moves (a signed value on a `control` index) and
   `button_down`/`button_up`.
 
-All three travel in one **`InputEvent` envelope** tagged with a `DeviceKind`, so the
+A source publishes any of the three as one **`InputEvent`** tagged with a `DeviceKind`, so
-fan-out is a single code path and a subscriber can take a mix of classes on one stream.
+`publish` is a single verb; decode one with `asKeyboard()` / `asMouse()` / `asJoystick()`
-Decode an envelope with `asKeyboard()` / `asMouse()` / `asJoystick()` (each returns null
+(each returns null unless the tag matches). On the *delivery* wire the class is the
-unless the tag matches). A subscriber names the classes it wants with a **`device_mask`**,
+packet's own operation instead — the protocol declares one event per class
-and the service routes each event only to subscribers whose mask includes its class — so a
+([protocol-namespace.md](../os-development/protocol-namespace.md)), so a pushed packet is
-mouse-only listener never wakes for keystrokes.
+the 16-byte header plus the typed event and nothing carries a tag twice. The client
+helpers re-tag what arrives back into an `InputEvent`, so a subscriber can still take a
+mix of classes on one stream. A subscriber names the classes it wants with a
+**`device_mask`**, and the service routes each event only to subscribers whose mask
+includes its class — so a mouse-only listener never wakes for keystrokes.
+
+**`subscribe` is not this protocol's verb.** Its shape — a synchronous call whose attached
+capability is the subscriber's own endpoint — is what the envelope's *reserved* subscribe
+means at every provider in the system, so the input protocol adopts it rather than
+defining a second spelling of the same thing. The interest mask rides as the packet's
+tail. `publish` is the one verb the protocol defines for itself.
 
 ## Why this needed a new kernel primitive
 
@@ -98,12 +108,25 @@ This is the async counterpart of `ipc_call`, and the input service is its first
   `publishJoystickEvent`. Publishing is a short synchronous `ipc_call` the service answers at
   once; the service's own fan-out is asynchronous, so publishing never blocks on a slow
   subscriber.
-- The **service** ([input.zig](../../system/services/input/input.zig)) keeps a small subscriber
+- The **service** ([input.zig](../../system/services/input/input.zig)) owns none of that
-  table (endpoint handle + owning task id + `device_mask`). On `publish` it `ipc_send`s the
+  machinery any more: the subscriber table (endpoint handle + owning task + interest mask),
-  event to every subscriber whose mask includes the event's device class. On `subscribe` it
+  the reserved `subscribe`/`unsubscribe` verbs, the fan-out, and the dead-subscriber sweep
-  stores the passed capability and mask and, as housekeeping, prunes any slot whose owning
+  are the shared harness's (`service.Subscribers` in
-  process has exited (checked against `process_enumerate`) — not for correctness (an async
+  [service.zig](../../library/kernel/service.zig)), so every event stream in the system has
-  send to an orphaned endpoint is harmless) but to reclaim the slot.
+  identical semantics. What is left in this file is what is actually about input: which
+  class an event belongs to, and which classes a subscriber asked for. On `publish` it names
+  the event's class and the harness `ipc_send`s the packet — framed once — to every
+  subscriber whose mask includes it.
+- **A dead subscriber goes away on its exit notification**, not on a poll. The service used
+  to walk `process_enumerate` on every subscribe and drop slots whose owner had gone; it now
+  subscribes to the kernel's published exits like the FAT server and the compositor do
+  ([process-lifecycle.md](../os-development/process-lifecycle.md)), which reclaims the slot
+  *and* closes the endpoint capability in it promptly rather than at the next subscribe.
+  (The fan-out also drops a subscriber whose `ipc_send` fails, as a backstop for a
+  notification a full ring dropped.)
+- The service runs on the shared harness like every other, so it answers the universal ping
+  and exits on `terminate`; it was the last hand-rolled receive loop in the tree, and the
+  last service a shutdown had to kill rather than ask.
 
 Publisher and subscriber must be **separate processes**: a single thread that both
 published and serviced its own subscription would deadlock (its `publish` call blocks until

docs/device-driver-development/ipc.md

@@ -1,34 +1,70 @@
-# IPC: message-passing channels
+# IPC: the kernel-ipc transport
 
 Inter-process communication is the **backbone of a microkernel**. Once drivers and
 services run isolated in their own address spaces ([vision](../vision.md)), they can't
-just call each other — a request becomes a **message**. In a microkernel, whatever
+just call each other — a request becomes bytes on a wire. In a microkernel, whatever
 was a function call across a monolithic kernel is IPC, so it's a first-class
 concern, not an afterthought.
 
-There are two layers, built a milestone apart:
+This document describes **one transport** — the bottom layer (L0) of the
+communication stack defined in
+[communication.md](../os-development/communication.md), which owns the model
+and the vocabulary (*protocol*, *channel*, *packet*, *signal*, *endpoint*).
+kernel-ipc is the **first** transport, not the only possible one: in
+buffer-plus-doorbell terms it is a kernel-owned mailbox with the scheduler as
+the doorbell. Its distinguishing properties, which the layers above may rely
+on where they say so:
 
-- **`system/kernel/ipc.zig`** — a bounded blocking channel between *kernel threads*,
+- **Rendezvous.** A call is a synchronous meeting, copied sender-page to
-  described below. The primitive, and where the blocking discipline was worked out.
+  receiver-page — natural backpressure, no queue to size.
-- **`system/kernel/ipc-synchronous.zig`** — synchronous call/reply between *processes*, across
+- **Capability carriage.** The *only* transport that can move a handle
-  address spaces. What user-space servers and drivers actually talk over. It's the
+  between processes. Channels are therefore always established over
-  second half of this document.
+  kernel-ipc, and it remains every channel's control path even when bulk
+  data is negotiated onto a fatter transport (a shared-memory ring).
+- **Verified source.** Every delivery carries the kernel-stamped badge — the
+  identity the channel layer attaches to received packets.
+- **Bounded packets.** 256 bytes call/reply, 64 pushed — the floor every
+  protocol may assume on any transport.
 
-## The channel
+Three properties keep the networking analogy honest — kernel-ipc is
+networking-*shaped*, not TCP:
 
-The first form is a **bounded blocking channel** (`system/kernel/ipc.zig`): a fixed-size
+- **Channels over it are RPC-shaped, not streams.** Packets, call/reply,
-ring buffer of messages with a producer/consumer rendezvous, built on the
+  datagram pushes — closer to UDP plus RPC than to a byte stream. Ordering
-scheduler's [wait queues](../os-development/scheduling.md).
+  exists per exchange (a reply answers its call), not across a channel.
+- **Possession is the connection.** There is no handshake state in the
+  kernel: holding the capability *is* having the channel. A provider's one
+  endpoint terminates every client's channel at once, demultiplexed by badge
+  — like every client sharing the server's listening socket, with
+  per-connection state living in the provider, keyed by badge. A *private*
+  channel (a dedicated endpoint pair) is built when wanted: that is exactly
+  what `subscribe` does.
+- **Packets never fragment.** If it doesn't fit in a packet, it isn't a
+  packet: bulk data lives in shared memory and a packet (or signal) is the
+  doorbell. The display path already works this way.
+
+The rest of this document is the implementation, bottom-up: the kernel-thread
+queue the blocking discipline was worked out on, then endpoints — this
+transport's termination points.
+
+## The kernel-thread queue
+
+The first form is a **bounded blocking queue** (`system/kernel/ipc.zig`): a
+fixed-size ring buffer of messages with a producer/consumer rendezvous, built
+on the scheduler's [wait queues](../os-development/scheduling.md). (Its type
+is still named `Channel(T, capacity)` — it predates the vocabulary above, and
+is a *queue between kernel threads in one address space*, not a channel in
+the model's sense; a rename can ride a later flag-day.)
 
 `Channel(T, capacity)` is generic over the message type and buffer size. It holds a
 ring buffer, a count, and two wait queues:
 
-- **`send(msg)`** — if the channel is full, block on the *not-full* queue; otherwise
+- **`send(msg)`** — if the queue is full, block on the *not-full* queue; otherwise
   write the message, bump the count, and wake a waiting receiver.
-- **`receive()`** — if the channel is empty, block on the *not-empty* queue; otherwise
+- **`receive()`** — if the queue is empty, block on the *not-empty* queue; otherwise
   take a message, drop the count, and wake a waiting sender.
 
-Neither side busy-waits: a full channel parks the sender, an empty one parks the
+Neither side busy-waits: a full queue parks the sender, an empty one parks the
 receiver, and each operation wakes the other side when it makes progress possible.
 
 Two details make it correct:
@@ -45,47 +81,53 @@ Two details make it correct:
   CPU. `waitLocked` / `wakeLocked` are the variants that assume the caller already
   holds that critical section.
 
-## Verifying it
+### Verifying it
 
 The `ipc` test (see [testing.md](../testing.md)) runs a producer and a consumer passing
-**100 messages through a 4-slot channel**. The small buffer means the channel goes
+**100 messages through a 4-slot queue**. The small buffer means the queue goes
 full and empty over and over, so both the blocking-send and blocking-receive paths are
 exercised heavily. The messages arrive intact and in order (their sum is the
 expected `5050`), and neither task busy-waits — they block and wake each other.
 
-## Endpoints: call/reply across address spaces
+## Endpoints: the termination points
 
-A channel connects two kernel threads sharing one address space. Real servers are
+A queue connects two kernel threads sharing one address space. Real providers are
-*processes*, so the payload has to cross an address-space boundary. That's
+*processes*, so a packet has to cross an address-space boundary. That's
 `system/kernel/ipc-synchronous.zig`, and its shape is L4's: a synchronous **rendezvous** at an
-`Endpoint`, with the message copied directly from the sender's pages to the receiver's
+`Endpoint`, with the packet copied directly from the sender's pages to the receiver's
 (`copyAcross` walks both sets of page tables through the physmap — no CR3 switch, no
 bounce buffer).
 
-Two syscalls carry it:
+Two syscalls carry the request/reply exchange:
 
-- **`ipc_call(h, msg, reply)`** — copy `msg` to the server, block until it replies.
+- **`ipc_call(h, msg, reply)`** — copy the request packet to the provider, block
+  until the reply packet comes back.
 - **`ipc_reply_wait(h, reply, recv)`** — reply to the client you're still holding (if
-  any), then block for the next request. One syscall, because a server's steady state
+  any), then block for the next request. One syscall, because a provider's steady state
   is *always* "finish the last one, wait for the next".
 
 An endpoint is reached by **handle** — a small integer index into the process's handle
-table (`Task.handles`), exactly like a file descriptor, and just as unforgeable. The
+table (`Task.handles`), exactly like a file descriptor, and just as unforgeable.
-bootstrap problem (how do you get the first handle?) is solved by a tiny name registry:
+The provider never learns the client's identity beyond the **badge** delivered
-a server calls `ipc_register(service_id, h)` under a well-known small integer, and a
+alongside each packet: the caller's task id, stamped by the kernel —
-client calls `ipc_lookup(service_id)`.
+unforgeable source addressing, a property a network's source field lacks.
 
-The server never learns the client's identity beyond a **badge**, delivered alongside
+The bootstrap problem — how a channel is first established — is the subject of
-the message: the caller's task id.
+[protocol-namespace.md](../os-development/protocol-namespace.md): a protocol is
+resolved by name and the channel arrives as a capability. (The mechanism it
+replaced — `ipc_register`/`ipc_lookup` under compile-time `ServiceId` integers —
+is gone: both syscalls and the enum were deleted when the registry landed, and
+their syscall numbers are left vacant.)
 
-### Interrupts are messages too
+### Interrupts are signals
 
-`notifyFromIsr` posts an *asynchronous* notification to an endpoint — no payload, no
+`notifyFromIsr` posts an *asynchronous* signal to an endpoint — no payload, no
 reply owed — and wakes whoever is blocked in `reply_wait`. Its badge has the top bit
 set (`notify_badge_bit`), which is how a driver's single event loop distinguishes "a
-client wants something" from "the hardware wants something". Notifications sit in a
+client wants something" from "the hardware wants something". Signals sit in a
 small coalescing ring on the endpoint, so an interrupt taken while the driver was busy
-elsewhere is not lost.
+elsewhere is not lost — coalesced, never dropped, which is exactly a signal's
+contract (the *count* may collapse; the *fact* may not).
 
 This is what makes a user-space driver possible at all, and it's the subject of
 [drivers.md](drivers.md).
@@ -93,40 +135,65 @@ This is what makes a user-space driver possible at all, and it's the subject of
 ## What's next (partly done since)
 
 - **Priority inheritance** through IPC — still open: a high-priority client
-  blocked on a low-priority server suffers unbounded priority inversion.
+  blocked on a low-priority provider suffers unbounded priority inversion.
 - **Handle transfer.** *Landed as cap-passing (M13)*: `ipc_call` and
   `ipc_reply_wait` carry an optional capability alongside the bytes (`send_cap`),
-  copying an endpoint or shared-memory handle into the peer's table. First user:
+  copying an endpoint or shared-memory handle into the peer's table — the
-  [input](input.md) subscribers register by handing over their own endpoint, and
+  mechanism by which channels are established and private channels built. First
-  class drivers get a private channel to one device.
+  user: [input](input.md) subscribers register by handing over their own
+  endpoint, and class drivers get a private channel to one device.
 - **Asynchronous / buffered send** for the cases where a rendezvous is the wrong
-  shape (logging, notifications between servers). *Landed as `ipc_send`* — a
+  shape (logging, event fan-out). *Landed as `ipc_send`* — a
-  non-blocking post to an endpoint's bounded payload queue, delivered through
+  non-blocking post of an event packet (≤ 64 bytes) to an endpoint's bounded
-  `reply_wait` as a buffered message (badge bit `notify_message_bit`). Built for, and
+  queue, delivered through `reply_wait` (badge bit `notify_message_bit`). Built
-  first used by, the [input service](input.md)'s keyboard-event broadcast, where a
+  for, and first used by, the [input service](input.md)'s keyboard-event
-  synchronous push would let one dead subscriber hang the fan-out. A full queue drops
+  broadcast, where a synchronous push would let one dead subscriber hang the
-  the oldest (discrete messages, not a coalescing level like the notification ring).
+  fan-out. A full queue drops the oldest — event packets are droppable by
-- **A bounded reply** — half landed. The copy is still 256 bytes
+  design ([protocol-namespace.md](../os-development/protocol-namespace.md)'s
-  (`MESSAGE_MAXIMUM`) under the big kernel lock, but bulk transfer got its shared
+  wiring section states the rule).
+- **A bounded reply** — half landed. The copy is still one packet
+  (256 bytes) under the big kernel lock, but bulk transfer got its shared
   pages: `shared_memory_create`/`map`/`physical`, the region handle delegated as
-  a capability (above). virtio-gpu's scanout surface is the first user
+  a capability (above) — the packets-never-fragment rule in practice.
+  virtio-gpu's scanout surface is the first user
   ([display-v2.md](display-v2.md)).
 
 ## Lifecycle conventions over IPC (M17)
 
 Three conventions from [process-lifecycle.md](../os-development/process-lifecycle.md) ride the
-notification mechanism:
+signal mechanism:
 
-- **Signals** arrive as notifications on the endpoint a process nominated with
+- **Process signals** arrive as endpoint signals on the endpoint a process
-  `signal_bind` (`process.bindSignals`): badge = the signal bit plus the
+  nominated with `signal_bind` (`process.bindSignals`): badge = the signal bit
-  coalesced pending mask (`process.signalsFrom` decodes). Statements,
+  plus the coalesced pending mask (`process.signalsFrom` decodes). Statements,
   never questions; no payload, no reply.
 - **One-shot timers** (`timer_bind`, `time.timerOnce`) land as a
-  timer-bit notification — the timed wait: a service arms a deadline and keeps
+  timer-bit signal — the timed wait: a service arms a deadline and keeps
   serving, instead of blocking in sleep.
+- **Kernel notifications go only to your own endpoint.** `signal_bind`,
+  `timer_bind`, `process_subscribe`, `irq_bind`, `msi_bind`, and spawn's exit
+  endpoint all *nominate where the kernel will speak*, and all of them refuse an
+  endpoint the caller did not create (`-EPERM`; the check is `ipc.ownedBy`,
+  normalized to the process, so any thread may nominate an endpoint a sibling
+  created). Holding a handle is not enough, because holding a handle is cheap:
+  `fs_resolve` installs a mounted backend's capability in *any* caller's table,
+  so every process holds a handle to PID 1's mailbox. Without the rule, "bind
+  init's endpoint, then signal yourself" is a genuine, kernel-stamped `terminate`
+  badge in PID 1's queue — a shutdown a receiver has no way to disbelieve — and
+  timers, which carry no identity at all, multiply any loop that re-arms on its
+  own landing.
+- **A capability that arrives belongs to the turn.** The kernel installs a sent
+  capability in the receiver's table whatever the message's length or kind, so a
+  receive loop must dispose of one on *every* path — the ping, the notification,
+  the malformed request. The service harness (`service.run`) and PID 1 both hold
+  it in an `ipc.Arrival`, released by a `defer`, and a handler that means to keep
+  it says `take()`: forgetting closes, keeping is explicit. The reverse
+  arrangement leaks a handle-table slot per request, and thirty-two unauthorized
+  zero-length pings then end a service's ability to accept any capability —
+  no subscribe, no shared-memory handover — for the rest of the boot.
 - **The universal ping**: a **zero-length request is the liveness probe**,
   answered with a zero-length reply by the service harness itself
   (`service.run`). No protocol's requests start at length zero, so the
   encoding cannot collide, and a wedged service simply fails to answer — which
   is the diagnosis. Deep health ("can I reach my hardware?") stays a per-service
-  protocol message.
+  protocol packet.

docs/device-driver-development/new-driver-checklist.md

@@ -0,0 +1,218 @@
+# New driver: the minimum steps
+
+The shortest path from "a device shows up in the boot log" to "my process is
+running with its registers mapped". This is the checklist; the reasoning behind
+every step lives in [Writing a driver](drivers.md), the matching rules in
+[devices.csv](devices-csv.md), and interrupts in
+[device interrupts](device-interrupts.md).
+
+Worked example throughout: the Intel UHD 750 iGPU, which the boot log reports as
+
+```
+pci-bus: 0:2.0  bus=pci base=03 class=00 prog_if=00 vendor=8086 device=4C8A ...
+```
+
+## 1. Create the source file
+
+`system/drivers/<name>/<name>.zig` — kebab-case, abbreviations spelled out
+([coding standards](../coding-standards.md)). The directory name, the binary
+name, and the `devices.csv` driver path must all agree; a mismatch fails
+silently (the device-manager logs the spawn failure, nothing else happens).
+
+The complete minimal driver — claims its device, logs every resource, maps the
+register window, then sleeps in the harness loop:
+
+```zig
+//! /system/drivers/intel-uhd-graphics-750 — spawned by the device manager with
+//! the device-tree id as argv[1]; claims that device and no other.
+
+const std = @import("std");
+const device = @import("driver");
+const ipc = @import("ipc");
+const memory = @import("memory");
+const process = @import("process");
+const service = @import("service");
+
+/// No protocol yet: the kernel's IPC ceiling (MESSAGE_MAXIMUM) sizes the buffers.
+const message_maximum = 256;
+
+var controller_id: u64 = 0;
+var register_base: usize = 0;
+
+fn initialise(endpoint: ipc.Handle) bool {
+    _ = endpoint; // needed later, for irq binding and timers
+
+    if (!device.claim(controller_id)) {
+        std.log.err("unable to claim device {d}", .{controller_id});
+        return false;
+    }
+
+    // Fetch our own descriptor back for the device's resources.
+    const buffer = memory.allocator().alloc(device.DeviceDescriptor, 64) catch return false;
+    defer memory.allocator().free(buffer);
+    const total = device.enumerate(buffer);
+    const descriptor = for (buffer[0..@min(total, buffer.len)]) |d| {
+        if (d.id == controller_id) break d;
+    } else {
+        std.log.err("device {d} not in the device tree", .{controller_id});
+        return false;
+    };
+
+    // Log every resource BEFORE choosing one (see step 5).
+    var register_index: u64 = 0;
+    for (descriptor.resources[0..@intCast(descriptor.resource_count)], 0..) |resource, index| {
+        std.log.info("resource {d}: kind={d} start=0x{x} len=0x{x}", .{
+            index, resource.kind, resource.start, resource.len,
+        });
+        // The 16 MiB window is GTTMMADR, the register BAR (this device also has
+        // a 256 MiB memory BAR, GMADR — "first memory resource" would be wrong).
+        if (resource.kind == @intFromEnum(device.ResourceKind.memory) and
+            resource.len == 16 * 1024 * 1024) register_index = index;
+    }
+    if (register_index == 0) {
+        std.log.err("register BAR not found", .{});
+        return false;
+    }
+
+    register_base = device.mmioMap(controller_id, register_index) orelse {
+        std.log.err("mmio_map failed", .{});
+        return false;
+    };
+    std.log.info("registers mapped at 0x{x}", .{register_base});
+    return true;
+}
+
+fn onMessage(message: []const u8, reply: []u8, sender: u32, capability: ?ipc.Handle) usize {
+    _ = message;
+    _ = reply;
+    _ = sender;
+    _ = capability;
+    return 0; // no protocol yet; the zero-length ping is answered by the harness
+}
+
+pub fn main(init: process.Init) void {
+    const argument = init.arguments.get(1) orelse {
+        std.log.err("missing device id (argv[1])", .{});
+        return;
+    };
+    controller_id = std.fmt.parseInt(u64, argument, 10) catch {
+        std.log.err("malformed device id '{s}'", .{argument});
+        return;
+    };
+    service.run(message_maximum, .{
+        .init = initialise,
+        .on_message = onMessage,
+        // .on_notification only once an IRQ or timer is bound
+    });
+}
+```
+
+`claim` is the capability gate: MMIO mapping, DMA grants, and IRQ binding all
+require it, and it pins the IOMMU domain to this process
+([drivers.md — claim before touch](drivers.md#the-capability-claim-before-touch)).
+
+## 2. Create the build package and register it in the root build
+
+The driver directory is its own build package
+([build-packages-plan.md](../build-packages-plan.md)): a ~15-line `build.zig`
+plus a `build.zig.zon` beside the source. Copy both from an existing driver —
+`system/drivers/pci-bus/` is the template — and adjust the name, root source
+file, and the import list. The list names EXACTLY the modules the driver's
+source `@import`s (the moral equivalent of its include list; an undeclared
+import is a compile error):
+
+```zig
+pub fn build(b: *std.Build) void {
+    const exe = build_support.userBinary(b, .{
+        .name = "intel-uhd-graphics-750",
+        .root_source_file = b.path("intel-uhd-graphics-750.zig"),
+        .imports = &.{ "driver", "ipc", "memory", "process", "service" },
+    });
+    b.installArtifact(exe);
+}
+```
+
+The zon declares `build-support`, `kernel` (implicit in every binary: the root
+shim lives there), and the homes of the listed imports — for the minimal
+driver above that is kernel alone plus `device` (for `driver`); add
+`protocol`, `client`, ... only when an import comes from them (again, copy
+pci-bus's zon and adjust). For the `.fingerprint` field, leave the copied
+value in place and `zig build` will reject it and suggest the fresh one to
+paste.
+
+Then three one-liners in the root build register the package: the dependency
+and a row in the boot-tree array in `build.zig` (search for
+`virtio_gpu_package` to land in the right places),
+
+```zig
+const intel_uhd_graphics_750_exe = b.dependency("intel-uhd-graphics-750", .{}).artifact("intel-uhd-graphics-750");
+```
+
+```zig
+.{ .path = "system/drivers/intel-uhd-graphics-750", .binary = intel_uhd_graphics_750_exe.getEmittedBin() },
+```
+
+and the path entry in the root `build.zig.zon`:
+
+```zig
+.@"intel-uhd-graphics-750" = .{ .path = "system/drivers/intel-uhd-graphics-750" },
+```
+
+Without the boot-tree row the binary never reaches the image and the
+device-manager has nothing to spawn. (The package also builds standalone:
+`cd system/drivers/intel-uhd-graphics-750 && zig build`.)
+
+## 3. Add the match rule to `etc/devices.csv`
+
+One row: bus, class triplet, vendor/device, driver path. **Copy the class
+triplet from the pci-bus boot log line, not from another row** — for the iGPU
+above the correct rule is
+
+```
+pci,    03,  00,   00,     8086,  4C8A,  *,        *,        /system/drivers/intel-uhd-graphics-750
+```
+
+Field-by-field rules and the most-specific-wins policy: [devices.csv](devices-csv.md).
+The registry is authoritative: an unmatched device is logged unbound, never
+guessed — so a wrong nibble here means the driver simply never starts.
+
+## 4. First contact: read, predict, verify
+
+Before writing any register, read one whose value you can predict from state
+the firmware already programmed (for a display controller: the pipe source
+size of the live mode). Registers are volatile loads at `register_base +
+offset`, where `offset` is what the device's manual lists:
+
+```zig
+fn read32(offset: usize) u32 {
+    return @as(*volatile u32, @ptrFromInt(register_base + offset)).*;
+}
+```
+
+A matching read proves the whole chain — CSV match, spawn, claim, BAR choice,
+mapping — with zero risk to the hardware.
+
+## 5. Verify the plumbing
+
+- `zig build test` still passes.
+- On the image: `/var/log/<boot-stamp>/system/services/device-manager.log`
+  shows `spawned <name> for device <N>`, and
+  `/var/log/<boot-stamp>/system/drivers/<name>.log` holds the resource list and
+  your first read.
+- If the driver did not spawn, diagnose in this order: binary on the image
+  (step 2) → CSV row matches the log line exactly (step 3) → path identical in
+  both (step 1).
+
+## Later, when the device needs them
+
+- **Interrupts**: MSI/MSI-X via the `pci` module, delivered as notifications to
+  `on_notification` — see [device interrupts](device-interrupts.md) and the
+  xHCI driver's `setupMsi` (QEMU trap documented there: enable MSI-X before
+  unmasking the device's own interrupt-enable bit).
+- **DMA**: grant-backed buffers, bounded by the IOMMU domain established at
+  claim time ([driver model](driver-model.md)).
+- **Children**: a bus driver publishes what it finds via `device_register`
+  ([drivers.md — publishing children](drivers.md#publishing-children-device_register)).
+- **A protocol**: replace `message_maximum` with the protocol's own maximum and
+  dispatch on the operation word in `onMessage` — every service under
+  `system/services/` is an example.

docs/dynamic-libraries.md

@@ -0,0 +1,124 @@
+# Dynamic libraries on danos
+
+A design note and milestone plan for shared objects: building them, loading them
+with `dlopen`, and — the part that needs kernel work — actually *sharing* them
+between processes. Directional, post-P5 of
+[python-on-danos-milestones.md](python-on-danos-milestones.md); nothing on the
+CPython bring-up path depends on it.
+
+## Reconciling the earlier "rejected"
+
+Dynamic libraries were evaluated once before and rejected — but as an answer to a
+*different question*: whether they could claw back ReleaseSafe's measured ~2×
+code size. They cannot (the safety checks inline at every call site; no library
+scheme dedups them), and that verdict stands for that question. The reasons to
+build them now are the ones that investigation never weighed:
+
+- **`ctypes` and runtime FFI** — Python calling into a danos library without
+  rebuilding the interpreter. This is the piece that makes Python prototyping
+  self-serve: drop a `.so` on the image, `ctypes.CDLL` it, iterate.
+- **Loadable CPython extension modules** — today every C extension means
+  relinking the interpreter (`Modules/Setup`); with `dlopen`, an extension is a
+  file.
+- **One interpreter image, many Python services** — a statically-linked CPython
+  is tens of megabytes *per process*. A shared `libpython` mapped read-only once
+  (milestone D3 below) makes Python services cheap enough to be the default way
+  to prototype one.
+- **Plugin-shaped applications** — the UI toolkit and the terminal will want
+  them eventually.
+
+The scoping that dissolves the apparent contradiction is the **size doctrine**:
+leanness is an *operating-system* property — the kernel and system services stay
+small and statically linked, and none of them ever link the loader — while
+*applications* have their own budget and may be big. Dynamic libraries are an
+**application-layer facility**, full stop.
+
+What also does **not** change: the public ABI stays the vDSO + the IPC
+protocols. Shared objects are artifacts *within* one system image, versioned by
+the build — not a new stable ABI surface for the OS.
+
+## Design
+
+- **Format and codegen are free.** ELF shared objects with position-independent
+  code; `zig cc -fPIC -shared` against the [libdanos-c](c-library-compatibility.md)
+  sysroot already emits them. The work is entirely on the loading side.
+- **The loader lives in userspace, inside the libc.** `dlopen` reads the `.so`
+  through the VFS, maps its segments, applies relocations, resolves symbols
+  against the process and the `DT_NEEDED` dependency graph, runs constructors,
+  returns a handle. No kernel loader changes in v1 — segments land in anonymous
+  `mmap` as private copies.
+- **Bind-now, always.** All relocations resolved at `dlopen` time
+  (`RTLD_NOW` semantics only). Lazy PLT binding buys startup latency danos does
+  not care about, at the price of a writable GOT dance and a much subtler
+  loader. Not worth it; keep it out permanently.
+- **W^X from day one.** Map, relocate, then flip text pages read-execute —
+  which requires memory-protection change (`mprotect`-shaped) in the danos
+  `mmap` surface if it is not already there. No page is ever writable and
+  executable at once.
+- **TLS in shared objects is deferred.** Thread-local storage models
+  (initial-exec vs. general-dynamic) are the deep end of every dynamic linker.
+  v1 refuses a `.so` with a TLS segment; revisit alongside the post-P5 pthread
+  subset, which is when it could matter.
+- **Executables stay static until D4.** v1 is "a static binary that can
+  `dlopen`" — no `PT_INTERP`, no program interpreter, no dynamically-linked
+  `main` binaries. That keeps process startup untouched.
+
+## Milestones
+
+1. **D1 — dlopen in-process.** The `.so` build target; the loader in libdanos-c:
+   map, relocate (`RELATIVE`/`GLOB_DAT`/`JUMP_SLOT`), resolve, constructors;
+   `dlopen`/`dlsym`/`dlerror`/`dlclose`; private anonymous mappings; no TLS.
+   *Test:* QEMU `dlopen-hello` — load a `.so`, call a symbol, unload, reload.
+2. **D2 — the FFI payoff.** `DT_NEEDED` dependency graphs; a **libffi port**
+   (x86-64 SysV assembly is upstream; the port is its closure-allocation paths,
+   which must respect W^X); CPython's `ctypes` enabled; extension modules
+   loadable from file. *Test:* QEMU — a Python script `ctypes.CDLL`s a danos
+   `.so` and round-trips a call; a `.so` extension module imports.
+3. **D3 — actual sharing (the kernel milestone).** Shared read-only file-backed
+   mappings — a page-cache-shaped facility so N processes mapping `libpython`
+   hold one physical copy. This is the memory-win milestone and the only one
+   touching the kernel; design it with the existing shm machinery in view
+   (the shared-fate walks already locked the relevant paths). *Test:* N Python
+   services up; measure physical pages against N× the static baseline.
+4. **D4 — dynamically-linked executables** (optional, evaluate after D3):
+   `PT_INTERP`, a danos program interpreter, and the spawn path teaching the
+   loader about it. Only worth it if the image-size or update story demands it.
+
+## Risks and gotchas
+
+- **Scope creep is the failure mode.** Every dynamic linker grows toward glibc.
+  The fences: bind-now only, no lazy binding ever, no TLS until pthreads demand
+  it, no dlopen-from-memory, no versioned symbols. Each fence removed is a
+  design discussion, not a patch.
+- **Code loading is a security event.** `dlopen` turns file bytes into executable
+  code, so W^X discipline is table stakes and *what may be dlopened* is a
+  capability question — the natural danos answer is that loadability follows VFS
+  readability of the `.so`, and services' images are supervised like any other
+  artifact. Revisit explicitly at D3 when mappings become shared.
+- **`dlclose` is where loaders go to die.** Constructors/destructors,
+  dangling function pointers, re-open identity. Keep v1 semantics honest and
+  simple: `dlclose` runs destructors and unmaps; holding pointers past it is
+  undefined; no reference-counted deferral cleverness.
+- **The ReleaseSafe fact still applies to `.so`s** — a ReleaseSafe shared object
+  carries its inlined checks like any static code; D3's sharing saves *copies*,
+  not check overhead. Size expectations should be set accordingly.
+
+## Decisions needing sign-off
+
+- Dynamic libraries join the roadmap at all (this note exists because the
+  earlier size-motivated rejection was re-opened for ABI/sharing reasons).
+- **Bind-now only; no lazy binding, permanently.**
+- **Loader in userspace libc; kernel involvement only at D3** (shared read-only
+  mappings).
+- **Static executables until D4**, and D4 only on demonstrated need.
+
+## Related
+
+- [c-library-compatibility.md](c-library-compatibility.md) — the sysroot the
+  loader ships in; its absence table gains `dlfcn.h` at D1.
+- [python-on-danos.md](python-on-danos.md) — the `ctypes` story this unlocks.
+- [python-on-danos-milestones.md](python-on-danos-milestones.md) — sequencing;
+  this work is post-P5.
+- [os-development/memory-map.md](os-development/memory-map.md) /
+  [os-development/paging.md](os-development/paging.md) — where W^X and shared
+  mappings land.

docs/file-system-development/danos-file-system-hierarchy-FSH.md

@@ -1,128 +0,0 @@
-# DanOS Filesystem Hierarchy Standard (DFHS)
-
-Most modern Unix and Unix-like operating systems follow the FHS. DanOS has its own FHS structure which extends the unix FHS. Root path resolution is provided by the kernel-resident VFS root (`fs_resolve`, `system/kernel/vfs.zig`); mounted filesystem servers serve the subtrees they own.
-
-## Directory structure
-
-| Path             | Description                                                                                                                                                         |
-|------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------|
-| /                | Primary hierarchy root and root directory of the entire file system hierarchy.                                                                                      |
-| /bin             | Essential command binaries that need to be available in single-user mode, including to bring up the system or repair it, for all users (e.g., cat, ls, cp).         |
-| /boot            | Boot loader files (e.g., EFI, initial-ramdisk.img ).                                                                                                                |
-| /dev             | POSIX Device files (e.g., /dev/null, /dev/disk0, /dev/tty, /dev/random).                                                                                            |
-| /etc             | Host-specific system-wide configuration files.                                                                                                                      |
-| /home            | Users' home directories, containing saved files, personal settings, etc.                                                                                            |
-| /lib             | Libraries essential for the binaries in /bin and /sbin. eg realtime, system, ipc etc.                                                                               |
-| /sbin            | Essential system binaries (e.g init)                                                                                                                                |
-| /srv             | Site-specific data served by this system, such as data and scripts for web servers, data offered by FTP servers, and repositories for version control systems       |
-| /system          | DanOS operating system files (similar idea to C:\Windows). A true representation of danos — its layout mirrors the source tree, so `/system` is what danos *is*.    |
-| /system/devices  | danos virtual device tree e.g. similar to /sys on linux but with danos device tree conventions (the structures in the devices module)                               |
-| /system/drivers  | driver binaries, one sub-project each (e.g. /system/drivers/pci-bus, /system/drivers/ps2-bus)                                                                       |
-| /system/services | system-service binaries — init, the FAT server, and other user-mode servers (e.g. /system/services/init, /system/services/fat)                                      |
-| /system/kernel   | the kernel image                                                                                                                                                    |
-| /test            | Test fixtures for the QEMU integration suite. Read-only and initrd-backed like /system, and its layout likewise mirrors the source tree (the repo's test/ directory). Present on development and test images; a volume without it still boots. |
-| /test/system/services | test-fixture binaries (e.g. /test/system/services/vfs-test, /test/system/services/thread-test) — the same path in the repo source tree and on the boot volume  |
-| /tmp             | Directory for temporary files (see also /var/tmp). Often not preserved between system reboots and may be severely size-restricted.                                  |
-| /usr             | Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications. Should be shareable and read-only.                   |
-| /var             | Variable files: files whose content is expected to continually change during normal operation of the system, such as logs, spool files, and temporary e-mail files. |
-
-## File types
-
-POSIX specifies the long format of the ls command to represent the Unix file type as the first letter for an entry.
-
-| type              | symbol | Description                                                                                                                                                           |
-|-------------------|--------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
-| regular           | -      | An ordinary file holding an uninterpreted byte stream. Reads and writes are positional, and the file grows on demand (e.g., a binary in /bin, a config file in /etc). |
-| directory         | d      | A container mapping names to other files. It may only be modified through directory operations, never written to directly.                                            |
-| symbolic link     | l      | A file whose contents are a path that is resolved in its place. The target need not exist, and may cross mount points.                                                |
-| FIFO special      | p      | A named pipe: an in-order byte stream between processes, where writers block until a reader opens the other end.                                                      |
-| block special     | b      | A device node addressed in fixed-size blocks with the kernel free to buffer and reorder access (e.g., /dev/disk0).                                                    |
-| character special | c      | A device node addressed as an unbuffered byte stream, delivered to the driver in order (e.g., /dev/tty, /dev/null).                                                   |
-| socket            | s      | A named endpoint for bidirectional message-passing between processes, bound to a path rather than an address.                                                         |
-
-## /dev
-
-`/dev` holds the names through which processes reach devices. It is deliberately not
-the device tree: the tree — every node discovered by ACPI or PCI enumeration, with its
-resources and its parent — lives under [/system/devices](#directory-structure) and is
-addressed by device id. `/dev` is the much smaller set of devices that have a driver
-willing to serve them, addressed by name.
-
-A device node is not a file the VFS can read. The bytes live in a driver process
-([drivers.md](../device-driver-development/drivers.md)), so opening a `/dev` name has to resolve to that driver's
-IPC endpoint, and subsequent reads and writes are calls against it. Resolve-to-endpoint
-is exactly what the kernel's `fs_resolve` already does for any mounted backend, and
-`FileStatus.kind` is the field that marks a device node; **what is not implemented today
-is `/dev` itself** — no service mounts it. (The flat eight-node ramfs this section once
-described is retired: the kernel-resident VFS root in `system/kernel/vfs.zig` serves a
-read-only initrd mount per top-level tree — `/system`, and `/test` on images that carry
-the fixtures — with real directories and node kinds, and filesystem
-backends such as the FAT server mount the rest.) The three sections below describe the
-intended shape, and are honest about which parts the kernel can already support.
-
-### Character devices
-
-A character device is a byte stream with no addressable position: bytes are delivered
-to the driver in the order written, and a read consumes what is there. Terminals,
-serial lines, keyboards and mice are all of this shape. These are the natural first
-device nodes in danos, because a character driver needs nothing the kernel doesn't
-already provide — it claims its device, maps its registers with `mmio_map`, and blocks
-on `replyWait` for either an interrupt or a client request. `system/drivers/ps2-bus/ps2-bus.zig`
-is already that program, minus the file-node client half.
-
-The obstacle was never the file type; it is which hardware a ring-3 driver can reach.
-Direct `in`/`out` from user space is still a #GP (no TSS I/O bitmap, IOPL never raised),
-but a driver no longer needs it: **`io_read`/`io_write`** grant port access the same way
-`mmio_map` grants memory — gated by `device_claim` and the device's discovered `io_port`
-resource. So the 16550 UART at `0x3F8` and the PS/2 controller at `0x60`/`0x64` (and thus
-`/dev/ttyS0` and a keyboard node) are now writable as ordinary ring-3 drivers; the
-low-rate legacy hardware that needs port I/O is fine with a syscall per access. A
-memory-mapped device such as the framebuffer, needing no port I/O at all, remains the
-easiest first entry.
-
-### Block devices
-
-A block device is addressed in fixed-size blocks and, unlike a character device, the
-layer above is free to buffer, reorder, coalesce and retry requests against it. Disks
-and other persistent storage are the whole population of this class.
-
-A block driver is now **writable, but not yet memory-safe.** Every storage controller
-worth naming is a bus master: it is programmed by handing it the physical address of a
-descriptor ring and left to read and write memory on its own. That ring is exactly what
-**`dma_alloc`** now provides — physically contiguous, pinned, uncacheable, with its
-physical address disclosed — and **`/lib/device/mmio`**'s barriers order the descriptor writes
-against the doorbell, and **`msi_bind`** delivers completions. So an AHCI or NVMe driver
-can be written today (the M14/M15 work in [driver-model.md](../device-driver-development/driver-model.md); the earlier
-"cannot host a block driver at all" is no longer true).
-
-What is *not* yet true is that it is safe. A device programmed with an arbitrary physical
-address writes to arbitrary physical memory, and page tables do not sit between a device
-and RAM — an IOMMU does. The IOMMU is now *detected* (M16), but no translation domains
-are programmed, so granting a DMA-capable device to a driver process is still equivalent
-to granting ring 0. Until per-device domains confine a driver's DMA to the buffers it
-`dma_alloc`'d, a block driver works but forfeits the isolation that motivates user-space
-drivers — enforcement is the next step, and lands with that first driver. A ramdisk over
-the initial ramdisk remains the one block-shaped thing that needs no driver process at all.
-
-### Pseudo-devices
-
-A pseudo-device has the interface of a device and no hardware behind it: `/dev/null`
-discarding writes and reading as end-of-file, `/dev/zero` reading as an endless run of
-zero bytes, `/dev/full` failing writes with `ENOSPC`, `/dev/random` and `/dev/urandom`
-yielding unpredictable bytes.
-
-These are the only `/dev` entries danos can implement immediately, and they are the
-sensible place to start, because they are exactly the entries that need no driver
-process, no `device_claim`, no MMIO grant and no interrupt. A future pseudo-device
-service would answer them out of its own address space — `null` and `zero` are a few
-lines each in its `read` and `write` handlers — and mount itself at `/dev` the way the
-FAT server mounts `/mnt/usb`. The two pieces of structure every later device node
-depends on (and that the flat ramfs of the time lacked) exist now: directories, so that
-`/dev/null` is a path rather than a name; and a populated `FileStatus.kind`, so that a
-caller can tell a character device from a regular file.
-
-`/dev/random` is the one that is not free. It needs an entropy source, and the honest
-options on this kernel are `RDRAND`/`RDSEED` where CPUID advertises them, and the HPET
-counter's low bits as a poor fallback. Neither is a seeded CSPRNG, and a `/dev/random`
-that is merely unpredictable-looking is worse than none — nothing should be keyed from
-it until it is a real one.

docs/file-system-development/file-system-hierarchy.md

@@ -0,0 +1,90 @@
+# The danos file-system hierarchy
+
+danos is not unix, and its tree does not follow the unix FHS. Paths are the
+system's universal namespace — files, the device inventory, and protocol
+endpoints all live in one tree — but what a path *yields* differs by subtree:
+bytes, facts, or a connection. Root path resolution is provided by the
+kernel-resident VFS root (`fs_resolve`, `system/kernel/vfs.zig`); mounted
+backends serve the subtrees they own.
+
+Naming follows the codebase conventions: kebab-case, full words, no
+abbreviations. Every top-level name says what its subtree *is*.
+
+## The tree
+
+| Path                    | What it is                                                                                                                                              |
+|-------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `/`                     | The root of the one namespace.                                                                                                                          |
+| `/applications`         | Installed applications, one directory per application — the directory is the identity, the same rule as source sub-projects. *(Planned; empty today.)*  |
+| `/protocol`             | The contract namespace: one protocol node per contract, grouped into directories by domain (`/protocol/display`, `/protocol/networking/ip`). Synthetic — no bytes; opening a name yields a connection to the current provider. See [protocol-namespace.md](../os-development/protocol-namespace.md). |
+| `/system`               | The operating system — what danos *is*. Its program subtrees mirror the source tree exactly.                                                            |
+| `/system/kernel`        | The kernel image.                                                                                                                                       |
+| `/system/drivers`       | Driver binaries, one per sub-project (`/system/drivers/pci-bus`, `/system/drivers/ps2-bus`).                                                            |
+| `/system/services`      | System-service binaries (`/system/services/init`, `/system/services/fat`).                                                                              |
+| `/system/devices`       | The device inventory: every node hardware discovery found, with its resources and parent — the structures of the devices module, as a browsable virtual tree. Informational only; you *read about* hardware here and *talk to* it through `/protocol`. *(Planned; served by device-manager.)* |
+| `/system/configuration` | Machine configuration (`init.csv`, `devices.csv`). Writable, served from the boot volume.                                                               |
+| `/system/logs`          | Per-boot logs: `/system/logs/<boot-stamp>/<binary-path>.log`. Writable, served from the boot volume.                                                    |
+| `/test`                 | Test fixtures for the QEMU integration suite. Read-only and initrd-backed like the program subtrees of `/system`, mirroring the repo's `test/` directory. Present on development and test images; a volume without it still boots. |
+| `/volumes`              | Attached storage volumes, one directory per volume (`/volumes/usb`). A volume's own tree appears beneath its name.                                      |
+
+Read-only and writable halves of `/system`: the program subtrees (`kernel`,
+`drivers`, `services`) and the future `devices` are immutable at runtime —
+initrd-backed or synthetic — while `configuration` and `logs` are mutable
+machine state served by the boot-volume FAT backend. The kernel's
+reserved-prefix rule (no mount may shadow `/system`, `/test`, or `/protocol`)
+needs a carve-out for exactly these two writable subtrees; that lands with the
+path migration below.
+
+Deliberately not defined yet: a temporary-files location and per-application
+mutable storage. Both belong to the `/applications` design and will be
+specified there, not guessed at here.
+
+## Node kinds
+
+What a path resolves to. These fill `FileStatus.kind` and
+`DirectoryEntry.kind` in the [vfs protocol](vfs-protocol.md)
+(`library/protocol/vfs/vfs-protocol.zig`); enum values are append-only.
+
+| Kind               | Meaning                                                                                                                                        |
+|--------------------|-------------------------------------------------------------------------------------------------------------------------------------------------|
+| `regular`          | An ordinary file: an uninterpreted byte stream, positional reads and writes, grows on demand.                                                   |
+| `directory`        | A container mapping names to nodes; modified only through directory operations.                                                                 |
+| `character_device` | A node whose read/write have **stream semantics**: unseekable, reads block until bytes exist, size is meaningless. The console and every tty-shaped node ([character-devices-and-tty.md](../character-devices-and-tty.md)); what a POSIX layer's `isatty` detects. |
+| `block_device`     | A node addressed in fixed-size sectors — a raw volume. Reserved: recognized, nothing serves one yet.                                            |
+| `symbolic_link`    | Reserved: a recognized value, not implemented by any backend.                                                                                   |
+| `fifo`             | Reserved for the future pipe object (wanted by the POSIX compatibility layer); not implemented.                                                 |
+| `protocol`         | A node naming a contract: `open` yields an IPC connection (an endpoint capability) instead of a file id — the kind of every leaf under `/protocol`. *(Being added; see protocol-namespace.md.)* |
+
+Note the layering: `protocol` says what *opening the name* does (you get a
+conversation); `character_device`/`block_device` say what *read and write
+mean* on a node a provider serves you. The two compose — `/protocol/console`
+is a protocol node in the registry, and the node opened over that connection
+reports `character_device`, which is what gives it stream semantics. Only
+`socket` is retired (its value stays reserved for wire stability): a named
+rendezvous point is exactly what a protocol node is.
+
+## What is deliberately absent
+
+There is no `/bin`, `/boot`, `/dev`, `/etc`, `/home`, `/lib`, `/mnt`, `/sbin`,
+`/srv`, `/tmp`, `/usr`, or `/var`. These encode unix history — the
+binary/library split of small disks, configuration-as-scattered-text, devices
+as magic files — that danos does not carry. A POSIX compatibility layer (the
+Python track's mini-libc) may *present* whichever of these its programs
+expect, mapped onto the real tree; the tree itself stays danos-native.
+
+## Migration
+
+The tree above is the specification; some code still writes the unix paths it
+replaced. The flag-day converting them:
+
+| Today (in code)                          | Becomes                                   | Where                                                          |
+|------------------------------------------|-------------------------------------------|-----------------------------------------------------------------|
+| `/etc/init.csv`                          | `/system/configuration/init.csv`          | `system/services/init/init.zig`                                |
+| `/etc/devices.csv`                       | `/system/configuration/devices.csv`       | `system/services/device-manager/device-manager.zig`            |
+| `/var/log/...`                           | `/system/logs/...`                        | `system/services/logger/logger.zig`, the FAT server's `/var` mount |
+| `/mnt/usb`                               | `/volumes/usb`                            | `system/services/fat/fat.zig`, the fat/vfs tests               |
+| `ServiceId` lookup                       | resolve + open under `/protocol`          | every service and client; [protocol-namespace.md](../os-development/protocol-namespace.md) |
+
+The boot-image builder and the on-volume directory layout move in the same
+change, so a freshly written image and the paths the services expect never
+disagree.

docs/file-system-development/vfs-protocol.md

@@ -6,7 +6,10 @@
 > serves it directly (the read-only /system initrd mount, via `fs_node`) or
 > redirects the caller to the owning backend's endpoint plus the rewritten
 > mount-relative path — after which the client speaks THIS protocol to the
-> backend, unchanged. The Zig source of truth is `library/protocol/vfs/vfs-protocol.zig`
+> backend, unchanged. Since P4a the contract is expressed through
+> `envelope.Define` (docs/os-development/protocol-namespace.md), so every
+> packet begins with the universal 16-byte prefix and the open-node id rides
+> in it. The Zig source of truth is `library/protocol/vfs/vfs-protocol.zig`
 > (the `vfs-protocol` module), whose unit test pins a sample of the sizes
 > and values below. This page is the **language-neutral wire specification**
 > of that contract — what a Rust or C client implements ([vdso.md](../os-development/vdso.md)
@@ -22,12 +25,17 @@ also hands back the path rewritten relative to the mount — not from a
 registry lookup. (Service id 1, the old userspace router, is retired.)
 
 - A message is at most **256 bytes** (`message_maximum`).
-- A request is a fixed 32-byte **Request** header followed by an inline
+- Every packet begins with the 16-byte **envelope prefix**
-  payload of at most **224 bytes** (`maximum_payload`) — a path, or write
+  ([protocol-namespace.md](../os-development/protocol-namespace.md)): a
-  bytes. There is no multi-message request: paths and single reads/writes
+  `Header` on a request, a `Status` on a reply. The prefix is **folded, not
-  must fit, and larger transfers loop (see *read* / *write*).
+  stacked** — the verb and the object being addressed live in it, and no
-- A reply is a fixed 24-byte **Reply** header followed by an inline payload —
+  request or reply below repeats either.
-  read bytes, a `FileStatus`, or a `DirectoryEntry`.
+- A request is the header, then the verb's own fixed part (0–16 bytes), then
+  an inline tail of at most **224 bytes** (`maximum_payload`) — a path, or
+  write bytes. There is no multi-message request: paths and single
+  reads/writes must fit, and larger transfers loop (see *read* / *write*).
+- A reply is the status, then the verb's own fixed part, then an inline tail
+  — read bytes, or a directory entry's name.
 - All integers are **little-endian**; layouts are C layout for x86-64
   (`extern struct`), offsets given below so nothing need be inferred.
 
@@ -37,91 +45,108 @@ With clients holding backend node ids directly, a backend records each open
 handle's owner and sweeps a dead client's handles via the published process
 exit events.
 
-## Request header — 32 bytes
+## Request header — 16 bytes
+
+The envelope's `Header`, identical in every danos protocol:
 
 | offset | size | field | meaning |
 |-------:|-----:|-------|---------|
-| 0 | 4 | `operation` | an **Operation** value (below) |
+| 0 | 4 | `operation` | an **Operation** value (below); 0–15 are the reserved universal verbs |
 | 4 | 4 | — | padding |
-| 8 | 8 | `node` | the server-side open-node id from a prior `open`; 0 for path-based operations |
+| 8 | 8 | `target` | **the open-node id** from a prior `open`; 0 for `open` itself and the path-based verbs |
-| 16 | 8 | `offset` | byte position for read/write; entry index (cursor) for readdir; else 0 |
-| 24 | 4 | `len` | payload length for path/write operations; requested byte count for read |
-| 28 | 4 | `flags` | open flags (below); else 0 |
 
-## Reply header — 24 bytes
+## Reply header — 16 bytes
+
+The envelope's `Status`:
 
 | offset | size | field | meaning |
 |-------:|-----:|-------|---------|
 | 0 | 4 | `status` | **0 = success**, negative = failure (signed) |
 | 4 | 4 | — | padding |
-| 8 | 8 | `node` | the new open-node id (for `open`); else 0 |
+| 8 | 4 | `len` | reply bytes following this header: the verb's fixed part plus its tail |
-| 16 | 4 | `len` | reply payload length in bytes |
+| 12 | 4 | — | padding |
-| 20 | 4 | — | padding |
 
-On failure the backend replies `status = -1`, and that reply reaches the
+A failing backend replies with the status alone (`len` = 0) and no fixed
-client directly — there is no party between them on the wire. (Kernel-served
+part, and that reply reaches the client directly — there is no party between
-paths produce no wire replies at all: `fs_resolve`/`fs_node` failures are
+them on the wire. (Kernel-served paths produce no wire replies at all:
-syscall register statuses.) A richer errno vocabulary is future work —
+`fs_resolve`/`fs_node` failures are syscall register statuses.) The errno
-clients must treat *any* negative status as failure, not match on -1.
+vocabulary is the kernel's, continued by the envelope: `ENOENT` = 4 is what a
+backend answers for anything it cannot find or cannot do, `ENOSYS` = 10 for a
+verb it does not implement, `EPROTO` = 11 for a packet shorter than the verb
+it names. Clients must treat *any* negative status as failure rather than
+matching a particular one.
 
 ## Operations
 
-Values are append-only and never renumbered (the same evolution rule every
+Values number from 16 (`first_protocol_operation`) in declaration order, and
-danos protocol follows). Send only values from this table: the shipped server
+are frozen once shipped. Values 0–15 are the envelope's reserved universal
-decodes the operation into an exhaustive enum, so an out-of-range value is
+verbs, which mean the same thing at every provider in the system: `describe`
-not answered with a `status = -1` reply — it trips a safety check in safe
+(0) answers the protocol's name and version and is implemented by the
-builds and is undefined otherwise. (The `-1` replies cover recognised but
+envelope itself, so every backend answers it. A verb outside this table is
-refused operations, such as `mount` sent to a backend.)
+answered `-ENOSYS`; it is never a safety check any more, because the
+dispatch compares numbers rather than decoding an enum.
 
-| value | operation | request payload | reply |
+Each row's *request* and *reply* name the bytes **after** the 16-byte prefix.
-|------:|-----------|-----------------|-------|
+
-| 0 | `open` | the path (`len` = its length), `flags` as below | `node` = open-node id |
+| value | operation | request | tail | reply | reply tail |
-| 1 | `close` | — (`node` set) | status only |
+|------:|-----------|---------|------|-------|-----------|
-| 2 | `read` | — (`node`, `offset`, `len` = wanted count) | `len` bytes read, payload = the bytes; `len` 0 at end of file |
+| 16 | `open` | `flags` (4 bytes, below) | the path | `node` (8 bytes) = the open-node id | — |
-| 3 | `write` | the bytes (`node`, `offset`, `len` = count) | `len` = bytes accepted (may be short — loop) |
+| 17 | `close` | — | — | — | — |
-| 4 | `status` | — (`node` set) | payload = **FileStatus** (24 bytes) |
+| 18 | `read` | `offset` (8), `len` (4) = wanted count | — | — | the bytes read; `Status.len` 0 at end of file |
-| 5 | `readdir` | — (`node` = a directory, `offset` = cursor) | payload = one **DirectoryEntry** + name; `len` 0 at end |
+| 19 | `write` | `offset` (8), `len` (4) = count | the bytes | `count` (4) = bytes accepted (may be short — loop) | — |
-| 6 | `mount` | the mount-point path; the backend endpoint rides as the call's **capability** | status only |
+| 20 | `status` | — | — | **FileStatus** (24 bytes) | — |
-| 7 | `unmount` | the mount-point path | status only |
+| 21 | `readdir` | `cursor` (8) | — | one **DirectoryEntry** (16 bytes) | the name |
-| 8 | `mkdir` | the path | status only |
+| 22 | `mount` | — | the mount-point path; the backend endpoint rides as the call's **capability** | — | — |
-| 9 | `unlink` | the path | status only |
+| 23 | `unmount` | — | the mount-point path | — | — |
-| 10 | `rename` | old path, one `0x00`, new path (`len` = total) | status only |
+| 24 | `mkdir` | — | the path | — | — |
+| 25 | `unlink` | — | the path | — | — |
+| 26 | `rename` | — | old path, one `0x00`, new path | — | — |
+| 27 | `bind` | — | the contract name; the provider's endpoint rides as the call's **capability** | — | — |
 
 Notes per operation:
 
 - **open** — the path is the mount-relative path `fs_resolve` handed back
-  (absolute-shaped: `/notes.txt` under fat's `/mnt/usb` mount). Bare names
+  (absolute-shaped: `/notes.txt` under fat's `/volumes/usb` mount). Bare names
   (`greeting`) resolve nowhere — the flat ramfs is retired, and `fs_resolve`
   refuses non-absolute paths. The returned `node` is the *backend's* own
   open-node id: with the router in the kernel there is no forwarding table,
-  and clients hold backend ids directly (see *Lifetimes and trust*).
+  and clients hold backend ids directly (see *Lifetimes and trust*). Every
+  later packet carries it in `Header.target` — the path is spoken once, here,
+  and integers do the rest.
 - **read / write** — a single exchange moves at most 224 bytes
-  (`maximum_payload`); the client loops, advancing `offset` by the returned
+  (`maximum_payload`); the client loops, advancing its own offset by what
-  `len`, until done (read) or the slice is written (write). A `write` reply
+  came back, until done (read) or the slice is written (write). A `write`
-  shorter than requested is progress, not an error; a `len` of 0 means no
+  reply shorter than requested is progress, not an error; a count of 0 means
-  forward progress — stop rather than spin.
+  no forward progress — stop rather than spin.
-- **readdir** — `offset` is a **cursor: the entry index**, not a byte
+- **readdir** — `cursor` is the **entry index**, not a byte position. Each
-  position. Each call returns exactly one entry; the client increments the
+  call returns exactly one entry; the client increments the cursor by 1. **A
-  cursor by 1. A reply with `len` 0 is end-of-directory. The directory must
+  `name_len` of 0 is end-of-directory** — the reply's own length cannot say
-  have been opened with the `directory` flag.
+  so, because the envelope always sends the fixed reply part. The directory
+  must have been opened with the `directory` flag.
 - **mount / unmount** — RETIRED from the wire: mounting is the `fs_mount`
   syscall now (a filesystem server passes its endpoint handle; possession is
-  the capability, exactly the trust of the old cap-passing op). The op
+  the capability, exactly the trust of the old cap-passing op). The verb
   numbers stay reserved. Mount-prefix semantics are unchanged: prefixes
-  match at path boundaries only (`/mnt/usb` never captures `/mnt/usbextra`),
+  match at path boundaries only (`/volumes/usb` never captures
-  the longest matching prefix wins, and an optional backend-side rewrite
+  `/volumes/usbextra`), the longest matching prefix wins, and an optional
-  prefix maps a mount into the backend's namespace (fat serves `/mnt/usb`
+  backend-side rewrite prefix maps a mount into the backend's namespace (fat
-  from its volume root and `/var` from its `/var` subtree).
+  serves `/volumes/usb` from its volume root and `/system/logs` from its
+  `/system/logs` subtree).
 - **rename** — same-directory rename only: the backend compares the old and
   new parent paths and refuses a mismatch. The client (`file_system`) refuses
   earlier when the two paths resolve to different backend endpoints, but that
   check is coarser than "one mount" — one endpoint can serve several mounts
-  (fat serves `/mnt/usb` and `/var`), so a cross-mount rename reaches the
+  (fat serves `/volumes/usb`, `/system/configuration` and `/system/logs`), so
-  backend and fails on its same-directory check.
+  a cross-mount rename reaches the backend and fails on its same-directory
+  check.
+- **bind** — the protocol registry's claim verb, implemented only by the
+  synthetic `/protocol` backend inside PID 1
+  ([protocol-namespace.md](../os-development/protocol-namespace.md)). A file
+  backend answers `-ENOSYS`.
 
 ## Open flags
 
-Bitwise OR in `Request.flags`, meaningful for `open` only:
+Bitwise OR in `open`'s `flags`, meaningful for `open` only:
 
 | bit | name | meaning |
 |----:|------|---------|
@@ -129,7 +154,7 @@ Bitwise OR in `Request.flags`, meaningful for `open` only:
 | 2 | `directory` | open a directory node for `readdir` rather than a file |
 | 4 | `truncate` | truncate an existing file to zero length on open (replace, don't overwrite in place) |
 
-## FileStatus — 24 bytes (the `status` reply payload)
+## FileStatus — 24 bytes (the `status` reply's fixed part)
 
 | offset | size | field | meaning |
 |-------:|-----:|-------|---------|
@@ -138,19 +163,19 @@ Bitwise OR in `Request.flags`, meaningful for `open` only:
 | 12 | 4 | — | padding |
 | 16 | 8 | `mtime` | modification time, Unix epoch seconds UTC; 0 if the backend keeps none |
 
-## DirectoryEntry — 16 bytes + name (the `readdir` reply payload)
+## DirectoryEntry — 16 bytes + name (the `readdir` reply)
 
 | offset | size | field | meaning |
 |-------:|-----:|-------|---------|
 | 0 | 4 | `kind` | a **NodeKind** value |
-| 4 | 4 | `name_len` | length of the name that follows |
+| 4 | 4 | `name_len` | length of the name that follows; **0 means end of directory** |
 | 8 | 8 | `size` | the entry's size in bytes |
 | 16 | `name_len` | name | the entry's name, not NUL-terminated |
 
 ## NodeKind
 
-Aligned to the FSH file-type table
+Aligned to the node-kind table in the file-system hierarchy
-(docs/danos-file-system-hierarchy-FSH.md):
+(docs/file-system-development/file-system-hierarchy.md):
 
 | value | kind |
 |------:|------|
@@ -161,9 +186,25 @@ Aligned to the FSH file-type table
 | 4 | symbolic link |
 | 5 | fifo |
 | 6 | socket |
+| 7 | protocol |
 
 Clients should map unknown values to *regular* rather than reject — the
-table can grow.
+table can grow. Kind 6 (`socket`) keeps its wire value but is retired from
+the design — a named rendezvous point is exactly what a `protocol` node is,
+landed as value 7 with the protocol namespace
+(docs/os-development/protocol-namespace.md). `character_device` (stream
+semantics — the tty/console shape) and `block_device` (raw sector-addressed
+volumes, reserved) remain part of the design.
+
+## An open reply may carry a capability
+
+`open` rides `ipc_call`, whose reply direction can hand back an endpoint
+capability alongside the reply. A file backend never uses it — FAT
+answers with a node id and nothing else — but a **synthetic** backend does:
+opening a `protocol` node returns the provider's endpoint, and possession of
+that endpoint *is* the channel. The convention is per-backend, not
+per-operation, so a client that opens an ordinary file simply receives no
+capability, exactly as before.
 
 ## Lifetimes and trust
 
@@ -171,10 +212,24 @@ Open-node ids live in the backend. A client that dies without closing leaks
 nothing permanently: the backend (the FAT server) subscribes to the kernel's
 published process-exit events (docs/process-lifecycle.md) and releases a dead
 client's handles. The kernel VFS root needs no sweep at all — its node tokens
-are permanent for a boot and carry no open state. Ids are plain integers, not
+are permanent for a boot and carry no open state.
-capabilities — a backend trusts its callers with each other's ids today, which
+
-is acceptable while every client is part of the system image and worth
+Ids are plain integers rather than capabilities, so the backend **scopes them
-revisiting (per-client id namespaces) before third-party binaries arrive.
+to the caller's badge**: an open node belongs to the task that opened it, and
+every verb that names one — read, write, status, readdir, close — is answered
+only for that task. A node id is a small number drawn from a table of
+thirty-two, trivially guessable, and until this rule a backend honoured every
+client's ids from every other client
+(docs/os-development/protocol-namespace.md: *handles must be scoped per
+client — validated against the badge, or drawn from a per-client id
+namespace*).
+
+The refusal is deliberately **identical to absence**: a node that is somebody
+else's answers `-ENOENT`, exactly as one that was never opened, so a prober
+learns nothing about which ids are live — the same discipline the protocol
+namespace applies to a refused open. The owner is a *task*, because the badge
+is: a threaded client uses a node from the thread that opened it, which is
+already the granularity of the exit sweep that releases it.
 
 ## Evolution rules
 
@@ -182,11 +237,15 @@ What a non-Zig implementation may rely on, and what it must not:
 
 - Operation values, flag bits, `NodeKind` values, and struct layouts are
   **append-only and frozen once shipped**. The unit test in
-  `library/protocol/vfs/vfs-protocol.zig` pins a sample of them (the `DirectoryEntry`
+  `library/protocol/vfs/vfs-protocol.zig` pins a sample of them (the
-  size, `NodeKind` 0–1, `Operation` values 0, 4 and 5); this page is the
+  `DirectoryEntry` size, `NodeKind` 0–1 and 6–7, `Operation` values 16–21, 26
-  full record of the frozen values.
+  and 27); this page is the full record of the frozen values.
+  *The one renumbering this contract has had was the rebase onto the envelope
+  (P4a), which moved every verb above the reserved range — a deliberate
+  flag-day across a system with no third-party clients yet, not a precedent.*
 - The 256-byte message ceiling is a property of the current IPC transport,
   not a promise; clients should read `maximum_payload`-shaped limits from the
   reply lengths they actually get (loop-until-done), not hard-code 224.
-- Negative statuses beyond -1 will appear (an errno vocabulary); success is
+- Success is exactly 0, and the negative statuses come from one system-wide
-  exactly 0.
+  errno vocabulary (the kernel's, continued by the envelope) rather than from
+  this protocol.

docs/os-development/communication.md

@@ -0,0 +1,120 @@
+# Communication: the four layers
+
+*Design, agreed 2026-07-31. The model document — the vocabulary and layering
+every other communication document speaks.*
+
+danos separates **what is said** from **how the bytes move**, so that the
+mechanism is replaceable. The shape is a network stack's, cut into four
+layers; a program only ever touches the top two.
+
+```
+L3  namespace   /protocol/... names establishment points          protocol-namespace.md
+L2  protocol    the language: packet schemas, verbs, targets      the envelope, library/protocol/*
+L1  channel     two ends exchanging packets and signals           the client library's Channel
+L0  transport   a buffer + a doorbell: moves the bytes            ipc.md (kernel-ipc), later shm-ring, …
+```
+
+## Vocabulary
+
+| Term | Meaning |
+|---|---|
+| **protocol** | The language: which packets exist, what their fields mean, which verbs a provider answers. Defined transport-independently in a `library/protocol/*` module. |
+| **channel** | An open conversation between two processes, speaking one protocol. Established by opening a `/protocol/...` name; both ends can send and receive. |
+| **packet** | The unit a protocol transmits: a bounded, atomic header+payload. Never fragmented — if it doesn't fit, it isn't a packet; bulk data rides shared memory with a packet as the doorbell. |
+| **signal** | A payload-less poke below the packet layer: "something happened, come look." Coalescing — the count may collapse, the fact may not. |
+| **transport** | What moves the bytes of one channel: a buffer plus a doorbell. Chosen (and upgradable) at establishment, invisible above L1. |
+| **endpoint** | A termination point where a transport delivers. The kernel-ipc transport's endpoint is its kernel mailbox object. |
+
+## Addressing: parties by channel, objects by target
+
+There are no network-style addresses in a packet. The two questions addresses
+answer are answered at different layers:
+
+- **Who am I talking to?** The **channel**, decided once at establishment.
+  Opening `/protocol/input` yields a channel; every packet sent on it goes to
+  the peer. Nothing to route per-packet — like TCP, where no HTTP request
+  carries the server's IP.
+- **Who sent this?** Attached to every received packet **by the channel
+  layer**, from identity the transport can verify — under kernel-ipc, the
+  kernel-stamped badge. The sender never writes a source field, which is what
+  makes source unforgeable (the property a network's spoofable source header
+  lacks).
+- **Which of your things?** The packet's **`target`** field: *object*
+  addressing within the already-chosen peer — the vfs protocol's node id, the
+  display protocol's layer id, a block volume. `target = 0` addresses the
+  provider itself; a protocol without objects never uses it.
+
+`target` is how instance multiplicity stays out of the namespace. Ten USB
+sticks and the namespace still holds exactly one name, `/protocol/block`: a
+channel to the provider, `enumerate` lists the current volumes as targets, a
+`targets_changed` signal announces hotplug, and a read names its volume in
+`target`. The unix `/dev/sda`,`/dev/sdb` problem is dissolved, not renamed.
+
+If a future transport genuinely routes between machines, *it* carries real
+source/destination addressing internally at L0 — the way IP runs under TCP —
+and none of it surfaces into the packet header. Protocols stay ignorant of
+distance.
+
+## The transport (L0): a buffer and a doorbell
+
+Strip any transport to its skeleton and the same two parts remain:
+
+| Transport | Buffer | Doorbell | Status |
+|---|---|---|---|
+| **kernel-ipc** | kernel-owned mailbox (the `Endpoint`) | the scheduler (rendezvous wake) | the first transport — [ipc.md](../device-driver-development/ipc.md) |
+| **shm-ring** | user-owned shared-memory ring | a signal | exists ad hoc (display bulk); to be formalized — the unlock for the 256-byte ceiling |
+| network | NIC queue | an interrupt | someday, when danos networks |
+
+Transports differ in their **properties**, which the channel layer exposes and
+the protocol layer may depend on:
+
+- **packet ceiling** — kernel-ipc: 256 bytes request/reply, 64 pushed. An
+  shm-ring's ceiling is its slot size. Kernel-ipc's 256 is the *floor* every
+  protocol may assume everywhere.
+- **synchrony** — kernel-ipc's call is a rendezvous: natural backpressure, no
+  queue to size. An asynchronous transport buffers, so a channel over one
+  needs explicit flow control. Backpressure is a *transport property*, not a
+  channel guarantee — protocols that rely on it say so.
+- **droppability** — pushed event packets may drop when a ring fills;
+  request/reply may not.
+- **capability carriage** — **only kernel-ipc can move a capability.**
+  Handles are kernel objects; a user-space ring cannot transfer one. So
+  kernel-ipc is always the *establishment and control* transport — channels
+  are born on it, capabilities ride it — even when a channel's data is
+  negotiated onto something fatter.
+
+That negotiation is the upgrade path: a channel starts on kernel-ipc; the
+protocol's handshake may then delegate a shared-memory region (as a
+capability, over kernel-ipc) and move its bulk traffic there. The display
+path already does exactly this by hand; formalizing it in the channel layer
+makes it every protocol's option.
+
+## The channel (L1)
+
+A channel has two ends, and **the ends are peers**: each may send packets,
+each may receive, each may signal. Request/reply is a *pattern* over the
+channel — a send with a correlated receive, which the kernel-ipc transport
+happens to accelerate as a single rendezvous — not the definition of it. The
+event stream (subscribe, then pushes) and the change signal (poke, then
+re-read) are the other two patterns; all three are catalogued in
+[protocol-namespace.md](protocol-namespace.md)'s wiring section.
+
+The channel layer's obligations: deliver packets whole, attach the verified
+source to every receive, expose the transport's properties, and hide the
+transport's mechanics. The client library's `Channel` type is this layer made
+concrete — a program holds channels that speak protocols and never touches a
+raw handle.
+
+## The protocol (L2) and the namespace (L3)
+
+A protocol defines its packets through the envelope — every packet begins
+`{operation, target}`, reserved verbs (`describe`, `enumerate`, `subscribe`,
+`unsubscribe`) mean the same thing in every protocol, and `Define` checks
+every packet against the transport floor at compile time. The full treatment,
+including how names are granted, resolved, and restricted per process, is
+[protocol-namespace.md](protocol-namespace.md).
+
+Establishment points are named by contract — `/protocol/display`, never
+`/protocol/ipc-1` — because the name must outlive the mechanism: a
+transport named in the namespace could never be swapped, which would defeat
+this document's premise.

docs/os-development/discovery.md

@@ -231,8 +231,8 @@ Two consequences of neutrality bind on later work:
 
 - **Cross-firmware surfaces are named by domain, not firmware.** System power is
   a [`power`](power.md) protocol, not an "ACPI events" protocol: on x86 the acpi
-  service registers it, on ARM a PSCI/mailbox service registers the same
+  service binds it, on ARM a PSCI/mailbox service binds the same
-  `ServiceId.power`, and subscribers never learn the difference.
+  `/protocol/power`, and subscribers never learn the difference.
 - **Identity must widen before the fdt service exists.** `DeviceDescriptor`'s
   8-byte `hid` holds an EISA id but cannot hold an FDT `compatible` string
   (`"brcm,bcm2835-aux-uart"`); the identity field grows before the ARM path can

docs/os-development/efi.md

@@ -24,8 +24,9 @@ EFI/BOOT/BOOTX64.efi         <- the "removable media" default for x86-64
 ```
 
 The boot volume is **FHS-shaped** (see the repository-layout note in
-[README.md](../README.md)): `build.zig` installs `boot/efi.zig` (built for the `uefi`
+[README.md](../README.md)): the root `build.zig` compiles `boot/efi.zig` (built
-target) at `EFI/BOOT/BOOTX64.efi` — the one path UEFI firmware fixes — and lays
+for the `uefi` target) and `build/images.zig` places it at
+`EFI/BOOT/BOOTX64.efi` — the one path UEFI firmware fixes — and lays
 the rest out by FHS path: the kernel at `system/kernel`, init at
 `system/services/init`, the pre-packed boot capsule at `boot/system.img`
 ([system-image.md](system-image.md)).

docs/os-development/power.md

@@ -15,9 +15,9 @@ Where the events come from is firmware-specific — on x86 they ride the ACPI SC
 ([acpi.md](acpi.md)); on a Raspberry Pi they would come from PSCI or a mailbox.
 What subscribers want is not: *the lid closed* means the same thing regardless of
 who noticed. So the surface is **domain-named**. There is a `power-protocol`
-module and a well-known `ServiceId.power = 5`; on x86 the **acpi service**
+module and a contract named `/protocol/power`; on x86 the **acpi service**
-registers it, and on ARM a PSCI/mailbox service will register the *same* id.
+binds it, and on ARM a PSCI/mailbox service will bind the *same* name.
-Subscribers call `ipc.lookup(.power)` and never learn which firmware they
+Subscribers open `/protocol/power` and never learn which firmware they
 are on — the neutrality the whole [discovery](discovery.md) migration exists to
 preserve, carried one layer up into a running-system surface.
 
@@ -28,28 +28,43 @@ unchanged.
 ## The protocol
 
 The `power-protocol` module ([library/protocol/power/power-protocol.zig](../../library/protocol/power/power-protocol.zig))
-follows the vfs-protocol pattern — extern-struct messages, a version, reserved
+is defined through the [envelope](protocol-namespace.md), so every packet begins
-fields. Three operations:
+with the folded `Header`. `Header.target` is unused in both directions: the
+provider is the only object either side addresses.
 
-| Direction | Operation | Purpose |
+| Direction | Packet | Purpose |
 |---|---|---|
-| subscriber → service | `subscribe` | receive published events; the subscriber's endpoint rides as the call's **capability** (the input/device-manager pattern) |
+| subscriber → service | `subscribe` (reserved verb 2) | receive published events; the subscriber's endpoint rides as the call's **capability** (the input/device-manager pattern) |
-| init → service | `shutdown` | orderly shutdown's last step: enter S5 (soft off) |
+| init → service | `shutdown` (verb 16) | orderly shutdown's last step: enter S5 (soft off) |
-| service → subscriber | `event` | a published `EventMessage`, delivered as a buffered message (never sent *to* the service) |
+| service → subscriber | one event per kind | a published `Notice`, `ipc_send`t as a buffered packet (never sent *to* the service) |
+
+`subscribe` is not one of this protocol's own verbs: a synchronous call whose
+attached capability is the subscriber's endpoint is exactly what the envelope's
+reserved `subscribe` means everywhere, so power adopts it wholesale. And no
+packet carries a version — the reserved `describe` verb is the version handshake,
+asked once at connect time rather than out of every packet's budget.
 
 Events are published, not polled: like the input service, the service holds
 subscriber endpoints as capabilities and `ipc_send`s each event as a buffered
-message, so a slow or dead subscriber can never wedge the source. The event
+packet, so a slow or dead subscriber can never wedge the source. The table, the
+reserved `subscribe`/`unsubscribe` verbs and the fan-out are the **service
+harness's** (`service.Subscribers`), shared with input and the device manager, so
+the acpi service's own code is the ACPI half only — and a subscriber that dies is
+now swept on its exit notification, where before this service had no sweep at
+all. **The kind is the packet's operation** — one declared event per named kind, exactly as the
+input service delivers one per device class — so a subscriber reads *what
+happened* out of the header rather than out of a tag inside the payload. The
 vocabulary is hardware-neutral:
 
-- `power_button` — the button was pressed (a fixed ACPI event on x86).
+- `power_button` (event 16) — the button was pressed (a fixed ACPI event on x86).
-- `lid`, `ac`, `battery` — the named GPE-driven events.
+- `lid` (17), `ac` (18), `battery` (19) — the named GPE-driven events.
-- `notify` — a device notification that maps to none of the above; its `code`
+- `notify` (20) — a device notification that maps to none of the above; its
-  (the ACPI `Notify` argument) and the notifying device's `hid` say which device
+  `code` (the ACPI `Notify` argument) and the notifying device's `hid` say which
-  and what happened.
+  device and what happened.
 
-An `EventMessage` carries the `event` tag plus `code` and an 8-byte `hid`, so a
+The payload every one of them carries is a `Notice`: `code` plus an 8-byte `hid`,
-generic `notify` is fully described without a second round trip.
+so a generic `notify` is fully described without a second round trip, and the
+four named kinds leave both fields zero because the verb already said it all.
 
 **`shutdown` is authority, not information.** It is the only operation that
 *does* something irreversible, so it is gated: the contract is that only init
@@ -58,7 +73,10 @@ sequence over everything else. The acpi service implements this as a **soft
 gate** — it honors `shutdown` only from a process that is a *subscriber*, and
 init is the one subscriber. That stands in for "only the system supervisor may
 power off" without hard-coding a pid, so it still holds under tests where PID 1
-is not init.
+is not init. The question is asked of the harness's table now
+(`Subscribers.has(sender)`), which is why the harness exposes it: the gate is
+unchanged, including the badge being the whole of it — the badge is
+kernel-stamped, so nothing inside a packet can claim to be init.
 
 ## Orderly shutdown
 

docs/os-development/process-lifecycle.md

@@ -188,9 +188,15 @@ zombie state or privileged snooping:
    state by all along is the id the exit event carries.
 
    Subscription, not broadcast-to-everyone: only processes that asked receive
-   events, the kernel keeps a bounded subscriber table, and delivery is the same
+   events, the kernel keeps a bounded subscriber table (sixteen — a normal boot
-   non-blocking coalescing notification as everything else — a dying process never
+   already fields six, since this is what *every* provider with per-client state
-   waits on its mourners. Subscribing is ungated, like `process_enumerate`: what is
+   releases on), and delivery is the same non-blocking coalescing notification as
+   everything else — a dying process never waits on its mourners.
+   A service does not usually write the sweep itself: the shared service harness
+   subscribes for it and drops a dead task's event subscriptions
+   (`service.Subscribers`), and a provider adds its own handler only for state the
+   harness knows nothing about — open files, layers, device tokens.
+   Subscribing is ungated, like `process_enumerate`: what is
    running (and dying) is not a secret between cooperating processes. Subscribers
    do not receive the exit reason — the filesystem server does not care *why*
    the client died.
@@ -285,6 +291,10 @@ callbacks (`on_terminate`, `on_reload`) for programs that want defaults.
 
 `service` owns the `replyWait` loop and folds every event source — signals,
 child exits, protocol messages — into callbacks, with the vocabulary's defaults:
+it also owns the **subscriber side** of any protocol that declares events
+(`service.Subscribers`: the table, the reserved `subscribe`/`unsubscribe` verbs,
+the fan-out, and the sweep on a subscriber's published exit), so every event
+stream in the system behaves identically.
 `terminate` returns from the loop (clean exit), the common `ping` is answered automatically,
 `reload` is ignored unless overridden. One loop, no locking, nothing reentrant. A
 service author writes domain logic; the lifecycle contract is satisfied by the

docs/os-development/protocol-namespace.md

@@ -0,0 +1,474 @@
+# The protocol namespace
+
+*Design, agreed 2026-07-31. Supersedes the `ServiceId` registry. P1–P3 of the
+migration plan at the end have landed (the envelope, the registry and the
+`ServiceId` flag-day, and restriction stage one); P4 and P5 are the remaining
+work list.*
+
+How a program finds, connects to, and is restricted from the things it talks to.
+Three ideas, kept deliberately separate:
+
+1. **Naming** — a path under `/protocol` names a *contract*, not a service.
+2. **Access** — resolving that path yields an endpoint *capability*; what a process
+   cannot resolve, it cannot reach.
+3. **Transport** — unchanged: packets over channels, moved by whichever
+   transport the channel rides (kernel-ipc first).
+   This document is layers **L3** (the namespace) and **L2** (the protocol
+   and its envelope) of the communication stack;
+   [communication.md](communication.md) owns the model and the vocabulary
+   (*protocol* the language, *channel* the conversation, *packet* the
+   transmitted unit, *signal* the payload-less poke, *transport* the
+   replaceable mechanism), and
+   [ipc.md](../device-driver-development/ipc.md) is the first transport.
+
+## Why ServiceId has to go
+
+Today a service calls `ipc_register(service_id, endpoint)` and a client calls
+`ipc_lookup(service_id)`, where `ServiceId` is a compile-time enum in `abi.zig`
+backed by a flat 16-slot table in the kernel. Three defects, in rising order:
+
+- **Static.** The id space is baked into the ABI at compile time. A third-party
+  program can never introduce a service; the one place danos is *less* dynamic
+  than its own design.
+- **Ungated.** `ipc_register` is callable by any process and *replaces* an
+  existing registration. Any process can hijack `.fat` or `.display` and
+  impersonate it. `ipc_lookup` is equally ambient.
+- **Unrestrictable.** Because lookup is a syscall available to everyone, there is
+  no point at which "this process may not talk to the display" can be enforced.
+  Any future file-access restriction would be bypassable by speaking to the FAT
+  server directly.
+
+## Naming: contracts, not services
+
+`/protocol/<name>` names a protocol — the contract a conversation follows — and
+resolving it connects you to whatever process currently provides that contract.
+The client never cared *which* binary answers; it cares that its messages are
+understood. Naming the contract makes that explicit, and buys:
+
+- **Swappable providers.** Replace the display server; `/protocol/display`
+  routes to the new one; clients notice nothing.
+- **Test fakes.** Spawn a program whose namespace wires `/protocol/display` to a
+  mock. The name promises the protocol; the mock speaks it.
+- **One vocabulary.** The names mirror `library/protocol/`: a program imports
+  the `display-protocol` module, then opens `/protocol/display`. What you
+  compiled against and what you ask the namespace for are the same word.
+
+A leaf names one contract — kebab-case, full words, matching the
+`library/protocol/` module that defines its wire format — and related
+contracts group into directories: `/protocol/networking/ip`,
+`/protocol/networking/bluetooth`. Directories organize *contracts only*;
+they never encode addressing (see below), so a directory appears because a
+domain has several contracts, never because hardware multiplied. The module
+tree mirrors the namespace (`library/protocol/networking/ip` ↔
+`/protocol/networking/ip`), and registrar grants scope naturally to subtrees
+— an application installed at `/applications/foo` can be granted
+`/protocol/applications/foo/...` and nothing above it. `/protocol` is
+top level, beside `/system` and `/applications`, because the boundary it names
+is spoken on both sides: applications talk to protocols as much as the OS does
+(see [file-system-hierarchy.md](../file-system-development/file-system-hierarchy.md)).
+
+**Addressing lives inside the protocol, never in the path.** Which volume, which
+layer, which input device — that is a destination field in the messages, the way
+TCP carries a destination address, and the way danos protocols already work (the
+display protocol multiplexes layer ids; the vfs protocol addresses node ids).
+The namespace answers exactly one question — *may this process speak this
+protocol at all* — so `/protocol/block` is one name no matter how many disks are
+attached. The source address is never in the message either: it is the IPC
+badge, stamped by the kernel per message, unforgeable — a property TCP's source
+address does not have.
+
+`/system/devices` (the device inventory) stays purely informational: facts for
+diagnosis, never a routing mechanism. Unix conflated the two in `/dev`; danos
+does not. You *read about* hardware in `/system/devices`; you *talk to* it
+through `/protocol`.
+
+## Resolution: a protocol node in the VFS
+
+The kernel VFS router already does the hard part: `fs_resolve` matches a mount
+prefix and installs the backend's endpoint capability in the caller's handle
+table. The registry is just a backend mounted at `/protocol` — ring 3, like FAT.
+Connecting is a normal vfs-protocol `open` with one twist in the reply:
+
+```
+client                      kernel router                registry backend
+  │ fs_resolve("/protocol/display")                             │
+  │──────────────────────────▶│ prefix match: /protocol         │
+  │◀── registry endpoint ─────│ (capability installed)          │
+  │ vfs open("display") ──────────────────────────────────────▶│
+  │◀───────────────── Reply + capability = provider endpoint ──│
+  │ ipc_call(provider, display-protocol messages...)            │
+```
+
+Both capability moves use machinery the kernel already has: request-direction
+and reply-direction `send_cap` on `call`/`replyWait`. The vfs protocol needs two
+additions, both append-only:
+
+- `NodeKind.protocol` — a node that names a contract; its `open` establishes
+  a **channel** (delivered as an endpoint capability) instead of returning a
+  file id. The node is the protocol, the channel is the conversation, and the
+  addressing inside the packets decides where within the provider each one
+  lands. `readdir` over `/protocol` lists protocol nodes like any others, so
+  the tree stays browsable for diagnosis.
+- The convention that an `open` reply may carry a capability. File backends
+  (FAT) never use it; synthetic backends (the registry, later the device
+  inventory) do.
+
+The path lookup happens once, at connect time. The hot path — `ipc_call` on the
+cached endpoint — is untouched. A provider crash turns the cached endpoint dead
+(`-EPEER`), and the client's recovery is to re-resolve: the restart story falls
+out of the naming layer for free.
+
+## Registration: the registrar, held by init
+
+The registry backend is **init**. It is already PID 1, already spawns every
+service from its manifest, and already holds the supervision link to each — it
+is the process that *knows* which binary is which. (If init grows
+uncomfortable, the same design lifts into a dedicated registry service that
+init spawns first and delegates to; nothing below changes.)
+
+- **Binding.** A service creates its endpoint and sends the registry a `bind`
+  request with the protocol name as payload and the endpoint attached as the
+  call's capability.
+- **Authorization.** Init's manifest gains a column: the protocols each spawned
+  binary may bind. A `bind` from any process not granted that name is refused
+  (`-EPERM`) — the badge identifies the caller, the supervision records map
+  badge to binary. This is the registrar authority; it never leaves init.
+- **Collision is an error.** A name already bound refuses a second bind — never
+  last-writer-wins. When a provider dies, init (its supervisor) unbinds its
+  names; the restarted instance binds again.
+- **Provenance.** The registry records name → task id → binary path, so a
+  diagnostic listing answers "who serves this?" at a glance:
+
+  ```
+  /protocol/display   pid 12   /system/services/display
+  /protocol/input     pid 7    /system/services/input
+  ```
+
+`ipc_register` and `ipc_lookup` retire; the `ServiceId` enum leaves `abi.zig`.
+The kernel keeps one residual rule: `/protocol` becomes a reserved prefix like
+`/system` — `fs_mount` refuses to shadow it, and init's boot-time mount is the
+only one it will ever hold. (Full gating of `fs_mount` is a separate item on
+the security track; the reserved prefix closes the hole for this namespace
+without waiting for it.)
+
+## Restriction: per-process namespaces, not ACLs
+
+danos has no users and no principals, deliberately. Restriction is therefore
+**delegation**: what a process may open is decided by whoever spawned it, and
+enforcement is absence — a protocol you cannot resolve does not exist for you.
+"Permission denied" and "not found" are the same answer, which is the same
+discipline the device layer already follows: the claim is the capability; here,
+the resolvable name is the capability.
+
+Two stages, deliberately ordered so the useful half lands first:
+
+**Stage one — the registry filters by badge.** Init is both the spawner and the
+registry, so its manifest already knows which binary may *open* which protocols
+(a second manifest column, beside the bind grants). An `open` from a process
+whose binary is not granted that protocol is refused. No new kernel mechanism
+at all; the display driver's view can be narrowed to nothing, a future
+downloaded application's to `display` and `input`, today.
+
+**Stage two — spawn passes the namespace.** `spawn` gains an initial
+capability: the child's connection to *its* registry view, chosen by the
+spawner. A newly spawned process starts with an empty handle table and this one
+handle — its world is whatever its parent wired in. This removes the last
+ambient reach (`fs_resolve` finding `/protocol` globally), lets any supervisor
+— not just init — narrow or fake a child's view (an application launcher
+granting an app only what its manifest declares; a test harness substituting
+every provider), and composes down the supervision tree. Stage one's manifest
+column becomes the *content* of the view init builds, so nothing is thrown
+away.
+
+### A worked example: the microphone prompt
+
+The scenario stage two exists for: an application opens
+`/protocol/audio-input`, and the user should be asked. The supervisor is an
+ordinary user process — an application launcher — and the flow needs no new
+security concepts:
+
+1. The launcher spawned the app with a namespace channel that terminates at
+   **the launcher itself**. The app's whole world is a conversation with its
+   supervisor.
+2. The app's `open("audio-input")` packet lands in the launcher,
+   badge-stamped. The launcher spawned the app, so badge → binary path
+   (`/applications/foo`) is its own supervision record — "remember my choice"
+   needs no identity system.
+3. Grant unknown → the launcher parks the request and shows a prompt (it is a
+   user process with display access; init never does UI). Blocking an open on
+   a human is architecturally fine: opens are connect-time, never hot-path.
+4. **Yes** → the launcher opens `/protocol/audio-input` in *its own*
+   namespace and attaches the resulting channel to the parked reply. The app
+   cannot tell a prompt happened — a consented open is indistinguishable from
+   a direct one, merely slower.
+5. **No** → refuse the open, indistinguishable from "no such protocol" — or
+   hand the app a **fake**: a silence-generating provider. The test-fake
+   mechanism doubles as a privacy feature.
+
+The capability discipline holds throughout: the launcher can only grant what
+it holds — if init never gave the launcher `audio-input`, no prompt can
+conjure it. Consent is delegation flowing down the supervision tree, never a
+global ACL edit. And the provider still sees the app's badge on every packet,
+so a coarser second check at the audio service remains possible.
+
+Two mechanical requirements this scenario pins on stage two:
+
+- **Parked replies.** A prompt takes seconds, and the service loop holds one
+  outstanding reply today — the launcher must park request A, keep serving B
+  and C, and reply to A later (by badge). The kernel already tracks owed
+  replies (that is how death delivers `-EPEER`); multiple parked replies is
+  the extension, in the harness and, if needed, the kernel.
+- **Granted channels are dedicated, hence revocable.** Once the app holds a
+  channel capability, nobody reaches into its handle table — so a
+  prompt-granted channel must be one that can be *killed*: a dedicated
+  endpoint pair (or per-client session at the provider) whose death turns
+  the app's capability into `-EPEER`. Revoking microphone access is then
+  killing that channel, using machinery that already exists.
+
+One adjacent problem, named and deferred: **trusted UI**. The prompt is only
+meaningful if the app cannot draw a convincing fake or overlay the real one —
+a display-layer question (a reserved surface for the supervisor chain), owned
+by the display track, not this one.
+
+Fine-grained restriction *within* a protocol (this process may use volume A but
+not volume B) is not the namespace's job. The capability-shaped answer, when it
+is needed: the supervisor pre-opens a connection scoped to one target and passes
+that connection to the child, which never opens `/protocol/block` at all.
+Delegation again, not ACLs.
+
+## The envelope: one addressing scheme for every protocol
+
+Every protocol module today hand-rolls its `Request`/`Reply` with an
+`operation` first field. That convention becomes a library, so addressing is
+uniform and the rules are enforced by construction rather than by review. New
+module: **`library/protocol/envelope`** (the one protocol-layer module that is
+not itself a protocol).
+
+```zig
+/// Every packet a danos protocol transmits begins with this header.
+pub const Header = extern struct {
+    operation: u32, // the verb; values 0..15 are reserved universal verbs
+    _padding: u32 = 0,
+    /// Object addressing, never party addressing: which of the peer's
+    /// objects this packet operates on — a volume, layer, node, device.
+    /// 0 addresses the provider itself. Parties are addressed by the
+    /// channel; the protocol defines target's meaning; the field's place
+    /// and width are universal.
+    target: u64 = 0,
+};
+
+/// Reserved verbs, answered by every provider.
+pub const operation_describe: u32 = 0; // -> protocol name, version, target kinds
+pub const operation_enumerate: u32 = 1; // -> the current targets, one per reply page
+pub const operation_subscribe: u32 = 2; // capability = the subscriber's endpoint
+pub const operation_unsubscribe: u32 = 3;
+pub const first_protocol_operation: u32 = 16;
+
+/// Every reply begins with this.
+pub const Status = extern struct {
+    status: i32, // 0 or a negative errno
+    _padding: u32 = 0,
+    len: u32 = 0, // payload bytes following the header
+    _padding2: u32 = 0,
+};
+```
+
+A protocol is then *defined through* the envelope, not beside it:
+
+```zig
+pub const Protocol = envelope.Define(.{
+    .name = "display",
+    .version = 1,
+    .operations = &.{
+        .{ .name = "configure_layer", .request = ConfigureLayer, .reply = void },
+        .{ .name = "blit", .request = Blit, .reply = void },
+        ...
+    },
+});
+```
+
+`Define` is comptime and is where the enforcement lives:
+
+- verbs are numbered automatically from `first_protocol_operation`, so no
+  protocol can collide with the reserved range;
+- every packet is size-checked at compile time against the kernel-ipc floor
+  — `packet_maximum` (256) for request/reply, `post_maximum` (64) for event
+  packets. Ceilings are transport properties
+  ([communication.md](communication.md)); the floor is what every protocol
+  may assume on any transport. The errors that today surface as runtime
+  truncation become compile errors, and packets-never-fragment is enforced
+  at the source;
+- the generated type carries encode/decode helpers and a provider-side dispatch
+  table, so a provider answers `describe` automatically and unknown operations
+  with `-ENOSYS` uniformly;
+- the service harness (`library/kernel/service.zig`) accepts the generated
+  dispatch type, which is what makes the envelope *enforced*: a protocol that
+  bypasses `Define` does not plug into the harness.
+
+Universal conventions that ride on the reserved verbs:
+
+- **`describe`** is the version handshake. Version lives in the handshake, not
+  in every message — the 256-byte budget is too small to spend per call.
+- **`enumerate`** is how multi-target protocols expose their targets, and the
+  standard `targets_changed` notification (a notify bit) tells subscribers to
+  re-enumerate — arrival and removal of volumes, layers, devices all take the
+  same shape. Hotplug fits the notification ring far better than a filesystem
+  tree ever did.
+- **Source is the badge.** No protocol defines a "sender" field; the kernel's
+  per-message badge is the only source identity, and providers key per-client
+  state on it.
+
+### Paths resolve once; integers do the work
+
+A rule the envelope makes official: **a path appears in a conversation at most
+once — at resolve or open — and everything after it addresses integers.** The
+namespace resolves `/protocol/display` to an endpoint; a backend's `open`
+resolves a path payload to a node id; from then on every packet carries the
+integer in `target`. Integers compare in one instruction and fit the fixed
+header, and the 256-byte message budget never re-carries path strings on the
+hot path. This is already the system's shape — vfs node ids, display layer ids
+— and the envelope pins it as the required shape for every protocol.
+
+Two integer identities, not to be confused:
+
+- **An open handle** — what vfs `open` returns today: transient, meaningful
+  only within one client's session with one provider, swept when the client
+  exits. Cheap, and all a protocol usually needs. Handles must be **scoped per
+  client** — validated against the badge, or drawn from a per-client id
+  namespace. (Today the FAT server's node ids are guessable small integers
+  honoured across clients; that hole closes with this rule.)
+- **A persistent node identity** — a unix inode number, stable across opens
+  and renames. danos deliberately does not promise this, because FAT cannot
+  deliver it: a FAT file's identity is its directory entry, and rename or
+  truncation moves every candidate anchor. If a future filesystem or a cache
+  layer needs stable identity, that is the backend's promise to make, never
+  the protocol's assumption.
+
+The five existing protocol modules (`vfs`, `display`, `input`, `power`,
+`block`, plus `scanout`, `usb-transfer`, `device-manager`) rebase onto the
+envelope during the migration flag-day. `input-protocol`'s subscribe/publish
+split and `vfs-protocol`'s node addressing both map cleanly (`node` and layer
+ids become `target`).
+
+## Wiring: how conversations flow
+
+The patterns below are channel-layer (L1) shapes; the delivery mechanics are
+the kernel-ipc transport's, described here because it is the transport every
+channel starts on. Kernel-ipc provides exactly three delivery shapes, and
+every one is unicast. An endpoint is a mailbox owned by one process — its
+creator receives; anyone holding its capability sends into it. That direction
+never reverses:
+
+1. **Synchronous call** — request/reply. The kernel parks the caller and
+   `replyWait` delivers the reply straight back, so the provider answers
+   without holding any capability to the client. Badge-stamped, blocking, and
+   the *only* shape that carries capabilities (in the request, and in the
+   reply — which is how a reverse path is bootstrapped).
+2. **Asynchronous send** — an event packet pushed into the receiver's post
+   ring, at most `post_maximum` (64) bytes, no reply owed, never blocks the
+   sender. Strictly one-way: to be pushed to, you must first hand the pusher
+   your endpoint.
+3. **Signals** — payload-less notification bits, below the packet layer,
+   coalescing: "something changed, come look."
+
+A bidirectional link is therefore always **a pair of endpoints**, one per
+direction, each delivered by cap-passing. Three conversation patterns are
+built from these, and the envelope names all three:
+
+- **Request/response** — the synchronous call. The default, and the only
+  place capabilities move.
+- **Event stream** — `subscribe` (a synchronous call whose attached
+  capability is the subscriber's own endpoint), after which the provider
+  pushes events asynchronously; `unsubscribe` or subscriber exit ends it.
+  Listened-to, not blocked-on.
+- **Change signal** — a signal plus re-read: `targets_changed` →
+  `enumerate`. For state whose truth lives with the provider.
+
+**Broadcast is a provider pattern, never a kernel primitive.** The kernel
+does not know subscriber sets — a service does. The input service is the
+model: sources *publish* (a unicast call to the service), the service
+*broadcasts* (a fan-out loop of asynchronous sends over its subscriber list,
+so one dead subscriber can never stall the rest). One fan-out point per event
+domain, owned by the service that defines the event.
+
+The harness owns the machinery: the subscriber table, the dead-subscriber
+sweep (via process-exit notifications), and the fan-out loop — all written by
+hand in `input.zig` today, lifted into the service harness so every protocol
+gets identical semantics. `Define` declares a protocol's events (`.events`),
+and each event type is checked against `post_maximum` at compile time,
+generalizing the assert `input-protocol` already carries.
+
+**Event packets are droppable.** A slow subscriber's ring fills, and the
+provider must not block on it — so an event stream is a hint or a coalescing
+signal, never a ledger. Anything that must not be lost is either re-readable
+state (the change-signal pattern) or bulk data in shared memory with a
+packet as the doorbell, which is how the display path already works — the
+packets-never-fragment rule and this one are the same rule seen from two
+sides.
+
+**Source direction (open point).** Today event sources are *clients*: an
+input driver resolves `/protocol/input` and delivers each event as a
+synchronous `publish` call — one capability, obtained by resolution, covers
+everything, and the badge tells the service exactly who each event came from.
+The inversion — the service subscribing to each driver — would require every
+driver to be individually discoverable and its endpoint ferried to the
+service, machinery whose payoff (the service choosing its sources) the
+namespace already provides more cheaply: only a process granted open on
+`/protocol/input` can publish into it. Sources stay clients for now;
+revisited at restriction stage two, when a supervisor can wire capabilities
+at spawn time.
+
+## What this deliberately does not solve
+
+The wider security track, for which this namespace is the foundation, not the
+whole:
+
+- **File access restriction** — the point of the exercise. The same stage-two
+  namespace mechanism extends from protocol names to file paths: the spawner
+  decides which subtrees resolve. Designed separately once this lands.
+- `fs_mount` gating beyond the reserved prefixes; `system_spawn` gating;
+  `klog_read` being world-readable; backends checking the badge on per-node
+  operations (the FAT server honours node ids across clients today).
+- Kernel hardening items already noted in-tree: SMEP/SMAP and SYSRET
+  canonical-RIP, now designed in [smep-smap.md](smep-smap.md).
+- Pipes/FIFOs for the POSIX layer — a byte-stream object *beside* message IPC,
+  wanted by the Python track, unrelated to naming.
+- **Trusted UI** — a permission prompt an application cannot fake or overlay
+  (see the microphone example). A display-track concern: the supervisor chain
+  needs a reserved surface.
+
+## Migration plan
+
+Flag-day per phase, in the style of the DMA-capability conversion — no
+dual-stack periods, the QEMU suite green at each phase boundary.
+
+**P1 — mechanics, no behavior change.** The `envelope` module with its comptime
+`Define`, unit tests; `NodeKind.protocol` and the open-reply-capability
+convention in `vfs-protocol`; existing protocols untouched.
+
+**P2 — the registry.** Init serves `/protocol` (bind with manifest
+authorization, collision refusal, unbind on provider death, provenance);
+kernel reserves the `/protocol` prefix; every service converts from
+`ipc_register` to `bind`, every client from `ipc_lookup` to resolve-and-open;
+`ServiceId`, `ipc_register`, `ipc_lookup` deleted. Tests: unauthorized bind
+refused, collision refused, provider restart re-binds and a client re-resolves.
+
+**P3 — restriction, stage one.** The open-grant column in init's manifest;
+registry refuses ungranted opens. Test: a fixture process denied a protocol its
+neighbour is granted.
+
+**P4 — protocol rebase.** Existing protocol modules re-expressed through
+`Define`; providers move onto the generated dispatch; `describe`/`enumerate`
+answered everywhere; the conformance test fixture exercises the reserved verbs
+against every registered provider.
+
+**P5 — restriction, stage two.** Spawn's initial capability; namespace views
+built by the spawner; ambient resolution of `/protocol` retired. Includes the
+two requirements the microphone example pins: **parked replies** (a
+supervisor parks an open, keeps serving, replies later by badge) and
+**dedicated, killable granted channels** (revocation = channel death →
+`-EPEER`). Scoped separately — it touches `spawn`, the loader contract, and
+every supervisor — and lands together with the file-path half of namespacing.
+
+The unix-path migration ([file-system-hierarchy.md](../file-system-development/file-system-hierarchy.md#migration))
+is independent of P1–P5 and can land before or after.

docs/os-development/smep-smap.md

@@ -0,0 +1,143 @@
+# SMEP and SMAP — supervisor-mode hardening
+
+*Design, 2026-07-31. Not yet implemented. Companion to
+[protocol-namespace.md](protocol-namespace.md) on the security track — this is
+the hardware half; that is the namespace half.*
+
+Two CR4 bits that make the CPU refuse the two things a kernel should never do
+with user memory:
+
+- **SMEP** (Supervisor Mode Execution Prevention, CR4 bit 20): instruction
+  fetch in ring 0 from a page whose U/S bit says *user* → #PF. Kills the
+  classic ret2usr exploit shape — a kernel bug that redirects control flow
+  can no longer land in attacker-prepared user code.
+- **SMAP** (Supervisor Mode Access Prevention, CR4 bit 21): data read/write
+  in ring 0 to a user page → #PF, unless `EFLAGS.AC` is set. `stac`/`clac`
+  open and close deliberate access windows; danos's design needs no windows
+  at all (below).
+
+Detection is CPUID leaf 7, subleaf 0, EBX bit 7 (SMEP) and bit 20 (SMAP).
+Both bits are per-core state: the BSP and every AP must set them.
+
+## Why, in danos terms
+
+Every syscall argument is an attacker-controlled integer, and several take
+pointers. A kernel bug that dereferences a crafted pointer reads, writes, or
+executes memory of the attacker's choosing — the exact bug class the
+isolation tracks exist to prevent. SMEP/SMAP turn that class from "silent
+compromise" into "immediate, attributable #PF with a kernel RIP in the log."
+
+The second benefit matters as much as the first: **SMAP is a permanent
+tripwire.** Once it is on, any *future* syscall that touches user memory
+directly — instead of going through the checked copy layer — faults the
+first time the QEMU suite runs it. The discipline stops depending on review.
+
+## Where danos already stands
+
+The design is closer than it looks, because the IPC layer was built right:
+
+- **The copy layer is already SMAP-proof.** `copyAcross` and `copyFromUser`
+  (`system/kernel/ipc-synchronous.zig:305,333`) never dereference a user
+  virtual address: they walk the page tables and move bytes through the
+  physmap — kernel mappings throughout. SMAP cannot object.
+- **Syscall entry already clears AC.** `SFMASK = 0x4_0700` clears IF, TF,
+  DF, **AC** on every `syscall`
+  (`system/kernel/architecture/x86_64/per-cpu.zig:76`). The syscall path is
+  SMAP-clean from day one.
+- **The interrupt path is not.** Hardware does *not* clear AC on IDT
+  delivery, and ring 3 can set AC with `popfq` — so a hostile process could
+  take an interrupt with AC=1 and have the handler run with SMAP suspended.
+  `isr_common` (`system/kernel/architecture/x86_64/isr.s:366`) needs a
+  `clac` beside its `swapgs`.
+- **CR4 today:** the BSP inherits firmware CR4 (no kernel write anywhere);
+  APs set PAE/OSFXSR/OSXMMEXCPT in `trampoline.s:62-68`. Neither path sets
+  SMEP/SMAP yet, and both must.
+- **The stragglers.** Nine syscalls still dereference user pointers raw
+  after a bounds check — every one is a SMAP #PF waiting to happen, and
+  every one is *already* a latent kernel fault today (an unmapped-but-in-
+  range user page oopses the kernel instead of failing the call). The
+  verified sweep of `system/kernel/process.zig` (2026-07-31; a
+  whole-kernel `@ptrFromInt` audit found no user-address dereference
+  outside this file):
+
+  | Syscall | Raw access | Direction |
+  |---|---|---|
+  | `system_spawn` | name + argument blob (`:972`, `:980`) | read |
+  | `fs_resolve` | path in (`:1780`), result out (`:1797`) | read + write |
+  | `fs_mount` | prefix + rewrite strings (`:1864`, `:1865`) | read |
+  | `fs_unmount` | prefix string (`:1883`) | read |
+  | `fs_node` | read buffer out (`:1820`) | write |
+  | `debug_write` | message bytes (`:1700`; read twice — memcpy `:1710` and `log.append` `:1717`) | read |
+  | `klog_read` | log bytes out (`:1741`) | write |
+  | `klog_status` | status struct out (`:1758`) | write |
+  | `process_enumerate` | descriptor array out (`:1132`) | write |
+  | `device_enumerate` | descriptor array out (`:388`) | write |
+
+  For the write-direction rows the `@ptrFromInt` is in process.zig but the
+  stores happen in callees (`scheduler.enumerate`
+  `system/kernel/scheduler.zig:1209`, `devices_broker.enumerate`
+  `devices-broker.zig:136`, `log.readAt` `log.zig:209`, the vfs node calls
+  `vfs.zig:257/269/289`) — converting them means bounce buffers plus
+  `copyToUser` around those calls, not just editing the process.zig lines.
+  (Some paths already do it right — the futex word and the device-register
+  descriptor go through `copyFromUser` (`:1087`, `:924`). The write
+  direction has no public helper yet, but the mechanism exists:
+  `copyAcross` with a kernel source is exactly how IPC replies reach user
+  buffers, so `copyToUser` is a mechanical mirror.)
+
+- **One known gap inside the copy layer itself:** the walk checks presence,
+  not the leaf U/S and writable bits (`ipc-synchronous.zig:20-22` flags
+  this). Today that is nearly moot — the user half contains only mappings
+  the kernel itself created for that process — but it must close before
+  shared or copy-on-write mappings exist, and closing it is part of making
+  the copy layer the single trusted door.
+
+## The plan
+
+**H1 — copy discipline (the real work).** A `user-memory` kernel module:
+`copyFromUser` / `copyToUser` (the missing write direction) via the physmap
+walk, with U/S and writable leaf checks closing the in-tree TODO. Convert
+the nine stragglers. This fixes the latent unmapped-page kernel fault on
+its own — it is worth doing even if SMEP/SMAP never shipped. QEMU suite
+green; no behavior change visible to correct programs.
+
+**H2 — SMEP.** A leaf-7 feature probe (the kernel has per-leaf `cpuid`
+helpers in `apic.zig` to generalize); set CR4.SMEP during per-CPU bring-up
+on BSP and APs — prefer the Zig-side per-CPU init over the trampoline
+assembly, so one code path covers every core and the trampoline stays
+minimal. Audit first that ring 0 never executes user-mapped pages: kernel
+text lives in the kernel half, `jump_to_user` is kernel code, and the AP
+trampoline page is kernel-mapped — expected clean, verify before flipping.
+
+**H3 — SMAP.** Add `clac` at `isr_common` entry. `clac` is #UD on CPUs
+without SMAP, so the instruction is a 3-byte NOP in the image, patched to
+`clac` at boot when CPUID advertises SMAP (one-time patch beats a
+conditional branch in the hottest path in the kernel). Then set CR4.SMAP in
+the same per-CPU init. From this point the whole QEMU suite doubles as the
+enforcement test: any missed raw dereference is a vector-14 with a kernel
+RIP and a user CR2 — loud and attributable.
+
+**H4 — keep it honest.** A line in the coding standards: kernel code
+touches user memory only through `user-memory`; there is no `stac` anywhere
+in the tree, and a PR that adds one is wrong by definition. SMAP enforces
+the rule mechanically at test time.
+
+Feature-gating follows the timekeeping rule (work on any VM, real Intel,
+real AMD): both bits are probed, absence is logged and tolerated — like the
+IOMMU's fail-open, the machine still boots, just unhardened. QEMU: TCG
+implements both; KVM inherits the host (Intel Ivy Bridge+ for SMEP,
+Broadwell+ for SMAP; AMD Zen+ for both). The test images should run with
+`-cpu max` so the suite always exercises the enabled paths.
+
+## Adjacent, deliberately separate
+
+- **SYSRET canonical-RIP hardening** (`isr.s:192-194` documents it): a
+  non-canonical return RIP makes `sysretq` #GP *in ring 0* on Intel. Same
+  hardening bucket, independent fix (validate RCX before `sysretq`, fall
+  back to `iretq`), should ride the same branch as H2/H3 but is not
+  SMEP/SMAP.
+- **KPTI / Meltdown-class leaks are out of scope.** SMEP/SMAP police
+  architectural accesses, not speculative ones. danos runs one kernel
+  mapping in every address space and accepts that on affected hardware;
+  revisit only if the threat model ever includes hostile native code on
+  shared machines.

docs/os-development/system-image.md

@@ -11,7 +11,7 @@ sequential pass and hands the bytes to the kernel unmodified.
 
 The capsule is a *performance artifact*, not a source of truth. The boot
 volume's `/system` and `/test` file trees remain the canonical layout (see
-[danos-file-system-hierarchy-FSH.md](../file-system-development/danos-file-system-hierarchy-FSH.md));
+[file-system-hierarchy.md](../file-system-development/file-system-hierarchy.md));
 the capsule is a pre-baked snapshot of the same binaries, derived from the same
 build graph, so the running system is identical whether the loader read the
 capsule or walked the tree.
@@ -36,11 +36,11 @@ so it need be no fancier. Little-endian throughout:
 
 ```
 Header        magic: u32 = "DNR2" (0x32524E44), count: u32
-Entry × count name: [64]u8 (NUL-padded FHS path), offset: u64, len: u64
+Entry × count name: [64]u8 (NUL-padded hierarchy path), offset: u64, len: u64
 blobs...      each entry's file bytes, at its offset within the image
 ```
 
-- **Names are full FHS paths** (`/system/services/init`), not basenames — that
+- **Names are full hierarchy paths** (`/system/services/init`), not basenames — that
   is what "v2" means. The 64-byte capacity matches `abi.maximum_process_name`,
   so a task named after its binary path is never truncated. Paths longer than
   63 bytes are a build error (`pack-system-image.py` rejects them).
@@ -54,14 +54,14 @@ blobs...      each entry's file bytes, at its offset within the image
 
 ## How it is built
 
-`build.zig` maintains one `bundled` list — every user binary and its FHS home.
+`build.zig` maintains one `bundled` list — every user binary and its hierarchy home.
 Three artifacts are derived from that same list, in the same build graph, so
 they cannot drift apart:
 
-1. **The tree**: each binary installed at its FHS path (`zig-out/system/...`
+1. **The tree**: each binary installed at its hierarchy path (`zig-out/system/...`
    and `zig-out/test/...`, mirrored onto the FAT boot volume by
    `tools/make-fat-image.py`).
-2. **The manifest** (`system/manifest`): the FHS path of every bundled binary,
+2. **The manifest** (`system/manifest`): the hierarchy path of every bundled binary,
    one per line — the loader's per-file fallback input.
 3. **The capsule**: `tools/pack-system-image.py` packs the same binaries into
    the v2 container, installed at `zig-out/boot/system.img` and placed on the
@@ -103,7 +103,7 @@ the kernel (`kernel.zig`) then publishes the same bytes twice, to two
 consumers:
 
 - **The process layer** (`process.zig`): `system_spawn` looks binaries up in
-  the ramdisk via `Reader.find` — exact FHS path, or unique basename for
+  the ramdisk via `Reader.find` — exact hierarchy path, or unique basename for
   pre-path callers — and loads them as fresh ring-3 processes. The stored path
   becomes the task's name.
 - **The VFS root** (`vfs.zig`, `setInitialRamdisk`): the image is mounted as
@@ -111,7 +111,7 @@ consumers:
   paths, so `/system` and, when the fixtures are bundled, `/test`. Directory
   nodes are derived from the entry paths (the unique parents), so the trees
   are listable and their files readable over the normal VFS protocol — the
-  FHS boot tree every process sees comes straight out of the capsule bytes.
+  boot tree every process sees comes straight out of the capsule bytes.
 
 The image is never copied after the handoff and never mutated: the initrd is
 immutable, which is what makes the VFS's node serving lock-free.

docs/os-development/threading-plan.md

@@ -22,11 +22,12 @@ lands on its own and ends in a **verifiable gate** — shaped for a `/loop` run,
 ## Conventions
 
 Follow [coding-standards.md](../coding-standards.md): spell out non-acronym abbreviations,
-kebab-case file names, no `Co-Authored-By` trailers. New user binaries go through
+kebab-case file names, no `Co-Authored-By` trailers. New user binaries are
-`addUserBinary` (with the new `threaded` flag where a binary spawns threads) and get
+packages whose build.zig calls `build_support.userBinary` (with `.threaded =
-packed into the initial-ramdisk; new syscalls extend [abi.zig](../../system/abi.zig)
+true` where a binary spawns threads) and get packed into the initial-ramdisk;
-`SystemCall` + a `library/runtime` wrapper; test services live beside the code they
+new syscalls extend [abi.zig](../../system/abi.zig) `SystemCall` + a
-exercise and register a `ServiceId` if they must be looked up.
+`library/kernel` wrapper; test services live beside the code they exercise and
+bind a `/protocol/test/...` name if they must be reachable.
 
 ## How to verify along the way
 

docs/os-development/threading.md

@@ -61,9 +61,10 @@ runtime — rebuilt in lockstep — knows the mapping.
    backend would either bake danos syscall numbers into std (breaking ABI privacy and
    renumbering) or fork std to route back through the runtime — a permanent rebase
    cost that buys nothing the native type doesn't.
-2. **Our user binaries are built `single_threaded = true`** ([build.zig](../../build.zig)
+2. **Our user binaries are built `single_threaded = true`** (the shared recipe in
-   `addUserBinary`), which compiles threading out entirely and makes atomics and TLS
+   [build-support/build.zig](../../build-support/build.zig)), which compiles threading
-   single-threaded. Threads need this flipped per binary regardless.
+   out entirely and makes atomics and TLS single-threaded. Threads need this flipped
+   per binary regardless.
 
 So we take the *shape* of `std.Thread`, not the *type*. The cost of replicating the
 surface (spawn/join/Mutex/Condition) is small; the cost of the std type is the ABI
@@ -236,9 +237,10 @@ see the intro). Two scoped pieces, as built:
 
 ### Build: multi-threaded codegen, opt-in
 
-A binary opts in by being added with `addThreadedUserBinary` — as `addUserBinary`,
+A binary opts in with `.threaded = true` in its package's
-but the shared implementation builds it `single_threaded = false` — so atomics and
+`build_support.userBinary` call — the shared recipe in build-support then builds it
-(later) TLS are real. Threads and atomics are unsound in a `single_threaded` image,
+`single_threaded = false` — so atomics
+and (later) TLS are real. Threads and atomics are unsound in a `single_threaded` image,
 so a binary must opt in **before** it may call `Thread.spawn`. Everyone else
 stays single-threaded and lean.
 
@@ -268,13 +270,15 @@ stays single-threaded and lean.
   - *Handles do not cross threads.* The handle table lives on the `Task`
     ([scheduler.zig](../../system/kernel/scheduler.zig)), so a handle number is meaningful
     only to the thread that created it — thread A's endpoint handle `3` is not thread B's.
-    A thread that needs to reach an endpoint another thread owns looks it up
+    A thread that needs to reach an endpoint another thread owns opens the name
-    (`ipc.lookup(service)`) to install its **own** handle to the same underlying endpoint.
+    (`channel.openEndpoint("display")`) to install its **own** handle to the same
-    This is how the display's mouse-listener thread reaches the compositor loop's endpoint
+    underlying endpoint — an ordinary client open, with no special mechanism for the
-    to poke it awake (docs/display.md).
+    fact that the provider happens to be this process. This is how the display's
+    mouse-listener thread reaches the compositor loop's endpoint to poke it awake
+    (docs/display.md).
   - *IPC syscalls that touch shared kernel state now serialize under the big kernel lock.*
-    `create_ipc_endpoint`/`ipc_register`/`ipc_lookup` allocate from the kernel heap and
+    `create_ipc_endpoint` allocates from the kernel heap and
-    mutate the global service registry, endpoint refcounts, and handle tables. Those paths
+    mutates endpoint refcounts and handle tables. Those paths
     were unlocked because a single-threaded process could not race itself; a multi-threaded
     one can, from two cores at once. They now take `sync.enter()` like `call`/`reply_wait`/
     `send` already did — the kernel heap has no lock of its own (heap.zig: "every kernel

docs/os-development/vdso.md

@@ -137,15 +137,15 @@ Grouped as `abi.zig` groups them:
 | process | `danos_exit`, `danos_yield`, `danos_sleep`, `danos_spawn`, `danos_process_enumerate`, `danos_process_kill`, `danos_process_exit_reason`, `danos_process_subscribe`, `danos_process_signal`, `danos_signal_bind` |
 | threads | `danos_thread_spawn`, `danos_thread_exit`, `danos_current_core`, `danos_futex_wait`, `danos_futex_wake`, `danos_thread_self`, `danos_thread_join`, `danos_set_thread_pointer` |
 | memory | `danos_mmap`, `danos_munmap`, `danos_dma_alloc`, `danos_dma_free`, `danos_shared_memory_create`, `danos_shared_memory_map`, `danos_shared_memory_physical` |
-| ipc | `danos_endpoint_create`, `danos_ipc_register`, `danos_ipc_lookup`, `danos_ipc_call`, `danos_ipc_reply_wait`, `danos_ipc_send` |
+| ipc | `danos_endpoint_create`, `danos_ipc_call`, `danos_ipc_reply_wait`, `danos_ipc_send` (naming is not a syscall: a provider binds its contract at the registry and a client resolves `/protocol/<name>` — see [protocol-namespace.md](protocol-namespace.md)) |
 | devices | `danos_device_enumerate`, `danos_device_claim`, `danos_device_register`, `danos_mmio_map`, `danos_irq_bind`, `danos_irq_ack`, `danos_msi_bind`, `danos_io_read`, `danos_io_write` |
 | time | `danos_clock`, `danos_wall_clock`, `danos_timer_bind` |
 | diagnostics | `danos_debug_write` (leveled, kernel-stamped records), `danos_klog_read`, `danos_klog_status` |
 | filesystem naming | `danos_fs_resolve`, `danos_fs_node`, `danos_fs_mount`, `danos_fs_unmount` (naming only — file DATA still crosses the vfs-protocol IPC, see below) |
 
 The constants that ride alongside the calls — mmap protection bits, DMA
-flags, notification badge bits, `ExitReason`, `Signal`, well-known service
+flags, notification badge bits, `ExitReason`, `Signal`, `page_size`, the IPC
-ids, `page_size`, the IPC message maximum — move to the public header too:
+message maximum — move to the public header too:
 they are wire values a Rust program needs verbatim. What stays private in
 `abi.zig` is exactly the thing the vDSO exists to hide: the `SystemCall`
 numbers and the trap convention.

docs/python-on-danos-milestones.md

@@ -0,0 +1,192 @@
+# Python on danos: the milestone plan
+
+The execution plan for [python-on-danos.md](python-on-danos.md). That note holds
+the *why* and the design decisions; this one slices the work into milestones with
+concrete deliverables, tests, and exit criteria. Milestones are numbered **P0–P5**
+(track-local — the global M-series stays with the driver/lifecycle tracks).
+
+Dependencies at a glance:
+
+```
+P0 toolchain + mini-libc ──┐
+P1 streams + console + seam ─┴─→ P2 CPython minimal ─→ P3 terminal + REPL
+                                        │                    │
+                                        └─→ P4 danos module  │
+                                             + Python service│
+P5 process control + shell ←─────────────────────────────────┘
+```
+
+P0 and P1 are independent of each other and can proceed in parallel. P1 is shared
+work — it is also Zig self-hosting Phase 1 and the first three slices of
+[character-devices-and-tty.md](character-devices-and-tty.md).
+
+## P0 — Toolchain + the C library compatibility layer
+
+**Goal:** a C hello-world, cross-compiled on the host with `zig cc`, runs on danos.
+
+Design and slicing live in
+[c-library-compatibility.md](c-library-compatibility.md): the **libdanos-c**
+sysroot (hand-written danos-native headers + `libc.a`) as a `library/c/` build
+package — pure computation (string, libm, `strtod`, the printf/scanf engines)
+lifted from a vendored, pinned musl subtree; the OS plumbing written in Zig over
+the `runtime` surface (re-targeting `runtime.os` when the Zig track authors it);
+`malloc` over danos `mmap`; a `crt0` bridging the danos entry shim to C `main`.
+Driven by `zig cc -target x86_64-freestanding-none -isystem` (the triple becomes
+`x86_64-danos` if the Zig fork lands first; nothing else changes).
+
+Its five slices (sysroot-skeleton, fd-plumbing, malloc, stdio,
+mathematics-and-time) carry their own tests — host-side oracle suites for the
+computation layer, QEMU cases (`c-hello`, `c-file-io`, `c-stdio`, `c-time`) for
+the plumbing.
+
+**Exit:** `c-hello` and `c-file-io` green in the QEMU suite; host computation
+tests green.
+
+## P1 — Stream nodes, console, and the seam pieces
+
+**Goal:** the shared Phase-1 surface exists: byte-stream stdio, cwd, environment,
+entropy. Design and slicing live in
+[character-devices-and-tty.md](character-devices-and-tty.md); this milestone is
+its slices 1–3 plus three small seam pieces:
+
+- **cwd/chdir** — per-process current directory used by path resolution (the
+  kernel already anchors a VFS root per `fs_resolve`; the cwd is the same idea,
+  process-scoped, with `getcwd`/`chdir` exposed through `runtime` and the libc).
+- **Environment** — spawn carries an environment block; the SysV entry stack's
+  `envp` slot ([sysv.md](os-development/sysv.md)) stops being empty; `getenv`
+  reads it. An empty block stays valid.
+- **Entropy** — a kernel `entropy` syscall (RDSEED/RDRAND with a jitter fallback,
+  mirroring the TSC-reliability posture of not trusting one CPU feature blindly);
+  the libc exposes `getentropy`.
+
+- **Tests.** QEMU: the character-device tests from the tty note (offsetless
+  read/write, blocking read, cooked/raw control round-trip), plus `cwd-basics`
+  (chdir + relative open), `env-roundtrip` (spawn with env, child reads it),
+  `entropy-sane` (nonzero, changing, correct length).
+
+**Exit:** a C program reads a cooked line from fd 0 and echoes it to fd 1 —
+injected key events in, bytes read back through the console's in-memory sink,
+all under QEMU with no hardware involved — and `getcwd`/`getenv`/`getentropy`
+return real answers.
+
+## P2 — CPython, minimal configuration
+
+**Goal:** `python -c 'print(2**100)'` runs on danos under QEMU.
+
+- Pin **CPython 3.13.x**; vendor as `third-party/cpython/` or fetch via the build
+  (decide with the build-packages conventions).
+- Host build-Python of the same version (`--with-build-python`).
+- `config.site` cache for the cross answers; `config.sub` patch so
+  `x86_64-unknown-danos` parses; a small `configure`/`pyconfig` patch set kept as
+  rebasable diffs, WASI-style.
+- `--disable-shared`; static `Modules/Setup`: `posix errno _io _codecs _weakref
+  time math _stat _collections itertools _functools _locale _sre` plus what the
+  interpreter core insists on; threadless build (WASI precedent).
+- `Lib/` on the FAT image under the hierarchy (e.g. `/system/python/lib`);
+  `PYTHONHOME` set accordingly; `.pyc` written with **checked-hash
+  invalidation** (FAT's 2-second mtime granularity makes mtime-based validation
+  lie during fast edit-run cycles).
+- `PYTHONHASHSEED` pinned only if P1's entropy slipped — otherwise real
+  hash randomization from day one.
+- **Tests.** QEMU: `python-expr` (the exit criterion), `python-file` (run a
+  script from FAT, write a file, read it back), then a curated slice of CPython's
+  own suite (`test_int`, `test_float`, `test_io`, `test_dict`) as a
+  longer-running target — the suite is the porting harness.
+
+**Exit:** the four QEMU cases green; the CPython test slice green or with a
+short, documented skip list.
+
+## P3 — Terminal + REPL: the first real application
+
+**Goal:** an interactive `python` REPL in a graphical danos terminal — the
+milestone demo for the OS.
+
+- Depends on the display track's font rendering (its stated next step) — until
+  that lands, the REPL is exercised end-to-end through the pseudo-device
+  harness from P1+P2 (scripted input in, output read back), so P2's exit is
+  never blocked on graphics; the graphical terminal is the *interactive* debut.
+- The terminal application: draws with the UI toolkit / display client, consumes
+  keyboard `InputEvent`s, and — per the tty note's load-bearing decision —
+  **serves the VFS stream protocol itself** to its children, reusing the console's
+  line-discipline library. Spawns `python` with its endpoints as fd 0/1/2.
+- Raw mode + the control set give the REPL line editing; window-size control
+  gives it wrapping.
+- **Tests.** QEMU: scripted terminal session (inject key events, assert rendered
+  or captured output). Real-hardware smoke on the Intel box joins the existing
+  checklist.
+
+**Exit:** typing `2+2` into the terminal on the QEMU GPU target prints `4`.
+
+## P4 — The `danos` extension module + a Python service
+
+**Goal:** Python can speak danos: IPC, capabilities, spawn.
+
+- The `danos` module, **written in Zig against `Python.h`**, statically linked
+  via `Modules/Setup`: endpoints (create/send/receive), capability passing,
+  spawn + exit-notification, and the service bootstrap (announce, supervision
+  handshake) — the same surface Zig services use, re-exposed.
+- UI-toolkit bindings as a second module once the toolkit's API settles.
+- Prototype **one real service in Python** — policy-shaped, not data-plane
+  (candidates: hot-plug policy, a settings service) — speaking an existing wire
+  protocol, supervised by the device manager like any service.
+- **Tests.** QEMU: `python-ipc-echo` (Python service echoes over an endpoint, a
+  Zig client asserts), plus the prototype service's own protocol test.
+
+**Exit:** a Python process runs as a supervised danos service exchanging IPC
+with Zig peers.
+
+## P5 — Process control, then the shell
+
+**Goal:** danos can spawn arbitrary programs with arguments and pipes; a small
+Python shell uses it.
+
+The kernel/VFS cluster a shell forces (any shell, any language):
+
+- **exec-of-path** — spawn an arbitrary VFS path, not a named ramdisk binary;
+- **argv/envp** — carried through spawn onto the child's entry stack (env from
+  P1, argv new);
+- **numeric exit status** — extend the exit record beyond the categorical
+  `ExitReason` (the gotcha the Zig roadmap flagged: `WEXITSTATUS` must be real);
+- **fd inheritance + pipes** — a kernel or service pipe (a character device by
+  the tty note's definition) and spawn-time fd mapping.
+
+Then, in order: `subprocess` enabled in CPython (maps onto spawn + the
+exit-notification endpoint — no fork, Windows-style); a **small Python shell** (a
+few hundred lines over `subprocess` + the console: prompt, argv parsing, pipes,
+cwd) as the forcing function that reveals what job control actually needs.
+
+**Explicitly deferred past P5:** the pthread subset over `thread_spawn`/futex,
+signals-in-libc via M17, termios job control (Ctrl-C to foreground child), and
+**xonsh** — which wants all three and is the arc's endpoint, not a milestone.
+
+**Tests.** QEMU: `spawn-argv-exit` (child echoes argv, exits 42, parent sees
+42), `pipe-through` (parent → child → parent), `python-subprocess`, and a
+scripted shell session.
+
+**Exit:** the Python shell runs `program | program` typed at the terminal and
+reports the exit status.
+
+## Post-P5 outlook
+
+Two tracks continue past this plan, each with its own design doc rather than a
+P-number here:
+
+- **Dynamic libraries** ([dynamic-libraries.md](dynamic-libraries.md), D1–D4) —
+  an application-layer facility (the OS stays static and lean): `dlopen` in the
+  libc, then libffi + `ctypes` + loadable extension modules, then shared
+  read-only mappings so N Python services hold one physical `libpython`.
+- **The full C compatibility layer**
+  ([c-library-compatibility.md](c-library-compatibility.md), stages 2–3) — the
+  standing rule that every system capability ships with its C spelling, draining
+  the absence table toward "portable C builds on danos"; `fork` is the one
+  permanent exception.
+
+## Related
+
+- [python-on-danos.md](python-on-danos.md) — the design note this executes.
+- [c-library-compatibility.md](c-library-compatibility.md) — P0's design.
+- [character-devices-and-tty.md](character-devices-and-tty.md) — P1's design.
+- [zig-self-hosting.md](zig-self-hosting.md) — shares P1; its fork makes P0's
+  triple prettier but gates nothing here.
+- [os-development/process-management.md](os-development/process-management.md) —
+  the spawn/exit surface P5 extends.

docs/python-on-danos.md

@@ -0,0 +1,261 @@
+# Python on danos: the CPython milestone
+
+A design note (not built yet) on bringing **CPython** to danos, compiled with the Zig
+toolchain (`zig cc`). Like [zig-self-hosting.md](zig-self-hosting.md), it is
+forward-looking: it sets a direction and the decisions that follow from it.
+
+## Why Python, and why now
+
+The Zig self-hosting road is gated on a compiler fork and a long std-library seam.
+Python is the **stop-gap that removes the wait**: a working CPython gives danos a way
+to write programs — services, tools, application prototypes — *without* the Zig
+compiler being self-hosted, and it brings the pure-Python package ecosystem along as
+a bonus. The intended division of labour:
+
+- **Zig** — the kernel, drivers, and anything on a data plane (interrupt paths,
+  DMA rings, block I/O). Unchanged.
+- **Python** — the control plane and the prototyping surface: services that are
+  event loops over IPC, policy logic that changes often, application experiments,
+  and eventually the shell.
+
+Python is also the scripting language for the terminal-and-shell arc: the first
+real danos application is planned as a terminal, a terminal wants a shell, a shell
+wants a scripting language — and [xonsh](https://xon.sh) (a shell written in
+Python) marks where that road can end.
+
+### Non-goals
+
+- **No drivers in Python.** Interrupt handling, ring management, and DMA stay in
+  Zig. Python may *supervise and configure* drivers; it does not sit in their hot
+  paths (interpreter overhead and garbage-collection pauses in an interrupt path
+  are disqualifying).
+- **No dynamic loading during bring-up, no `pip`.** The whole arc here ships
+  statically linked. Dynamic libraries are a real *later* milestone
+  ([dynamic-libraries.md](dynamic-libraries.md)) — an application-layer
+  facility that unlocks `ctypes` and loadable extension modules; the operating
+  system itself stays static and lean regardless (the size doctrine below).
+  `pip` stays out either way until a networking track exists.
+- **No fork.** `os.fork` will not exist. This costs almost nothing (see "The
+  spawn model fits").
+
+## The realization that shapes everything: the compiler is not the obstacle
+
+`zig cc` is a full Clang-based C cross-compiler, and CPython is portable C with
+official precedent for stranger targets than danos — the WASI port is upstream
+tier-2, and it runs **without fork, without dynamic loading, and without working
+threads**. Every "CPython can't possibly run there" objection has already been
+answered upstream by a target *more* constrained than danos.
+
+What CPython actually needs is a **C environment**: headers and a `libc.a`. danos
+has neither — and that is the whole project. In the language of the Zig roadmap's
+three doors, this is the **door-2-shaped work** (the deferred "musl door"), not the
+`std.os.danos` seam: CPython never touches Zig's std.
+
+### The same surface, a third time
+
+The Zig roadmap observed that door 1 (`std.os.danos`) and door 2 (a libc) implement
+the *same* ~30 danos-facing operations at different layers. CPython consumes that
+identical surface through C spellings. So nothing here is throwaway: the
+danos-native operations backing `runtime.os` are the same ones the libc bottoms out
+in, and the gaps this track must close (stdio byte streams, cwd, environment,
+entropy) are **exactly the Phase-1 gaps the Zig roadmap already lists**. The two
+tracks share a road until Python forks off at "build the libc."
+
+## Where danos stands: coverage vs. the gaps
+
+Judged against the minimal CPython configuration (static, WASI-like):
+
+| CPython need | danos today | Gap |
+|--------------|-------------|-----|
+| open/read/write/close/lseek, readdir | VFS + FAT via `runtime.fs` | none — wrap in C |
+| mkdir / unlink / rename / truncate | done (self-hosting Phase 2) | none |
+| stat with mtime | done (`wall_clock` + FAT mtime) | none |
+| mmap/munmap (object allocator) | native syscalls | none |
+| monotonic + wall clock | `clock` + `wall_clock` syscalls | none |
+| a place for `Lib/` | FAT boot image | none — better than WASI has it |
+| fork / exec | not needed (subprocess disabled at first) | — |
+| dynamic loading | not needed (static extension modules) | — |
+| getcwd / chdir | — | **missing** (shared with Zig Phase 1) |
+| environment variables | `Init` has no env | **missing** (can start empty) |
+| entropy | — | **missing** (hash seed; `PYTHONHASHSEED` pins it meanwhile) |
+| byte-stream stdin/stdout (fd 0/1/2) | `debug_write` out; structured `InputEvent` in | **missing** (shared with Zig Phase 1; the REPL needs it) |
+| signals | — | stubs suffice (WASI precedent); M17 signals-over-IPC maps on later |
+| threads | native `thread_spawn`/futex | build threadless first; a pthread subset later (xonsh needs it) |
+
+The clustering repeats the Zig roadmap's: **files, memory, and time are done; the
+work is the C packaging plus the small seam pieces** (tty bytes, cwd, env, entropy).
+
+## The libc decision: hand-rolled in Zig, computation lifted from musl
+
+Two viable shapes were considered:
+
+| Option | What it is | Verdict |
+|--------|-----------|---------|
+| **Mini-libc in Zig** | C-ABI-exporting Zig library over `runtime.os`/`runtime.fs`, shipped as headers + `libc.a`. | **Take this.** Reuses the danos-native surface directly; no Linux assumptions to fight. |
+| **Port musl** | Full musl with a danos syscall backend. | Defer, again. musl assumes Linux syscall semantics in places; heavier than the need. |
+
+The trick that makes the mini-libc tractable: musl's `string/`, `math/` (libm —
+CPython needs essentially all of it), and number-conversion layers are **pure
+computation with no syscalls**. Lift those wholesale (MIT-licensed, designed to
+compile standalone) and hand-write only:
+
+- the OS-facing bottom: fds, `mmap`, clocks, `exit`, `getcwd` — thin C-ABI wrappers
+  over `runtime.os`;
+- a `FILE*` stdio layer (buffered, over the fd layer);
+- `malloc` over danos `mmap` (a simple allocator is fine; CPython does its own
+  small-object arena management above it);
+- the headers (`stdio.h`, `stdlib.h`, `string.h`, `math.h`, `errno.h`, …).
+
+Estimate: **100–150 functions**, of which the hard 40% (libm, string, printf/strtod
+cores) are lifted, not written. Correctness hot spots are `strtod`/`dtoa` (Python's
+float repr round-trips through them) — another reason to lift musl's, not improvise.
+
+## C interop: static extension modules, not ctypes
+
+"Python can interface with C libraries" is true on danos with one important
+correction: **`ctypes` does not work at first** — it is built on `dlopen` + libffi,
+both of which arrive only with the [dynamic-libraries](dynamic-libraries.md)
+milestone (D2). Until then the interop story is the other, older one:
+
+- **Extension modules statically linked into the interpreter** via CPython's
+  `Modules/Setup` mechanism (the standard route for embedded/static builds).
+- **Zig speaks C ABI natively**, so danos extension modules are written in Zig
+  against `Python.h` — no C required. Two modules are planned from the start:
+  - **`danos`** — the system module: endpoints, send/receive, capability passing,
+    spawn, exit notification. This is what makes a Python *service* possible: an
+    event loop over IPC, speaking the same wire protocols as Zig services.
+  - **UI toolkit bindings** — the in-progress danos UI toolkit exposed to Python,
+    so application prototypes drive real windows.
+
+The package story follows: **pure-Python packages work** (unpack into
+`Lib/site-packages` on the FAT image); packages with C extensions must be
+cross-compiled and baked into the interpreter — a curated set chosen per image,
+not `pip install`. That is the honest shape of the stop-gap.
+
+## The roadmap
+
+### Phase 0 — Toolchain + libc bring-up
+
+`zig cc -target x86_64-freestanding-none` plus `-isystem` the danos headers and the
+mini-libc archive. No compiler fork required — this track deliberately avoids the
+Zig roadmap's Phase-0 gate (if the fork lands first, the triple becomes a clean
+`x86_64-danos`; nothing else changes). Exit criterion: a **hello-world C program**
+compiles on the host and runs on danos, printing via the libc's `write`.
+
+### Phase 1 — The shared seam pieces
+
+The same list as Zig self-hosting Phase 1, closed once for both tracks:
+
+- fd 0/1/2 as console **byte** streams (output exists as `debug_write`; input is a
+  new small thing — cooked line input first, raw mode when the REPL wants editing);
+- `getcwd`/`chdir`;
+- environment variables (an empty block is a valid start);
+- an entropy syscall or service (until then, builds pin `PYTHONHASHSEED`).
+
+### Phase 2 — Cross-compile CPython, minimal configuration
+
+Pin one CPython release (3.13 — strongest WASI-era cross-compile support). The
+mechanics are well-trodden upstream since 3.11:
+
+- a same-version **build-Python on the host** (`--with-build-python`);
+- a `config.site` cache answering what configure cannot probe cross
+  (`ac_cv_file__dev_ptmx=no` and friends);
+- a `config.sub` patch so `x86_64-unknown-danos` parses;
+- `--disable-shared`, static `Modules/Setup` with a minimal module set
+  (`posix`, `errno`, `_io`, `_codecs`, `time`, `math`, …);
+- `Lib/` shipped on the FAT image; `PYTHONHOME` pointed at it.
+
+Exit criterion: `python -c 'print(2**100)'` runs on danos under QEMU.
+
+### Phase 3 — Terminal + REPL: the first real application
+
+Depends on the display track's font rendering (already its stated next step) and
+Phase 1's tty. A terminal emulator drawing a `python` REPL is the milestone demo:
+interactive, self-evidently real, and it needs **zero** process-control machinery.
+
+### Phase 4 — The `danos` module and Python services
+
+Write the `danos` extension module and the UI-toolkit bindings; prototype one real
+service in Python (a policy-shaped one — e.g. hot-plug policy or a settings
+service) speaking the existing IPC protocols. This is the payoff phase for
+"prototyping a service or application."
+
+### Phase 5 — Process control, then the shell
+
+The shell — any shell, in any language — forces the surface danos has deferred so
+far: **exec-of-path, argv/envp passing, numeric exit status (`WEXITSTATUS`, not the
+categorical `ExitReason`), fd inheritance, and pipes.** That is a kernel/VFS
+milestone cluster of its own. Then, in order:
+
+1. `subprocess` enabled in CPython (maps onto danos spawn — see below);
+2. a **small Python shell** (a few hundred lines over `subprocess` + line input, no
+   job control) — the forcing function that reveals which process-control pieces
+   actually matter;
+3. **explicitly deferred:** a pthread subset over `thread_spawn`/futex
+   (create/join/mutex/condition/thread-locals), signals via M17 signals-over-IPC,
+   termios job control — and then **xonsh**, which wants all three.
+
+### The spawn model fits
+
+One genuinely good alignment: **CPython does not need fork.** `subprocess` maps
+cleanly onto a posix_spawn-style model — exactly what danos has — and the existing
+exit-notification-via-endpoint is a *better* fit for `Popen.wait` than Unix's
+`wait` semantics. `os.fork` simply won't exist, as on Windows, and almost nothing
+in practice cares.
+
+## Risks and gotchas
+
+- **Binary size — and the size doctrine that makes it acceptable.** danos's
+  leanness mandate applies to the **operating system**: the kernel and the system
+  services stay small (the kernel is measured in kilobytes, not megabytes), and
+  nothing in this track changes that — Python never enters the OS layer. An
+  **application** budget is different: a statically-linked CPython with its
+  module set will be tens of megabytes in ReleaseSafe (the measured ~2×
+  safety-check factor compounds it), and that is *allowed* — applications live
+  on the FAT image, not in the kernel's world. It still shapes the image, and it
+  means every Python service shares one interpreter binary + per-service
+  scripts, so the spawn model needs **argv** before "run this .py" works at all.
+- **FAT mtime granularity is 2 seconds.** CPython's `.pyc` cache validation is
+  mtime-based by default; a rapid edit-run cycle can see stale bytecode. Use
+  hash-based `.pyc` invalidation (PEP 552, `--invalidation-mode checked-hash` at
+  freeze time) or accept the quirk during bring-up.
+- **FAT name lookups are case-insensitive.** Long file names preserve case but
+  match insensitively — the same world Python inhabits on Windows/macOS, so
+  importlib copes, but two modules differing only by case cannot coexist on the
+  image.
+- **`strtod`/float repr correctness.** Python's float round-tripping is exacting;
+  lift musl's conversions rather than writing them, and run CPython's float tests
+  early.
+- **Threadless build is load-bearing, initially.** Like WASI, the first builds have
+  no working `threading`. The escape hatch is real (danos has native threads and
+  futexes; a pthread subset is Phase-5 work) but keep the configuration honestly
+  single-threaded until then.
+- **The test suite is the porting harness.** CPython ships its own conformance
+  suite; getting `test_builtin`, `test_int`, `test_float`, `test_io` running on
+  danos early converts "it seems to work" into a checklist. Budget image space for
+  the test `Lib/` tree during bring-up.
+- **Entropy before exposure.** `PYTHONHASHSEED=0` is fine for bring-up and wrong
+  forever; hash randomization exists because attacker-controlled dict keys are a
+  denial-of-service vector. Land the entropy source before any Python service
+  parses external input.
+
+## Related
+
+- [python-on-danos-milestones.md](python-on-danos-milestones.md) — the execution
+  plan (P0–P5) for this note.
+- [c-library-compatibility.md](c-library-compatibility.md) — the mini-libc
+  (libdanos-c) design behind Phase 0.
+- [character-devices-and-tty.md](character-devices-and-tty.md) — the stream-node /
+  console / no-pty design behind Phase 1.
+- [zig-self-hosting.md](zig-self-hosting.md) — the sibling track; shares Phase 1,
+  diverges at the libc.
+- [os-development/syscall.md](os-development/syscall.md) — the kernel ABI the
+  mini-libc bottoms out in.
+- [os-development/vdso.md](os-development/vdso.md) — the public ABI boundary the
+  `danos` extension module wraps.
+- [os-development/sysv.md](os-development/sysv.md) — the entry stack (argv/envp)
+  the spawn-argv work extends.
+- [device-driver-development/ipc.md](device-driver-development/ipc.md) — the IPC
+  surface Python services speak.
+- [file-system-development/file-system-hierarchy.md](file-system-development/file-system-hierarchy.md)
+  — where `Lib/` and `site-packages` land on the image.

docs/security-track-plan.md

@@ -0,0 +1,545 @@
+# Security track execution plan: paths, protocol namespace, SMEP/SMAP
+
+The design is settled in
+[communication.md](os-development/communication.md),
+[protocol-namespace.md](os-development/protocol-namespace.md),
+[file-system-hierarchy.md](file-system-development/file-system-hierarchy.md),
+and [smep-smap.md](os-development/smep-smap.md). This file is the build order
+— one phase at a time, each phase green before the next starts. Delete or
+archive this file when the last milestone lands.
+
+**Context a fresh session should read first:** the four design docs above,
+then this plan's *Settled decisions* section — those decisions came out of a
+full-code grounding pass (2026-07-31) and must not be re-derived or reopened.
+
+**Definition of green, every phase:** `zig build` clean, `zig build test`
+clean, `python3 test/qemu_test.py` passes (existing scenarios plus the
+phase's new ones — record the suite count in the checkbox), and the relevant
+design doc's status/known-gap lines updated in the same commit. Commit per
+green phase, style `area: lower-case declarative summary`, **no co-author
+trailers**. On a suite failure, read
+`zig-out/qemu-test/<case>-failed-serial.log` before changing anything.
+
+**Workflow:** work in a dedicated git worktree on feature branches cut from
+`main` (one branch per milestone group as marked below); when a group's
+phases are all green, merge to `main` and push. The loop marks a phase `[x]`
+in the same commit that lands it.
+
+**Numbering note:** milestones use the design docs' own names (PM, H1–H3,
+HS, P1–P4) — the M-number sequence is left alone (M19–M22 are reserved by
+the logging/USB-lifecycle track).
+
+## Status
+
+**Live state — updated on `main` after every phase, so this file read from a
+plain `main` checkout always tells the truth about where the work is.**
+
+| | |
+|---|---|
+| Working on | **H2** — SMEP (group 4) |
+| Branch carrying it | `feat/security-group-4` (cut next) |
+| On `main` | everything through P4c — groups 1, 2 and 3 merged |
+| Awaiting merge | nothing |
+| Suite | 111 cases, all passing |
+| Last updated | 2026-08-01 |
+
+A checkbox below means the phase met its definition of green and was
+committed — on the branch named above, which reaches `main` at the next
+group boundary.
+
+- [x] **Phase 0** — baseline: suite green on `main` (106/106, 2026-07-31; `zig build` + `zig build test` clean at 9a32380), plan committed
+- [x] **PM** — path-migration flag-day (`/etc`→`/system/configuration`, `/var/log`→`/system/logs`, `/mnt/usb`→`/volumes/usb`; vfs carve-out for the two writable `/system` subtrees, FAT's `/var` mount split in two; suite 106/106)
+- [x] **H1** — the `user-memory` module; nine stragglers converted; leaf U/S+W checks (plus physmap-coverage confirmation, so an `mmio_map`'d buffer cannot fault ring 0 — this also closes the same hazard on the IPC path; `fs_resolve`'s out-capacity bound made overflow-safe; suite 107/107)
+- [x] **merge** group 1 → main, push (f3bc23c, 2026-07-31)
+- [x] **P1** — envelope module + `Define`; vfs `NodeKind.protocol` + open-reply-capability; client `Channel` (mechanics only, nothing converted; suite unchanged at 107)
+- [x] **P2** — registry in init; `/protocol` reserved; ServiceId flag-day (11 binds, 17 lookups; `protocol.csv` grants, chain-attested identity, dead-owner rebind; the kernel's endpoint-death sweep generalized off the retired registry; suite 108/108). Three adversarial review rounds closed six defects a green suite had missed: a forged power event could shut the machine down; the ping path leaked a capability per call, first in init and then in the shared harness; supervisor attestation by name was defeated by a laundering deputy; and the kernel let any handle-holder bind signals, timers, exits and IRQs to an endpoint it did not own.
+- [x] **P3** — open grants: `protocol.csv` enforcement, denial test. `onOpen`
+  consults the manifest with the same chain-attested identity a bind uses, and a
+  refused caller gets the *same* answer as one naming a contract nobody bound —
+  `-ENOENT`, no capability, the same reply bytes, no log line, and both questions
+  asked on every open so there is nothing to time. Twenty-seven `open` rows cover
+  the whole live client set. One wrinkle the plan had not foreseen: the driver
+  tree is three deep (device manager → PS/2 bus → keyboard/mouse) and attestation
+  is one hop, so a legitimate grandchild read exactly like a laundering deputy;
+  the manifest gained a third permission, `supervise`, which names an authorized
+  supervising task per contract and is deliberately **open-only**, leaving P2's
+  bind attestation and every refusal it makes untouched (suite 109/109)
+- [x] **merge** group 2 → main, push
+- [x] **P4a** — clean protocols rebased onto `Define` (vfs, block, display, scanout, input; display's one overloaded request split per-operation and its field abuse ended, scanout's bogus 64-byte maximum deleted, directory EOF re-spelled as a nameless entry, input moved onto the service harness; new `protocol-conformance` case asks every reachable provider for `describe` and requires `-ENOSYS` for an undefined verb; suite 110/110)
+- [x] **P4b** — misfit protocols rebased (device-manager, power, usb-transfer; every leading operation byte folded into the header, and with it the `device_id`/`device_token` that followed it — `Header.target` now carries the device in all three. device-manager's own `enumerate`/`subscribe` became the reserved verbs and its three `{status, reserved}` reply structs the envelope's `Status`; `ChildAdded` is one struct under two numbers, a call and an event, landing exactly on the 64-byte push floor. power's kinds became one declared event each, the input protocol's shape, so init reads *what happened* from the header; usb-transfer's control data stage moved to the packet tail in both directions, which made `Status.len` the transferred length and `actual_length` redundant. The two silent-breakage sites — init's byte-offset power parse and acpi's `message[0]` dispatch — are gone, the shutdown badge gate unchanged; three more rows in the conformance table. Suite 110/110)
+- [x] **P4c** — harness subscriber lift + badge-scoped per-client integers (the
+  subscriber table, the reserved subscribe/unsubscribe verbs, the fan-out and the
+  dead-subscriber sweep are `service.Subscribers` now; input, acpi and
+  device-manager deleted three hand-rolled variants and their three different
+  ideas of when a subscriber goes away, standardizing on published exit
+  notifications — acpi had no sweep at all and input polled the process list on
+  every subscribe. The three guessable-id namespaces are scoped to the opening
+  badge: FAT node ids on every verb that names one, xHCI device tokens on open,
+  control, bulk and interrupt_subscribe, display layers on configure, fill, blit,
+  damage and destroy — each refusing a wrong owner with the *same* answer as an id
+  nobody holds. New `badge-scope` case, two processes of one fixture, every
+  refusal paired with a control; suite 111/111)
+- [x] **merge** group 3 → main, push
+- [ ] **H2** — SMEP on every core
+- [ ] **HS** — SYSRET canonical-RIP guard
+- [ ] **H3** — SMAP + boot-patched `clac`; `-cpu max` in the harness; negative tests
+- [ ] **merge** group 4 → main, push
+
+---
+
+## Settled decisions (grounding pass, 2026-07-31 — do not reopen)
+
+These resolve every open wrinkle the code inventory surfaced. Where one
+amends a design doc, the amendment lands in the same commit as the phase
+that implements it.
+
+1. **Every packet — request, reply, and event — begins with the envelope
+   `Header`, exactly as the design says; the header is FOLDED, never
+   stacked.** It absorbs each protocol's existing operation/id fields
+   rather than sitting on top of them, so the two apparent 64-byte-limit
+   offenders fit: `ChildAdded` re-lays to 60 bytes (its packed operation
+   byte and `device_id` become `Header.operation`/`.target`);
+   `InterruptReport` puts `device_token` in `Header.target` and trims
+   inline data 48 → 40 bytes (largest real report today is 8). A
+   headerless-events variant was considered and REJECTED (2026-07-31): it
+   re-invents per-protocol mini-headers and breaks uniform tooling. No
+   design-doc amendment; `Define`'s event check stays ≤ 64 *including*
+   the header.
+2. **Bind/open authorization is chain-attested identity: the
+   kernel-stamped binary name PLUS the supervision chain**, both read from
+   the kernel's process records (`ProcessDescriptor` carries `name` and
+   `supervisor`; init walks the chain with `process_enumerate` — no new
+   protocol). A grant row names the binary *and* the supervisor expected
+   in its chain, so a malicious process re-spawning a granted binary
+   (ungated `spawn`, hostile argv — the confused deputy) is refused: its
+   chain roots at the attacker, not at init or device-manager. Name alone
+   is NOT sufficient — that was considered and rejected (2026-07-31).
+   Pure delegation (device-manager forwarding driver binds as
+   capabilities — "option B") is deliberately deferred to P5, whose
+   spawner-wired namespaces subsume it. Amends protocol-namespace.md's
+   "Authorization" bullet in P2.
+3. **Grants live in a new manifest, `/system/configuration/protocol.csv`**
+   (rows: `binary-path, supervisor, bind|open, protocol-name`, where
+   `supervisor` is the binary expected in the caller's supervision chain —
+   `init` for init's own children, `kernel` for harness-spawned fixtures),
+   not in extra init.csv columns — today every post-path init.csv field is
+   argv, and overloading that is ambiguous. init parses both files.
+   *(P2 spelling: the supervisor column carries the binary exactly as the
+   kernel stamped it, so init's own children say `/system/services/init` and
+   the drivers say `/system/services/device-manager`; `kernel` stays a bare
+   word because a kernel task has no binary. A trailing `*` on any field
+   matches a subtree, which is how decision 4's `/test/` rule is expressed.)*
+   *(Clarification, 2026-08-01: the supervisor column names **the authorized
+   supervising task, matched by identity** — the binary is how the row spells
+   it, but init checks the task id. `kernel` is satisfied only by supervisor
+   id 0 (which only the kernel confers — user `system_spawn` always stamps the
+   caller); init's own path only by this init's task id; any other path only by
+   a task init spawned itself or one the kernel spawned. Matching the supervisor
+   by *name* alone is defeated by a laundering deputy — an attacker runs its own
+   instance of `/system/services/init`, has that spawn `/system/services/input`,
+   and both stamped names satisfy the row while the chain is entirely the
+   attacker's. Walking to the root of the chain does not fix it either, since
+   the laundered chain still roots at the real PID 1.)*
+   *(P3 amendment: a third permission, `supervise`, joins `bind|open`. One-hop
+   attestation cannot express the one three-deep chain in the tree — the device
+   manager starts the PS/2 bus, and the bus starts the keyboard and mouse
+   drivers — and nothing structural tells that chain apart from the laundering
+   deputy, since both are a granted binary spawned by a granted binary. Only
+   policy can: a `supervise` row names the authorized supervising task the way
+   every other row names a claimant (binary, its own supervisor, the contract it
+   concerns), and an `open` row may then name that task in its supervisor
+   column. The delegate is itself attested the ordinary strict way, so the chain
+   still anchors in init or the kernel one hop above it and the recursion stops
+   there. It is **open-only** on purpose — a delegate may vouch for what its
+   children *reach*, never for what they *claim* — so the bind path is
+   byte-for-byte P2's and the laundering-deputy refusal is untouched.)*
+4. **Test fixtures bind under `/protocol/test/...`**, granted to any
+   binary whose path starts `/test/` — the subtree-scoping rule from the
+   design doc, dogfooded. `shared_memory_test` (the borrowed-ServiceId
+   hack) becomes `/protocol/test/shared-memory`; process-test's child gets
+   `/protocol/test/process`.
+5. **Rebind after provider death:** a `bind` hitting an existing binding
+   succeeds only if the current owner process is dead (init checks
+   liveness); otherwise `-EBUSY`. Init also unbinds in `restartChild`
+   before respawning its own children. This preserves collision-refusal
+   while making restart work for providers init does not supervise.
+6. **Cross-thread service access** (the display mouse-listener's
+   per-thread self-lookup, `display.zig:512`): threads resolve and open
+   `/protocol/<name>` like any client — once, at thread startup. No
+   special mechanism.
+7. **The envelope module is `library/protocol/envelope/envelope.zig`**
+   (module name `envelope`) — the one protocol-package module not ending
+   in `-protocol`, because it is not a protocol. Wired as a new
+   `addModule` row in `library/protocol/build.zig` with its host tests in
+   that package's test step.
+8. **The QEMU harness gains `-cpu max`** (in `qemu_args`,
+   `test/qemu_test.py:66-83`) so TCG exposes SMEP/SMAP — without it the
+   enabled paths never execute in CI. Landed in H2 so the flag soaks
+   before H3 depends on it.
+9. **Scenario fixtures that need the registry are init-driven.** Kernel
+   test cases that today spawn providers directly (shared-memory,
+   process-test) either spawn init first or move to init.csv-driven
+   scenario boots — resolved per-case in P2 with the suite as the
+   arbiter.
+   *(P2 resolution: init gained a `registry` argv role — it mounts
+   `/protocol`, reads the grants, and starts no services — and each affected
+   case calls `spawnRegistry(rd)` before its own providers. Every case keeps
+   its own spawn set, so no scenario had to be re-shaped.)*
+10. **The capsule-staleness caveat is documented, not fixed.** On-volume
+    edits to `/system/configuration/*.csv` do not reach the initrd copy
+    the loader boots (capsule shadows tree). Same drift exists today with
+    `/etc`; PM adds the note to file-system-hierarchy.md and moves on.
+
+---
+
+## PM — path-migration flag-day
+
+One commit, everything moves together. The authoritative site inventory is
+the grounding pass; the checklist order:
+
+1. Move repo `etc/` → `configuration/` sources; fix the three CSVs'
+   self-referencing headers (`etc/init.csv:1,12`, `etc/devices.csv:1`,
+   `etc/init-diagnose.csv:1`).
+2. `build.zig:309-311`: bundled entries `etc/...` →
+   `system/configuration/...` (this alone re-shapes the image, manifest,
+   and capsule — `tools/make-fat-image.py` and the EFI loader need
+   nothing; the tree-walk fallback even starts picking the CSVs up, a
+   bonus fix).
+3. `system/kernel/vfs.zig` `mountBackend` (`:332-340`): allow exactly
+   `/system/configuration` and `/system/logs` as backend prefixes beneath
+   the initrd `/system` mount; keep refusing everything else under
+   `/system` and `/test`.
+4. `system/services/fat/fat.zig`: `mount_point` → `/volumes/usb` (`:25`);
+   replace the `/var` mount (`:155`) with two `mountRewritten` calls for
+   `/system/configuration` and `/system/logs`; update the mount log lines
+   (the harness matches them).
+5. `system/services/init/init.zig:76` and
+   `system/services/device-manager/device-manager.zig:48`: open the new
+   CSV paths; update the message strings (`init.zig:77,92`,
+   `device-manager.zig:49,61-63,454`).
+6. `system/services/logger/logger.zig:44`: `base = "/system/logs"`
+   (buffers derive from `base.len` comptime — nothing else changes).
+7. `system/kernel/tests.zig:2808-2810`: exclude `/system/configuration/`
+   from the spawn-everything sweep (the CSVs are not programs).
+8. Tests: `fat-test.zig` and `vfs-test.zig` `/mnt/usb` literals →
+   `/volumes/usb`; harness regexes `test/qemu_test.py:175,211,632,717`.
+9. Comment sweep (init, device-manager, logger, fat, engine, vfs, abi,
+   file-system, csv, device, protocol/device-manager, drivers, acpi,
+   build.zig — full list in the grounding inventory); delete vestigial
+   repo `var/`.
+
+**Test:** no new case — the existing 106 are the test, since fat/logger/
+init/device-manager scenarios all assert the new paths through their
+regexes. Suite stays 106.
+
+## H1 — user-memory copy discipline
+
+New kernel module `system/kernel/user-memory.zig`:
+
+- `copyFromUser` moves from ipc-synchronous.zig (which re-exports or
+  imports it); new `copyToUser(user_as, user_va, source) bool` — the
+  mechanical mirror (kernel-source `copyAcross` already does this for IPC
+  replies at `ipc-synchronous.zig:431,460`).
+- The page walk gains leaf U/S and writable checks: `paging.translateIn`
+  (`architecture/x86_64/paging.zig:513-525`) tests only `present` today —
+  add a flags-accumulating variant (2 MiB leaves included); reads require
+  U/S, writes require U/S+W. Closes the TODO at
+  `ipc-synchronous.zig:20-22`.
+- Convert the nine stragglers (table in smep-smap.md). Read direction is
+  local to `process.zig`; the write direction restructures callees with
+  kernel bounce buffers: `scheduler.enumerate` (`scheduler.zig:1209`),
+  `devices_broker.enumerate` (`devices-broker.zig:136`), `log.readAt`
+  (`log.zig:209`), and the `fs_node` flows through
+  `vfs.nodeRead/nodeStatus/nodeReaddir` (`vfs.zig:257/269/289`).
+
+**Test:** kernel unit coverage in `system/kernel/tests.zig` for
+`copyToUser` bounds/permission refusals; one new QEMU case `user-memory` —
+a fixture passes an unmapped-but-in-range buffer to `klog_read`,
+`process_enumerate`, and `fs_resolve` and asserts `-EFAULT` returns with
+the system still alive (today each would oops the kernel). Suite 107.
+
+## P1 — envelope, vfs additions, Channel
+
+- `library/protocol/envelope/envelope.zig`: `Header` {operation:u32, pad,
+  target:u64}, `Status`, reserved verbs (describe=0, enumerate=1,
+  subscribe=2, unsubscribe=3, protocol verbs from 16), `packet_maximum`
+  = 256 / `post_maximum` = 64 (the floor constants protocols compile
+  against — nothing exports them today), and comptime
+  `Define(.{name, version, operations, events})` generating request/reply
+  types, encode/decode, a provider dispatch table (automatic `describe`,
+  `-ENOSYS` for unknown verbs), and compile-time size checks: 
+  request/reply ≤ 256, each `.events` entry ≤ 64 *including* its Header
+  (decision 1). Host unit tests in the protocol package's test step.
+- `library/protocol/vfs/vfs-protocol.zig`: `NodeKind.protocol = 7`; the
+  open-reply-may-carry-capability convention documented in the module.
+  Rewrite the value-pinning unit test (`:108-117`) to pin the *new*
+  stable values.
+- `library/kernel/file-system.zig` + a new `Channel` type in
+  `library/kernel` (or `library/client`): `open("/protocol/<name>")` →
+  resolve, vfs open, receive the reply capability → a `Channel` wrapping
+  the handle with `call`/typed helpers. Nothing uses it yet — P2 converts
+  the world.
+- Docs: vfs-protocol.md's NodeKind table gains value 7 (no
+  protocol-namespace.md amendment — decision 1 conforms to it as written).
+
+**Test:** host unit tests only (envelope round-trips, size-check compile
+errors via `error` tests, Channel plumbing against a mock). Suite stays
+107.
+
+## P2 — the registry; ServiceId flag-day
+
+The single biggest phase; one branch, may be several commits, green at the
+end of each.
+
+- **init as registry backend** (`system/services/init/init.zig`): a second
+  endpoint (the supervision endpoint's reply-empty loop is unsuitable for
+  a vfs backend); serve vfs `open`/`readdir` over `/protocol` plus the
+  `bind` operation (name payload + capability). Mount `/protocol` before
+  spawning children. Parse `/system/configuration/protocol.csv`
+  (decision 3). Authorization by chain-attested identity (decision 2):
+  badge → kernel process records → binary name **and** supervision chain
+  (walk `supervisor` links) checked against the grant row's expected
+  supervisor. Unbind on child death in `restartChild`; dead-owner rebind
+  rule (decision 5).
+  Provenance: readdir/diagnostics show name → pid → binary path.
+- **Kernel:** reserve `/protocol` — `mountBackend` refuses mounts at or
+  under it once bound, `installMount`'s remount-replace path refuses it,
+  and `fs_unmount` refuses it (`vfs.zig:164-181,332-351`,
+  `process.zig:1879-1889`). First mount wins (init is PID 1).
+- **Harness:** `library/kernel/service.zig` `Callbacks.service:
+  ?abi.ServiceId` becomes a protocol name; the register call (`:49-51`)
+  becomes bind-with-retry via the registry.
+- **Flag-day conversion** — all 11 registration sites and 17 lookup sites
+  from the grounding inventory: providers (input:123, ps2-bus:223,
+  device-manager:569, acpi:193, usb-xhci-bus:676, usb-storage:205,
+  fat:307, display:699, virtio-gpu:550, shared-memory-server:43,
+  process-test:130 → `/protocol/test/...` per decision 4); clients
+  (input-client:53, display-client:28, driver.zig:173, usb.zig:139,
+  block.zig:72+87, ps2-bus keyboard:35 + mouse:34, virtio-gpu:478,
+  display:314+512 (decision 6), acpi:212, init:218+245 — init
+  short-circuits its own registry, shared-memory-client:22,
+  process-test:85, device-list:22, crash-test:32). Retry loops keep their
+  cadence, wrapping resolve+open instead of lookup.
+- **Delete:** `abi.zig:36-37` (syscall ids — leave holes),
+  `abi.zig:287-303` (enum), `process.zig:223-224,314-343`,
+  `ipc-synchronous.zig:41-43,646-664` and the registry sweep in
+  `:121-140`; the wrappers `library/kernel/ipc.zig:33-35,47-50`; comment
+  sweep (irq.zig:50, tests.zig:3744, vdso.md's syscall table, the docs
+  list in the inventory).
+- Kernel-spawned test scenarios made init-driven where they need the
+  registry (decision 9).
+
+**Test:** new QEMU case `protocol-registry`: a fixture asserts (a) bind of
+an ungranted name → `-EPERM`, (b) bind collision with a live owner →
+`-EBUSY`, (c) provider kill → re-resolve reaches the restarted instance.
+Every existing scenario doubles as conversion proof. Suite 108.
+
+## P3 — open grants (restriction stage one)
+
+- `protocol.csv` `open` rows enforced in the registry's `open` handler,
+  same name-based identity as bind. Default rows grant what today's
+  clients need (from the P2 conversion table); a deliberate hole for the
+  test fixture.
+- Docs: protocol-namespace.md stage-one section gets its "landed" line.
+
+**Test:** new QEMU case `protocol-denied`: a fixture granted
+`/protocol/test/shared-memory` but not `/protocol/display` asserts open of
+the first succeeds and the second fails identically to not-found. Suite
+109.
+
+*Landed. Four things the plan did not foresee, recorded because P4 and P5
+inherit them:*
+
+- *`supervise` — decision 3's amendment. The PS/2 keyboard and mouse drivers
+  are started by the PS/2 bus driver, which the device manager started: the
+  tree's one three-deep chain, and one hop deeper than attestation reaches.
+  Nothing structural separates it from the laundering deputy, so the manifest
+  says which delegate is authorized, per contract. Open-only, so P2's bind
+  attestation is unchanged.*
+- *Indistinguishability is a claim about work, not only about bytes. `onOpen`
+  refreshes the process table, identifies the caller, scans the grants and
+  scans the bindings on **every** open and forms one verdict at the end; and
+  it logs nothing on any branch, because `klog_read` is ungated (a line
+  written on one branch is a line the refused caller can read) and a serial
+  line is milliseconds it could time. The operator's diagnosis is the pair the
+  namespace publishes anyway: `readdir /protocol` for what is bound, the
+  manifest for who may reach it.*
+- *The fixture is `protocol-denied-test`, and its scenario boots the **input
+  service** so the forbidden name is genuinely bound — the fixture reads the
+  namespace listing to prove it before asking for it. Without a live provider
+  the case would be comparing two boot races and asserting nothing.*
+- *Two channels stay open by design, named rather than papered over: `readdir`
+  over `/protocol` lists every bound name to anyone (deliberate — the tree is
+  diagnosable), and `/system/configuration/protocol.csv` is world-readable on
+  the `/system` mount. Stage one hides neither the set of contracts nor the
+  policy; what it removes is the **oracle in the reply**, which is what stage
+  two's parked and faked opens depend on.*
+
+## P4a — clean protocols onto Define
+
+vfs, block, display, scanout, input — the modules whose shapes map
+directly (grounding inventory §1,3,4,6,8):
+
+- vfs: `node` → `target`; `Reply.node` (open's result) moves to reply
+  payload — `library/kernel/file-system.zig` decoders change; readdir
+  stays a protocol verb.
+- block: pure renumber; `attach`'s DMA cap rides the call as today.
+- display: the overloaded 40-byte `Request` becomes per-operation structs
+  (attach_scanout's field abuse dies); `layer` → `target`; blit payload
+  grows to 224 bytes.
+- scanout: renumber; drop its bogus `message_maximum=64` (sync floor is
+  256); fix virtio-gpu's hard-coded `service.run(256, …)` to the
+  generated constant.
+- input: subscribe merges into reserved subscribe; publish renumbers;
+  the event re-lays onto the Header folded (operation = event kind,
+  target = 0; 16 + 28-byte payload = 44 ≤ 64); **input moves onto the
+  service harness** (it is the last hand-rolled loop, no ping/terminate
+  compliance today).
+
+**Test:** new QEMU case `protocol-conformance`: a fixture opens every
+registered protocol and asserts `describe` answers (name, version) and an
+unknown verb returns `-ENOSYS`. Existing input/display/fat scenarios prove
+the rebase. Suite 110.
+
+## P4b — misfit protocols onto Define
+
+device-manager, power, usb-transfer (inventory §2,5,7 — the u8-operation
+re-layouts and raw-offset readers):
+
+- device-manager: u8 operations → Header; its enumerate=4/subscribe=5
+  merge into the reserved verbs; `ChildAdded` splits its dual role —
+  request struct and event, both Header-first (folded to 60 B ≤ 64);
+  `ChildRemoved`'s (parent, bus_address) addressing stays payload.
+- power: u8 operations → Header; subscribe merges; **init's raw
+  byte-offset event parsing (`init.zig:171-173`) and acpi's
+  `message[0]` dispatch (`acpi.zig:435-467`) are rewritten against the
+  generated types** — the two silent-breakage sites, called out so the
+  loop treats them as first-class conversions, not collateral.
+- usb-transfer: `device_token` → `target` (already layout-identical);
+  `InterruptReport` re-lays onto the Header (`device_token` → `target`,
+  inline data trimmed 48 → 40 — largest real report is 8); control/bulk
+  budgets re-verified by `Define` (Status absorbs `actual_length`).
+
+**Test:** existing scenarios are the proof (device hot-add, power button,
+USB storage/HID all exercise these wires); the conformance case now covers
+three more providers. Suite 110.
+
+*Landed. Three judgment calls the plan left open, recorded because a reader of
+the wire formats will want them:*
+
+- *`ChildAdded` is 48 bytes, not the 44 the "60 B" estimate assumed: three `u64`s
+  give the struct eight-byte alignment, so 41 bytes of content round up whatever
+  order the fields sit in. The packet is therefore **exactly** 64 — on the push
+  floor, not under it — which `Define` accepts and the module pins in a test. The
+  fields are ordered small-tail-last deliberately, so the slack the rounding pays
+  for is where the small ones live.*
+- *power's events are declared **per kind** (`power_button`, `lid`, `ac`,
+  `battery`, `notify`), not one `event` with the kind in the payload. That is the
+  shape P4a gave input — "the class is the header's operation, so a subscriber
+  reads the kind from the packet rather than from a tag inside the payload" — and
+  it is what makes `Header.operation` carry information here at all. It also kept
+  every call site's spelling: `Protocol.Event` is re-exported as the protocol's
+  own `Event`, with the members it always had.*
+- *the conformance case still checks two providers, and the three new rows report
+  as unbound. All three P4b contracts arrive with the device manager — it is the
+  first, it spawns the discovery service that binds the second, and the xHCI
+  driver that binds the third — so booting one means booting the driver tree, and
+  the fixture takes **one snapshot** of `/protocol`: a scenario whose bound set
+  depends on how far that tree got would make the case's own summary line a boot
+  race. The rows still earn their place — a future scenario that binds one gets it
+  checked with no edit here, and `/test/*` already holds the `open` grant for
+  `device-manager`.*
+
+## P4c — harness subscriber lift + badge scoping
+
+- `library/kernel/service.zig` grows the subscriber table, exit-
+  notification sweep, and fan-out loop declared via `Define(.events)`;
+  input (:33-116), acpi (:67-68,393-406), and device-manager (:155-166)
+  delete their hand-rolled variants. One sweep idiom: exit notifications
+  (fat's pattern), replacing input's process-list polling and acpi's
+  none-at-all.
+- Badge-scoped per-client integers (the guessable-id holes): fat node ids
+  gain owner checks on every operation (`fat.zig:72-76`), xhci device
+  tokens validate sender and sweep on exit (`usb-xhci-bus.zig:66-88,479`),
+  display layers gain an owner field.
+
+**Test:** extend the fat scenario: a second fixture guesses the first's
+node id and asserts refusal; kernel-side unit test for the harness sweep.
+Suite 111.
+
+*Landed. Four things the plan had not foreseen:*
+
+- *One sweep idiom means one more kernel subscriber per provider, and the kernel's
+  published-exit table held **eight**. A normal boot now fields six (fat, input,
+  power, device-manager, display, and one per xHCI controller), so the table grew
+  to sixteen. It is not a table anyone notices until a service silently loses its
+  sweep, which is exactly the failure the old ceiling was two subscriptions away
+  from.*
+- *The device manager hears each of its drivers die **twice** now — it is both the
+  supervisor its spawn named and, through the harness, a subscriber to published
+  exits — and the notify ring delivers the two badges separately. Untreated, one
+  death counted as two: the restart backoff doubled and the crash-loop cap fired
+  at half the deaths it names. `onDriverExit` therefore retires the dead process
+  id before it decides anything, and the second notification finds nothing to act
+  on. (The `driver-restart` and `pci-scan` drills are what would have caught it.)*
+- *Refusal-equals-absence has a corollary for the verbs that **release**: FAT's
+  `close` used to answer 0 for an unknown node, so scoping it had to change that
+  too — a foreign node and a free one both answer `-ENOENT`, or the pair would
+  have been an oracle for which ids are live. The same applies to the harness's
+  `unsubscribe`.*
+- *Ownership is per **task**, not per process, because the badge is: the kernel
+  stamps the sending thread's id, which is already the granularity of the exit
+  sweep that releases the state (a worker thread's death releases the handles that
+  worker opened). Nothing in the tree shares an id across its own threads today;
+  a per-process notion would need the kernel to stamp the leader, and belongs with
+  P5's spawner-wired namespaces if it is ever wanted.*
+
+## H2 — SMEP
+
+- Generalize the cpuid helper (`apic.zig:351-365`, private, subleaf-0) to
+  a shared probe; gate on `cpuid(0).eax >= 7`.
+- Set CR4 bit 20 in `per-cpu.zig:initSystemCall` (or a sibling called
+  from both `cpu.zig:148` and `smp.zig:181` — the one path both BSP and
+  every AP already execute). Log enabled/absent (fail-open, IOMMU style).
+- Harness: add `-cpu max` to `qemu_args` (decision 8).
+
+**Test:** new QEMU case `fault-smep` mirroring the `fault-*` injector
+pattern (`tests.zig:3906-3938`): ring-0 call through a pointer into a
+user-mapped page; expect `page fault (vector 14)` + `error code : 0x11` +
+kernel-half IP, machine reports the exception (deliberate-exception cases
+put the text in `expect`, per `qemu_test.py:189`). Suite 112.
+
+## HS — SYSRET canonical-RIP guard
+
+- `isr.s` syscall exit (`:256`): validate RCX canonicality before
+  `sysretq`; non-canonical → `iretq` fallback (or kill), per the hazard
+  note at `isr.s:192-194`.
+
+**Test:** kernel unit case driving a thread whose return RIP is forged
+non-canonical via the syscall path if constructible cheaply; otherwise the
+review-level proof plus the existing fault cases regression. Suite 112.
+
+## H3 — SMAP
+
+- `clac` patch site at `isr_common` (`isr.s:367`, before the CPL test —
+  ring-0 nesting inherits AC too): assemble a 3-byte NOP, patch to `clac`
+  at boot through the physmap (the `process.zig:1990-1995` /
+  `smp.zig:79-111` precedent), BSP-only before AP bring-up.
+- Set CR4 bit 21 in the same per-CPU init as SMEP.
+- Coding standards: kernel code touches user memory only through
+  `user-memory`; no `stac` anywhere, ever.
+
+**Test:** new QEMU case `fault-smap`: ring-0 deliberate read of a mapped
+user page; expect vector 14 + `error code : 0x1` + kernel IP. And the
+whole suite becomes the tripwire — any missed straggler now fails loudly.
+Suite 113.
+
+---
+
+**Explicitly out of scope** (own tracks, after this plan): P5 restriction
+stage two (spawn's initial capability, namespace views, parked replies,
+dedicated killable channels — needs a design session on the spawn
+contract), file-path namespacing, trusted UI (display track), pipes/FIFOs
+(Python track), `/applications` and its storage, `fs_mount`/`spawn`/
+`klog_read` gating beyond the `/protocol` reserved prefix, KPTI, IPC
+priority inheritance.

docs/system-requirements.md

@@ -95,9 +95,9 @@ hypervisor configured for UEFI firmware and an xHCI USB controller.
 
 | Requirement | Detail | Source |
 |---|---|---|
-| **x86-64, 64-bit only** | Kernel and loader are built exclusively for `x86_64`; the loader rejects any non-x86-64 kernel ELF (`error.WrongArchitecture`). | `build.zig:481`, `boot/efi.zig:622` |
+| **x86-64, 64-bit only** | Kernel and loader are built exclusively for `x86_64`; the loader rejects any non-x86-64 kernel ELF (`error.WrongArchitecture`). | `build-support/build.zig` (`freestandingTarget`), `boot/efi.zig:622` |
 | **Long mode + PAE + NX** | AP trampoline sets `CR4.PAE`, `EFER.LME`, `EFER.NXE`; NX is used in kernel page-table entries. | `system/kernel/architecture/x86_64/trampoline.s:62` |
-| **SSE / SSE2** | Baseline: the compiler emits SSE for ordinary struct copies. Trampoline enables `CR4.OSFXSR` + `OSXMMEXCPT` and clears `CR0.EM`. | `build.zig:477`, `trampoline.s:62` |
+| **SSE / SSE2** | Baseline: the compiler emits SSE for ordinary struct copies. Trampoline enables `CR4.OSFXSR` + `OSXMMEXCPT` and clears `CR0.EM`. | `build-support/build.zig` (`freestandingTarget`), `trampoline.s:62` |
 | **`syscall` / `sysret`** | Primary user↔kernel entry path. `EFER.SCE` enabled; `STAR`/`LSTAR`/`SFMASK` programmed per core. (`int 0x80` exists as a parallel gate.) | `architecture/x86_64/per-cpu.zig:71`, `isr.s:196` |
 | **Local APIC (xAPIC)** | LAPIC accessed via MMIO at `0xFEE00000`. LAPIC ID read as a `u8` — classic xAPIC. **x2APIC is not supported** (no MSR path). | `apic.zig:67`, `apic.zig:646` |
 | **CPUID + RDTSC** | CPUID leaf `0x15` for TSC frequency; RDTSC is the monotonic clock. | `apic.zig:333`, `apic.zig:113` |
@@ -108,7 +108,7 @@ hypervisor configured for UEFI firmware and an xHCI USB controller.
 - **UEFI only.** A custom UEFI application loader is installed to
   `\EFI\BOOT\BOOTX64.efi`. There is **no BIOS, multiboot, or limine** path. The
   loader tolerates UEFI Class-3 machines with no legacy PIC/PIT.
-  (`build.zig:246`, `boot/efi.zig`)
+  (`build/images.zig` — the EFI/BOOT install — and `boot/efi.zig`)
 - **ACPI is the hardware-discovery mechanism.** The RSDP is taken from the UEFI
   configuration table (ACPI 2.0 GUID preferred, 1.0 fallback). Without a valid
   RSDP there is **no device discovery** — no SMP, no IOAPIC routing, no PCI/USB.

docs/testing.md

@@ -12,7 +12,9 @@ There are two layers:
   `system/abi.zig`, `library/device/model/device-abi.zig`) now spans ~26 modules:
   protocol and on-wire definitions (VFS, USB, virtio-gpu), the FAT engine, the
   display compositor, PS/2 and HID decoding, the kernel log ring, and the
-  runtime's `time`/`thread` — the full list is the test step in `build.zig`.
+  runtime's `time`/`thread` — the list is distributed across the library-domain
+  and binary packages' own `test` steps, which the root `zig build test`
+  aggregates (docs/build-packages-plan.md).
   These compile for the host and run natively.
 - **QEMU integration tests** (`python3 test/qemu_test.py`) — boot the real kernel
   and check its behaviour. This is the interesting part.

docs/zig-self-hosting.md

@@ -347,7 +347,7 @@ Two current decisions fall out of this roadmap:
 - [syscall.md](os-development/syscall.md) — the kernel↔runtime ABI `runtime.os` is built on.
 - [sysv.md](os-development/sysv.md) — the entry stack (`argc/argv/envp/auxv`) danos already constructs.
 - [ipc.md](device-driver-development/ipc.md) — the IPC the VFS/FAT operations travel over.
-- [danos-file-system-hierarchy-FSH.md](file-system-development/danos-file-system-hierarchy-FSH.md) — the
+- [file-system-hierarchy.md](file-system-development/file-system-hierarchy.md) — the
   filesystem layout the file surface serves.
 - [coding-standards.md](coding-standards.md) — danos naming (why the compat spellings
   are confined, and now retired).

library/client/build.zig

@@ -0,0 +1,50 @@
+//! The "client" library domain (library/client): userspace-service clients —
+//! they talk to services over IPC, not to the kernel. Client modules end in
+//! `-client` the way wire protocols end in `-protocol`, so a service, its
+//! protocol, and its client never share a name (`display` the service,
+//! `display-protocol` the wire contract, `display-client` a program's view).
+
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    const kernel = b.dependency("kernel", .{});
+    const protocol = b.dependency("protocol", .{});
+
+    const ipc = kernel.module("ipc");
+    const time = kernel.module("time");
+    // Every client reaches its service by name now: resolve `/protocol/<name>`,
+    // open it, and take the provider's endpoint out of the reply
+    // (docs/os-development/protocol-namespace.md).
+    const channel = kernel.module("channel");
+
+    // A client frames its own packets, so it needs the envelope alongside the
+    // protocol whose verbs it speaks.
+    const envelope = protocol.module("envelope");
+
+    _ = b.addModule("display-client", .{
+        .root_source_file = b.path("display/display-client.zig"),
+        .imports = &.{
+            .{ .name = "channel", .module = channel },
+            .{ .name = "envelope", .module = envelope },
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "time", .module = time },
+            .{ .name = "display-protocol", .module = protocol.module("display-protocol") },
+        },
+    });
+    _ = b.addModule("input-client", .{
+        .root_source_file = b.path("input/input-client.zig"),
+        .imports = &.{
+            .{ .name = "channel", .module = channel },
+            .{ .name = "envelope", .module = envelope },
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "time", .module = time },
+            .{ .name = "input-protocol", .module = protocol.module("input-protocol") },
+        },
+    });
+
+    // Standalone `zig build test`, kept for uniformity across the domains (the
+    // root aggregate depends on every domain's test step). The clients have no
+    // host-runnable unit tests yet — they are thin IPC conversation wrappers —
+    // so the step is empty until one grows some.
+    _ = b.step("test", "Run the client unit tests (none yet)");
+}

library/client/build.zig.zon

@@ -0,0 +1,13 @@
+.{
+    .name = .client,
+    .version = "0.0.0",
+    .fingerprint = 0xc74404553e73d4ff, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{
+        // The clients converse over ipc with time-bounded waits.
+        .kernel = .{ .path = "../kernel" },
+        // Each client speaks its service's wire protocol.
+        .protocol = .{ .path = "../protocol" },
+    },
+    .paths = .{""},
+}

library/client/display/display-client.zig

@@ -0,0 +1,165 @@
+//! User-space display client: talk to the display service (query the mode, and — from D3
+//! — create layers, draw, and present) without hand-rolling the IPC. The `runtime.block`
+//! shape: a cached `/protocol/display` open with a boot-race retry, then extern-struct request/
+//! reply marshalling. See system/services/display/ and docs/display.md.
+
+const std = @import("std");
+const channel = @import("channel");
+const envelope = @import("envelope");
+const ipc = @import("ipc");
+const time = @import("time");
+const display_protocol = @import("display-protocol");
+
+const Protocol = display_protocol.Protocol;
+
+/// The display's current mode, as `info()` reports it.
+pub const Info = struct {
+    width: u32,
+    height: u32,
+    pitch: u32, // bytes per row (may exceed width*4; see docs/framebuffer.md)
+    format: u32, // a device-abi DisplayFormat value (0 = rgbx, 1 = bgrx)
+};
+
+/// The service endpoint, looked up once and cached.
+var handle: ?ipc.Handle = null;
+
+/// Open `/protocol/display`, retrying while it comes up (a client races the
+/// service's bind at boot). Returns the endpoint, or null if it never appears.
+fn service() ?ipc.Handle {
+    if (handle) |h| return h;
+    var attempts: usize = 0;
+    while (attempts < 100) : (attempts += 1) {
+        if (channel.openEndpoint("display")) |h| {
+            handle = h;
+            return h;
+        }
+        time.sleepMillis(50);
+    }
+    return null;
+}
+
+/// A reply the compositor answered with, kept whole so the caller can decode the
+/// verb's own fixed part out of it.
+const Answered = struct {
+    packet: [display_protocol.message_maximum]u8,
+    len: usize,
+
+    fn bytes(self: *const Answered) []const u8 {
+        return self.packet[0..self.len];
+    }
+};
+
+/// Send one request (`target` addresses a layer, or 0 for the compositor itself)
+/// and keep the reply. Null when the transport failed or the compositor refused.
+fn transact(
+    comptime operation: Protocol.Operation,
+    target: u64,
+    request: Protocol.RequestOf(operation),
+    tail: []const u8,
+) ?Answered {
+    const h = service() orelse return null;
+    var packet: [display_protocol.message_maximum]u8 = undefined;
+    const framed = Protocol.encodeRequest(operation, target, request, tail, &packet) orelse return null;
+    var answered: Answered = .{ .packet = undefined, .len = 0 };
+    answered.len = ipc.call(h, framed, &answered.packet) catch return null;
+    const status = envelope.statusOf(answered.bytes()) orelse return null;
+    if (status.status != 0) return null;
+    return answered;
+}
+
+/// The display's current mode, or null if the service never came up.
+pub fn info() ?Info {
+    const answered = transact(.info, 0, {}, &.{}) orelse return null;
+    const reply = Protocol.decodeReply(.info, answered.bytes()) orelse return null;
+    return .{ .width = reply.width, .height = reply.height, .pitch = reply.pitch, .format = reply.format };
+}
+
+/// Composite the dirty layers and flush the frame to the screen.
+pub fn present() bool {
+    return transact(.present, 0, {}, &.{}) != null;
+}
+
+/// One selectable display mode.
+pub const Mode = display_protocol.Mode;
+
+/// Fill `out` with the resolutions the display can switch to; returns how many were written
+/// (zero on the GOP floor, or if the service never came up).
+pub fn modes(out: []Mode) usize {
+    const answered = transact(.get_modes, 0, {}, &.{}) orelse return 0;
+    const offered = Protocol.decodeReply(.get_modes, answered.bytes()) orelse return 0;
+    const count = @min(@min(offered.count, display_protocol.max_modes), out.len);
+    for (0..count) |i| out[i] = offered.modes[i];
+    return count;
+}
+
+/// Change the display resolution. Only a native backend that supports mode-setting honours it
+/// (on the GOP floor it returns false); on success the display's `info()` reports the new mode.
+pub fn setMode(width: u32, height: u32) bool {
+    const changed = transact(.set_mode, 0, .{ .width = width, .height = height }, &.{}) != null;
+    if (changed) mode = null; // the cached mode is stale now
+    return changed;
+}
+
+/// The mode, cached after the first `info()` so `color()` doesn't round-trip per pixel.
+var mode: ?Info = null;
+
+fn cachedInfo() ?Info {
+    if (mode) |m| return m;
+    const i = info() orelse return null;
+    mode = i;
+    return i;
+}
+
+/// The native pixel value for an 8-bit-per-channel colour, in the display's format. A
+/// client packs colours through this so it never has to know the byte order itself.
+pub fn color(r: u8, g: u8, b: u8) u32 {
+    const format = if (cachedInfo()) |i| i.format else 0;
+    return display_protocol.pack(format, r, g, b);
+}
+
+/// A handle to a server-owned layer: a positioned, z-ordered surface the client draws
+/// into by command. Create with `createLayer`; drawing and moves take effect on the next
+/// `present`. Coordinates are signed (a layer may sit partly off-screen).
+///
+/// The id is the packet header's `target` on every call below, so it is named once
+/// per request rather than repeated inside one.
+pub const Layer = struct {
+    id: u32,
+
+    /// Fill a rectangle of this layer (layer-local coordinates) with a native `colour`.
+    pub fn fill(self: Layer, x: i32, y: i32, w: u32, h: u32, colour: u32) bool {
+        return transact(.fill_rect, self.id, .{ .x = x, .y = y, .width = w, .height = h, .colour = colour }, &.{}) != null;
+    }
+
+    /// Copy a `w`×`h` tile of native pixels (row-major, little-endian bytes) into this
+    /// layer at (`x`, `y`). The tile rides inline as the request's tail, so `w*h*4` must
+    /// fit `display_protocol.maximum_payload` — the bound the protocol derives from this
+    /// verb's own fixed part, so the check here can never drift from what fits.
+    pub fn blitTile(self: Layer, x: i32, y: i32, w: u32, h: u32, pixels: []const u8) bool {
+        if (pixels.len > display_protocol.maximum_payload) return false;
+        return transact(.blit_tile, self.id, .{ .x = x, .y = y, .width = w, .height = h }, pixels) != null;
+    }
+
+    /// Move / restack / show or hide the layer.
+    pub fn configure(self: Layer, x: i32, y: i32, z: u32, visible: bool) bool {
+        return transact(.configure_layer, self.id, .{ .x = x, .y = y, .z = z, .visible = if (visible) 1 else 0 }, &.{}) != null;
+    }
+
+    /// Mark a rectangle of this layer (layer-local) dirty for the next present — for when
+    /// the layer's pixels changed without a drawing call the compositor already tracked.
+    pub fn damage(self: Layer, x: i32, y: i32, w: u32, h: u32) bool {
+        return transact(.damage, self.id, .{ .x = x, .y = y, .width = w, .height = h }, &.{}) != null;
+    }
+
+    /// Release the layer and its surface.
+    pub fn destroy(self: Layer) bool {
+        return transact(.destroy_layer, self.id, {}, &.{}) != null;
+    }
+};
+
+/// Create a server-owned layer of `w`×`h` pixels at screen (`x`, `y`) with stacking order
+/// `z` (higher is nearer the front), initially visible. Returns a handle, or null.
+pub fn createLayer(x: i32, y: i32, w: u32, h: u32, z: u32) ?Layer {
+    const answered = transact(.create_layer, 0, .{ .x = x, .y = y, .width = w, .height = h, .z = z, .visible = 1 }, &.{}) orelse return null;
+    return .{ .id = (Protocol.decodeReply(.create_layer, answered.bytes()) orelse return null).layer };
+}

library/client/display/display.zig

@@ -1,198 +0,0 @@
-//! User-space display client: talk to the display service (query the mode, and — from D3
-//! — create layers, draw, and present) without hand-rolling the IPC. The `runtime.block`
-//! shape: a cached `.display` lookup with a boot-race retry, then extern-struct request/
-//! reply marshalling. See system/services/display/ and docs/display.md.
-
-const std = @import("std");
-const ipc = @import("ipc");
-const time = @import("time");
-const display_protocol = @import("display-protocol");
-
-/// The display's current mode, as `info()` reports it.
-pub const Info = struct {
-    width: u32,
-    height: u32,
-    pitch: u32, // bytes per row (may exceed width*4; see docs/framebuffer.md)
-    format: u32, // a device-abi DisplayFormat value (0 = rgbx, 1 = bgrx)
-};
-
-/// The service endpoint, looked up once and cached.
-var handle: ?ipc.Handle = null;
-
-/// Look up the display service, retrying while it comes up (a client races its
-/// registration at boot). Returns the endpoint, or null if it never appears.
-fn service() ?ipc.Handle {
-    if (handle) |h| return h;
-    var attempts: usize = 0;
-    while (attempts < 100) : (attempts += 1) {
-        if (ipc.lookup(.display)) |h| {
-            handle = h;
-            return h;
-        }
-        time.sleepMillis(50);
-    }
-    return null;
-}
-
-/// Send one request, receive its reply; true on a zero status. `out` receives the reply
-/// so callers can read `info`/`layer` fields on success.
-fn transact(request: display_protocol.Request, out: *display_protocol.Reply) bool {
-    const h = service() orelse return false;
-    var req = request;
-    var reply: [display_protocol.reply_size]u8 = undefined;
-    const len = ipc.call(h, std.mem.asBytes(&req), &reply) catch return false;
-    if (len < display_protocol.reply_size) return false;
-    out.* = std.mem.bytesToValue(display_protocol.Reply, reply[0..display_protocol.reply_size]);
-    return out.status == 0;
-}
-
-/// The display's current mode, or null if the service never came up.
-pub fn info() ?Info {
-    var reply: display_protocol.Reply = undefined;
-    if (!transact(.{ .operation = @intFromEnum(display_protocol.Operation.info) }, &reply)) return null;
-    return .{ .width = reply.width, .height = reply.height, .pitch = reply.pitch, .format = reply.format };
-}
-
-/// Composite the dirty layers and flush the frame to the screen.
-pub fn present() bool {
-    var reply: display_protocol.Reply = undefined;
-    return transact(.{ .operation = @intFromEnum(display_protocol.Operation.present) }, &reply);
-}
-
-/// One selectable display mode.
-pub const Mode = display_protocol.Mode;
-
-/// Fill `out` with the resolutions the display can switch to; returns how many were written
-/// (zero on the GOP floor, or if the service never came up).
-pub fn modes(out: []Mode) usize {
-    const h = service() orelse return 0;
-    var request = display_protocol.Request{ .operation = @intFromEnum(display_protocol.Operation.get_modes) };
-    var reply: [display_protocol.modes_reply_size]u8 = undefined;
-    const len = ipc.call(h, std.mem.asBytes(&request), &reply) catch return 0;
-    if (len < display_protocol.modes_reply_size) return 0;
-    const answer = std.mem.bytesToValue(display_protocol.ModesReply, reply[0..display_protocol.modes_reply_size]);
-    if (answer.status != 0) return 0;
-    const count = @min(@min(answer.count, display_protocol.max_modes), out.len);
-    for (0..count) |i| out[i] = answer.modes[i];
-    return count;
-}
-
-/// Change the display resolution. Only a native backend that supports mode-setting honours it
-/// (on the GOP floor it returns false); on success the display's `info()` reports the new mode.
-pub fn setMode(width: u32, height: u32) bool {
-    var reply: display_protocol.Reply = undefined;
-    const changed = transact(.{ .operation = @intFromEnum(display_protocol.Operation.set_mode), .width = width, .height = height }, &reply);
-    if (changed) mode = null; // the cached mode is stale now
-    return changed;
-}
-
-/// The mode, cached after the first `info()` so `color()` doesn't round-trip per pixel.
-var mode: ?Info = null;
-
-fn cachedInfo() ?Info {
-    if (mode) |m| return m;
-    const i = info() orelse return null;
-    mode = i;
-    return i;
-}
-
-/// The native pixel value for an 8-bit-per-channel colour, in the display's format. A
-/// client packs colours through this so it never has to know the byte order itself.
-pub fn color(r: u8, g: u8, b: u8) u32 {
-    const format = if (cachedInfo()) |i| i.format else 0;
-    return display_protocol.pack(format, r, g, b);
-}
-
-/// A handle to a server-owned layer: a positioned, z-ordered surface the client draws
-/// into by command. Create with `createLayer`; drawing and moves take effect on the next
-/// `present`. Coordinates are signed (a layer may sit partly off-screen).
-pub const Layer = struct {
-    id: u32,
-
-    /// Fill a rectangle of this layer (layer-local coordinates) with a native `colour`.
-    pub fn fill(self: Layer, x: i32, y: i32, w: u32, h: u32, colour: u32) bool {
-        var reply: display_protocol.Reply = undefined;
-        return transact(.{
-            .operation = @intFromEnum(display_protocol.Operation.fill_rect),
-            .layer = self.id,
-            .x = @bitCast(x),
-            .y = @bitCast(y),
-            .width = w,
-            .height = h,
-            .colour = colour,
-        }, &reply);
-    }
-
-    /// Copy a `w`×`h` tile of native pixels (row-major, little-endian bytes) into this
-    /// layer at (`x`, `y`). The tile rides inline in the request, so `w*h*4` must fit
-    /// `display_protocol.maximum_payload`.
-    pub fn blitTile(self: Layer, x: i32, y: i32, w: u32, h: u32, pixels: []const u8) bool {
-        var request = display_protocol.Request{
-            .operation = @intFromEnum(display_protocol.Operation.blit_tile),
-            .layer = self.id,
-            .x = @bitCast(x),
-            .y = @bitCast(y),
-            .width = w,
-            .height = h,
-        };
-        const header = std.mem.asBytes(&request);
-        if (header.len + pixels.len > display_protocol.message_maximum) return false;
-        var buffer: [display_protocol.message_maximum]u8 = undefined;
-        @memcpy(buffer[0..header.len], header);
-        @memcpy(buffer[header.len..][0..pixels.len], pixels);
-        const h_svc = service() orelse return false;
-        var reply: [display_protocol.reply_size]u8 = undefined;
-        const len = ipc.call(h_svc, buffer[0 .. header.len + pixels.len], &reply) catch return false;
-        if (len < display_protocol.reply_size) return false;
-        return std.mem.bytesToValue(display_protocol.Reply, reply[0..display_protocol.reply_size]).status == 0;
-    }
-
-    /// Move / restack / show or hide the layer.
-    pub fn configure(self: Layer, x: i32, y: i32, z: u32, visible: bool) bool {
-        var reply: display_protocol.Reply = undefined;
-        return transact(.{
-            .operation = @intFromEnum(display_protocol.Operation.configure_layer),
-            .layer = self.id,
-            .x = @bitCast(x),
-            .y = @bitCast(y),
-            .z = z,
-            .visible = if (visible) 1 else 0,
-        }, &reply);
-    }
-
-    /// Mark a rectangle of this layer (layer-local) dirty for the next present — for when
-    /// the layer's pixels changed without a drawing call the compositor already tracked.
-    pub fn damage(self: Layer, x: i32, y: i32, w: u32, h: u32) bool {
-        var reply: display_protocol.Reply = undefined;
-        return transact(.{
-            .operation = @intFromEnum(display_protocol.Operation.damage),
-            .layer = self.id,
-            .x = @bitCast(x),
-            .y = @bitCast(y),
-            .width = w,
-            .height = h,
-        }, &reply);
-    }
-
-    /// Release the layer and its surface.
-    pub fn destroy(self: Layer) bool {
-        var reply: display_protocol.Reply = undefined;
-        return transact(.{ .operation = @intFromEnum(display_protocol.Operation.destroy_layer), .layer = self.id }, &reply);
-    }
-};
-
-/// Create a server-owned layer of `w`×`h` pixels at screen (`x`, `y`) with stacking order
-/// `z` (higher is nearer the front), initially visible. Returns a handle, or null.
-pub fn createLayer(x: i32, y: i32, w: u32, h: u32, z: u32) ?Layer {
-    var reply: display_protocol.Reply = undefined;
-    if (!transact(.{
-        .operation = @intFromEnum(display_protocol.Operation.create_layer),
-        .x = @bitCast(x),
-        .y = @bitCast(y),
-        .width = w,
-        .height = h,
-        .z = z,
-        .visible = 1,
-    }, &reply)) return null;
-    return .{ .id = reply.layer };
-}

library/client/input/input-client.zig

@@ -21,12 +21,14 @@
 //!         if (event.asKeyboard()) |k| { ... } else if (event.asMouse()) |m| { ... }
 //!     }
 
-const std = @import("std");
+const channel = @import("channel");
-const abi = @import("abi");
+const envelope = @import("envelope");
 const ipc = @import("ipc");
 const time = @import("time");
 const input_protocol = @import("input-protocol");
 
+const Protocol = input_protocol.Protocol;
+
 pub const DeviceKind = input_protocol.DeviceKind;
 pub const InputEvent = input_protocol.InputEvent;
 pub const KeyEvent = input_protocol.KeyEvent;
@@ -44,13 +46,13 @@ pub const device_mouse = input_protocol.device_mouse;
 pub const device_joystick = input_protocol.device_joystick;
 pub const device_all = input_protocol.device_all;
 
-/// Look up the input service, retrying while it is still coming up. Both a subscriber and
+/// Open `/protocol/input`, retrying while it is still coming up. Both a subscriber and
-/// a source race the service's registration at boot, so both wait for it here rather than
+/// a source race the service's bind at boot, so both wait for it here rather than
-/// failing. Returns the service endpoint handle, or null if it never appears.
+/// failing. Returns the provider's endpoint handle, or null if it never appears.
 fn lookupService() ?ipc.Handle {
     var attempts: usize = 0;
     while (attempts < 100) : (attempts += 1) {
-        if (ipc.lookup(.input)) |handle| return handle;
+        if (channel.openEndpoint("input")) |handle| return handle;
         time.sleepMillis(50);
     }
     return null;
@@ -66,31 +68,44 @@ pub const Subscriber = struct {
     /// The endpoint the service delivers events to (created and owned by us; its handle
     /// was handed to the service as a capability at subscribe time).
     endpoint: ipc.Handle,
-    receive: [input_protocol.event_size]u8 = undefined,
+    /// A pushed packet is the folded header plus one typed event, so the buffer is
+    /// the push floor rather than any one event's size.
+    receive: [envelope.post_maximum]u8 = undefined,
 
     /// Block until the next event is pushed, and return it. Events arrive as asynchronous
     /// buffered messages (`ipc_send` from the service), so nothing is owed in reply — the
     /// empty reply this issues is a harmless no-op. Returns null for any non-event wake-up
     /// (there should be none), so callers can loop.
+    ///
+    /// The device class is the packet's operation, so it is read from the header and
+    /// re-tagged into an `InputEvent` here — one decoded type for a caller that took
+    /// several classes on one stream.
     pub fn next(self: *Subscriber) ?InputEvent {
         const got = ipc.replyWait(self.endpoint, &.{}, &self.receive, null);
-        if (!got.isMessage() or got.len < input_protocol.event_size) return null;
+        if (!got.isMessage()) return null;
-        return std.mem.bytesToValue(InputEvent, self.receive[0..input_protocol.event_size]);
+        const packet = self.receive[0..@min(got.len, self.receive.len)];
+        return switch (Protocol.eventOf(packet) orelse return null) {
+            .keyboard => InputEvent.fromKeyboard(Protocol.decodeEvent(.keyboard, packet) orelse return null),
+            .mouse => InputEvent.fromMouse(Protocol.decodeEvent(.mouse, packet) orelse return null),
+            .joystick => InputEvent.fromJoystick(Protocol.decodeEvent(.joystick, packet) orelse return null),
+        };
     }
 };
 
 /// Subscribe to the input classes named in `device_mask` (an OR of `device_*`, or
 /// `device_all`). Creates an endpoint for the service to push to and hands it over as a
-/// capability. Returns a `Subscriber` to loop `next` on, or null on failure.
+/// capability — the envelope's reserved `subscribe`, whose shape this is exactly. Returns
+/// a `Subscriber` to loop `next` on, or null on failure.
 pub fn subscribe(device_mask: u32) ?Subscriber {
     const service = lookupService() orelse return null;
     const endpoint = ipc.createIpcEndpoint() orelse return null;
 
-    var request = input_protocol.Request{ .operation = @intFromEnum(input_protocol.Operation.subscribe), .device_mask = device_mask };
+    var packet: [input_protocol.message_maximum]u8 = undefined;
-    var reply: [input_protocol.reply_size]u8 = undefined;
+    const framed = input_protocol.encodeSubscribe(device_mask, &packet) orelse return null;
-    const result = ipc.callCap(service, std.mem.asBytes(&request), &reply, endpoint) catch return null;
+    var reply: [input_protocol.message_maximum]u8 = undefined;
-    if (result.len < input_protocol.reply_size) return null;
+    const result = ipc.callCap(service, framed, &reply, endpoint) catch return null;
-    if (std.mem.bytesToValue(input_protocol.Reply, reply[0..input_protocol.reply_size]).status != 0) return null;
+    const status = envelope.statusOf(reply[0..result.len]) orelse return null;
+    if (status.status != 0) return null;
     return .{ .endpoint = endpoint };
 }
 
@@ -149,11 +164,12 @@ pub const Publisher = struct {
     service: ipc.Handle,
 
     fn publish(self: Publisher, event: InputEvent) bool {
-        var request = input_protocol.Request{ .operation = @intFromEnum(input_protocol.Operation.publish), .event = event };
+        var packet: [input_protocol.message_maximum]u8 = undefined;
-        var reply: [input_protocol.reply_size]u8 = undefined;
+        const framed = Protocol.encodeRequest(.publish, 0, event, &.{}, &packet) orelse return false;
-        const len = ipc.call(self.service, std.mem.asBytes(&request), &reply) catch return false;
+        var reply: [input_protocol.message_maximum]u8 = undefined;
-        if (len < input_protocol.reply_size) return false;
+        const len = ipc.call(self.service, framed, &reply) catch return false;
-        return std.mem.bytesToValue(input_protocol.Reply, reply[0..input_protocol.reply_size]).status == 0;
+        const status = envelope.statusOf(reply[0..len]) orelse return false;
+        return status.status == 0;
     }
 
     /// Broadcast a keyboard event to every subscriber that took keyboard events.

library/csv/build.zig

@@ -0,0 +1,20 @@
+//! The "csv" library domain: shared CSV helpers (comment stripping, field
+//! iteration) for the /system/configuration/*.csv config files — the device registry and the
+//! init service list both parse them.
+
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    _ = b.addModule("csv", .{ .root_source_file = b.path("csv.zig") });
+
+    // Standalone `zig build test` for this domain alone; the root build keeps
+    // its aggregate test step.
+    const test_step = b.step("test", "Run the csv unit tests");
+    const csv_tests = b.addTest(.{
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("csv.zig"),
+            .target = b.resolveTargetQuery(.{}),
+        }),
+    });
+    test_step.dependOn(&b.addRunArtifact(csv_tests).step);
+}

library/csv/build.zig.zon

@@ -0,0 +1,8 @@
+.{
+    .name = .csv,
+    .version = "0.0.0",
+    .fingerprint = 0x8a4525791f4e5b6, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{},
+    .paths = .{""},
+}

library/csv/csv.zig

@@ -1,5 +1,5 @@
-//! Minimal CSV helpers shared by the `/etc/*.csv` config files — the device
+//! Minimal CSV helpers shared by the `/system/configuration/*.csv` config files — the device
-//! registry (`/etc/devices.csv`) and the init service list (`/etc/init.csv`).
+//! registry (`/system/configuration/devices.csv`) and the init service list (`/system/configuration/init.csv`).
 //! Freestanding, no allocator: returned fields are slices into the source line,
 //! so the source must outlive them. `#` starts a comment (whole-line or trailing);
 //! whitespace around a field is trimmed, so columns may be padded for alignment.

library/device/block/block.zig

@@ -7,11 +7,14 @@
 //! `runtime.dma.alloc`), so whole sectors move without crossing the IPC size
 //! limit — the same handoff usb-storage uses toward the controller.
 
-const std = @import("std");
+const channel = @import("channel");
+const envelope = @import("envelope");
 const ipc = @import("ipc");
 const time = @import("time");
 const block_protocol = @import("block-protocol");
 
+const Protocol = block_protocol.Protocol;
+
 pub const Geometry = struct { block_size: u32, block_count: u64 };
 
 pub const Device = struct {
@@ -19,49 +22,67 @@ pub const Device = struct {
 
     /// The device's block size and total block count.
     pub fn geometry(self: Device) ?Geometry {
-        var request = block_protocol.Request{ .operation = @intFromEnum(block_protocol.Operation.geometry), .lba = 0, .count = 0, .physical = 0 };
+        var reply: [block_protocol.message_maximum]u8 = undefined;
-        var reply: [block_protocol.reply_size]u8 = undefined;
+        const answered = self.call(.geometry, {}, null, &reply) orelse return null;
-        const n = ipc.call(self.endpoint, std.mem.asBytes(&request), &reply) catch return null;
+        const result = Protocol.decodeReply(.geometry, answered) orelse return null;
-        if (n < block_protocol.reply_size) return null;
-        const result = std.mem.bytesToValue(block_protocol.Reply, reply[0..block_protocol.reply_size]);
-        if (result.status != 0) return null;
         return .{ .block_size = result.block_size, .block_count = result.block_count };
     }
 
+    /// Hand the block server a DMA-region capability (`handle` — from a `shareable`
+    /// dma_alloc) so it forwards it to the controller and the buffer's physical
+    /// addresses become reachable by the device. Call once per buffer before naming it
+    /// in `read`/`write`. Harmless success when no IOMMU is enforcing.
+    pub fn attach(self: Device, handle: ipc.Handle) bool {
+        var reply: [block_protocol.message_maximum]u8 = undefined;
+        return self.call(.attach, {}, handle, &reply) != null;
+    }
+
     /// Read `count` blocks starting at `lba` into the DMA buffer at `physical`.
     pub fn read(self: Device, lba: u64, count: u32, physical: u64) bool {
-        return self.transfer(.read, lba, count, physical);
+        var reply: [block_protocol.message_maximum]u8 = undefined;
+        return self.call(.read, .{ .lba = lba, .count = count, .physical = physical }, null, &reply) != null;
     }
 
     /// Write `count` blocks starting at `lba` from the DMA buffer at `physical`.
     pub fn write(self: Device, lba: u64, count: u32, physical: u64) bool {
-        return self.transfer(.write, lba, count, physical);
+        var reply: [block_protocol.message_maximum]u8 = undefined;
+        return self.call(.write, .{ .lba = lba, .count = count, .physical = physical }, null, &reply) != null;
     }
 
     /// Commit any device write cache to stable media (SCSI SYNCHRONIZE CACHE), so
     /// prior writes survive a power-off. A filesystem calls this before the machine
     /// goes down; no data transfer, so the buffer arguments are unused.
     pub fn flush(self: Device) bool {
-        return self.transfer(.flush, 0, 0, 0);
+        var reply: [block_protocol.message_maximum]u8 = undefined;
+        return self.call(.flush, {}, null, &reply) != null;
     }
 
-    fn transfer(self: Device, operation: block_protocol.Operation, lba: u64, count: u32, physical: u64) bool {
+    /// One request at the driver. `target` is always 0: one endpoint per device, so
-        var request = block_protocol.Request{ .operation = @intFromEnum(operation), .lba = lba, .count = count, .physical = physical };
+    /// there is no object within the peer to address.
-        var reply: [block_protocol.reply_size]u8 = undefined;
+    fn call(
-        const n = ipc.call(self.endpoint, std.mem.asBytes(&request), &reply) catch return false;
+        self: Device,
-        if (n < block_protocol.reply_size) return false;
+        comptime operation: Protocol.Operation,
-        return std.mem.bytesToValue(block_protocol.Reply, reply[0..block_protocol.reply_size]).status == 0;
+        request: Protocol.RequestOf(operation),
+        capability: ?ipc.Handle,
+        reply: []u8,
+    ) ?[]u8 {
+        var packet: [block_protocol.message_maximum]u8 = undefined;
+        const framed = Protocol.encodeRequest(operation, 0, request, &.{}, &packet) orelse return null;
+        const answer = ipc.callCap(self.endpoint, framed, reply, capability) catch return null;
+        const status = envelope.statusOf(reply[0..answer.len]) orelse return null;
+        if (status.status != 0) return null;
+        return reply[0..answer.len];
     }
 };
 
-/// One lookup attempt, no waiting — for a server that retries on its own
+/// One open attempt, no waiting — for a server that retries on its own
 /// timer (the fat service) instead of blocking its harness in here.
 pub fn tryOpen() ?Device {
-    if (ipc.lookup(.block)) |handle| return .{ .endpoint = handle };
+    if (channel.openEndpoint("block")) |handle| return .{ .endpoint = handle };
     return null;
 }
 
-/// Look up the block device, retrying generously while the USB storage chain
+/// Open `/protocol/block`, retrying generously while the USB storage chain
 /// (controller reset, enumeration, mass-storage bring-up) comes up.
 pub fn open() ?Device {
     // Patient: the whole USB storage chain (firmware discovery, xHCI reset and
@@ -72,7 +93,7 @@ pub fn open() ?Device {
     // completed at ~24 s); a machine whose stick genuinely failed setup should
     // not sit a further minute pretending otherwise.
     while (attempts < 600) : (attempts += 1) {
-        if (ipc.lookup(.block)) |handle| return .{ .endpoint = handle };
+        if (channel.openEndpoint("block")) |handle| return .{ .endpoint = handle };
         time.sleepMillis(50);
     }
     return null;

library/device/build.zig

@@ -0,0 +1,147 @@
+//! The "device" library domain (library/device): what a driver author imports.
+//! The flat reference data (device-abi, pci-class, acpi-ids, usb-abi, usb-ids),
+//! typed MMIO access, the driver-side client libraries (driver, pci, usb,
+//! block), the AML interpreter, and the data-driven device registry.
+
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    const kernel = b.dependency("kernel", .{});
+    const protocol = b.dependency("protocol", .{});
+    const csv = b.dependency("csv", .{});
+
+    const abi = kernel.module("abi");
+    const system_call = kernel.module("system-call");
+    const ipc = kernel.module("ipc");
+    const time = kernel.module("time");
+    // A driver finds the bus it attaches to by name — `/protocol/device-manager`,
+    // `/protocol/usb-transfer`, `/protocol/block`
+    // (docs/os-development/protocol-namespace.md).
+    const channel = kernel.module("channel");
+
+    // The devices sub-project's public interface (the flat wire types),
+    // importable by user space, unlike the kernel-internal device model it
+    // also feeds (system/kernel/device-model.zig).
+    const device_abi = b.addModule("device-abi", .{
+        .root_source_file = b.path("model/device-abi.zig"),
+    });
+    // PCI class-code decoding (class/subclass/prog-IF -> names). Pure reference
+    // data, shared by kernel discovery and any user-space PCI tool.
+    const pci_class = b.addModule("pci-class", .{
+        .root_source_file = b.path("pci/pci-class.zig"),
+    });
+    // ACPI/PnP hardware-ID (_HID) names — the flat analog of pci-class.
+    _ = b.addModule("acpi-ids", .{
+        .root_source_file = b.path("acpi/acpi-ids.zig"),
+    });
+    // The AML interpreter, a build module so the ring-3 acpi service can run
+    // the same parser the kernel does (docs/discovery.md). Pure Zig, no kernel
+    // imports — one source, two builds.
+    _ = b.addModule("aml", .{
+        .root_source_file = b.path("acpi/aml/aml.zig"),
+    });
+    // The USB device-framework wire ABI (chapter-9 set-up packets, standard +
+    // class requests, descriptors) and the USB class-code taxonomy.
+    const usb_abi = b.addModule("usb-abi", .{
+        .root_source_file = b.path("usb/usb-abi.zig"),
+    });
+    const usb_ids = b.addModule("usb-ids", .{
+        .root_source_file = b.path("usb/usb-ids.zig"),
+    });
+    // Typed volatile MMIO register access + memory-ordering barriers, for
+    // drivers on top of an mmio_map grant. Depends only on `builtin`.
+    const mmio = b.addModule("mmio", .{
+        .root_source_file = b.path("mmio/mmio.zig"),
+    });
+    // The driver author's interface: device access + the device-manager hello
+    // handshake, folded together.
+    const driver = b.addModule("driver", .{
+        .root_source_file = b.path("driver/driver.zig"),
+        .imports = &.{
+            .{ .name = "abi", .module = abi },
+            .{ .name = "channel", .module = channel },
+            .{ .name = "device-abi", .module = device_abi },
+            .{ .name = "envelope", .module = protocol.module("envelope") },
+            .{ .name = "system-call", .module = system_call },
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "time", .module = time },
+            .{ .name = "device-manager-protocol", .module = protocol.module("device-manager-protocol") },
+        },
+    });
+    // A device driver's view of its claimed PCI function: config-space header
+    // fields, BAR decode + map, capability walks (legacy + extended), MSI/MSI-X
+    // programming, power state, and function-level reset — the generic PCI
+    // mechanics every leaf PCI driver used to re-derive inline.
+    _ = b.addModule("pci", .{
+        .root_source_file = b.path("pci/pci.zig"),
+        .imports = &.{
+            .{ .name = "driver", .module = driver },
+            .{ .name = "mmio", .module = mmio },
+            .{ .name = "pci-class", .module = pci_class },
+            .{ .name = "time", .module = time },
+        },
+    });
+    // The USB class-driver transfer client: open a device on the xHCI bus and
+    // drive it (control / interrupt / bulk). Re-exports usb-abi / usb-ids as
+    // usb.abi / usb.ids for a single USB import.
+    _ = b.addModule("usb", .{
+        .root_source_file = b.path("usb/usb.zig"),
+        .imports = &.{
+            .{ .name = "channel", .module = channel },
+            .{ .name = "envelope", .module = protocol.module("envelope") },
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "time", .module = time },
+            .{ .name = "usb-transfer-protocol", .module = protocol.module("usb-transfer-protocol") },
+            .{ .name = "usb-abi", .module = usb_abi },
+            .{ .name = "usb-ids", .module = usb_ids },
+        },
+    });
+    // The block-device client — a device type, so it lives here.
+    _ = b.addModule("block", .{
+        .root_source_file = b.path("block/block.zig"),
+        .imports = &.{
+            .{ .name = "channel", .module = channel },
+            .{ .name = "envelope", .module = protocol.module("envelope") },
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "time", .module = time },
+            .{ .name = "block-protocol", .module = protocol.module("block-protocol") },
+        },
+    });
+    // The device registry: parse /system/configuration/devices.csv into match rules and bind a
+    // reported device to a driver. Pure logic (no hardware, no syscalls), so it
+    // unit-tests on the host; the device manager imports it.
+    _ = b.addModule("device-registry", .{
+        .root_source_file = b.path("registry/device-registry.zig"),
+        .imports = &.{.{ .name = "csv", .module = csv.module("csv") }},
+    });
+
+    // Standalone `zig build test` for this domain alone; the root build keeps
+    // its aggregate test step.
+    const test_step = b.step("test", "Run the device library unit tests");
+    for ([_][]const u8{
+        "model/device-abi.zig", // wire-type sizes
+        "pci/pci-class.zig", // class/subclass/prog-IF name decoding
+        "acpi/acpi-ids.zig", // _HID name decoding
+        "acpi/aml/aml.zig", // AML parse + interpret, incl. Notify dispatch
+        "usb/usb-abi.zig", // wire sizes + bit packings + set-up packet encodings
+        "usb/usb-ids.zig", // class/subclass/protocol code assignments
+        "mmio/mmio.zig", // barriers assemble + registers round-trip
+    }) |root| {
+        const device_tests = b.addTest(.{
+            .root_module = b.createModule(.{
+                .root_source_file = b.path(root),
+                .target = b.resolveTargetQuery(.{}),
+            }),
+        });
+        test_step.dependOn(&b.addRunArtifact(device_tests).step);
+    }
+    // The registry needs its csv import wired, so it doesn't fit the loop.
+    const registry_tests = b.addTest(.{
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("registry/device-registry.zig"),
+            .target = b.resolveTargetQuery(.{}),
+            .imports = &.{.{ .name = "csv", .module = csv.module("csv") }},
+        }),
+    });
+    test_step.dependOn(&b.addRunArtifact(registry_tests).step);
+}

library/device/build.zig.zon

@@ -0,0 +1,15 @@
+.{
+    .name = .device,
+    .version = "0.0.0",
+    .fingerprint = 0x92fb68eace23a4f, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{
+        // driver/block/usb/pci build on the kernel library's concern modules.
+        .kernel = .{ .path = "../kernel" },
+        // driver speaks device-manager-protocol; block/usb their transfer protocols.
+        .protocol = .{ .path = "../protocol" },
+        // device-registry parses /system/configuration/devices.csv with the shared csv helpers.
+        .csv = .{ .path = "../csv" },
+    },
+    .paths = .{""},
+}

library/device/driver/driver.zig

@@ -7,6 +7,8 @@ const std = @import("std");
 const abi = @import("abi");
 const device_abi = @import("device-abi");
 const sc = @import("system-call");
+const channel = @import("channel");
+const envelope = @import("envelope");
 const ipc = @import("ipc");
 const time = @import("time");
 const device_manager_protocol = @import("device-manager-protocol");
@@ -99,6 +101,27 @@ pub fn msiBind(device_id: u64, endpoint: usize) ?Msi {
     return .{ .address = rax, .data = @intCast(rdx) };
 }
 
+/// Map a delegated DMA-region (or shared-memory) capability into a claimed device's
+/// IOMMU domain, so the device may DMA to that buffer. The caller must own `device_id`
+/// and hold `handle` (received over IPC or from its own `dma.alloc(.. | shareable)`).
+/// Idempotent. Returns true on success (and trivially when no IOMMU is present).
+pub fn dmaBind(device_id: u64, handle: usize) bool {
+    return !failed(sc.systemCall2(.dma_bind, device_id, handle));
+}
+
+/// Unmap a previously `dmaBind`'d buffer from the device's domain.
+pub fn dmaUnbind(device_id: u64, handle: usize) bool {
+    return !failed(sc.systemCall2(.dma_unbind, device_id, handle));
+}
+
+/// Drain and log any pending IOMMU translation faults, returning the count seen. A
+/// diagnostic: a driver that suspects its device attempted an out-of-domain DMA (or a
+/// test proving enforcement) forces the hardware's fault records to the log now. Returns
+/// 0 when no IOMMU is present.
+pub fn iommuFaultDrain() usize {
+    return sc.systemCall0(.iommu_fault_drain);
+}
+
 /// Read `width` bytes (1, 2, or 4) from a port in a claimed device's `io_port`
 /// resource, at byte `offset` within it. Ring 3 has no direct `in`/`out`, so a legacy
 /// driver (PS/2, 16550 UART) reaches its ports through this claim-gated call — each
@@ -146,25 +169,38 @@ const lookup_pause_ms: u64 = 20;
 /// (best-effort standalone bring-up) or it refused the handshake. Bus drivers keep the handle
 /// to report children through; a driver that runs fine unsupervised discards it with `_ =`,
 /// and one that requires supervision bails on null. Logs the outcome itself.
+///
+/// The device this driver was assigned is the packet's `Header.target` — the manager's
+/// object addressing, so `no_device` here is a driver that serves none.
 pub fn hello(role: Role, device_id: u64) ?ipc.Handle {
     var attempts: u32 = 0;
     const manager = while (attempts < lookup_attempts) : (attempts += 1) {
-        if (ipc.lookup(.device_manager)) |handle| break handle;
+        if (channel.openEndpoint("device-manager")) |handle| break handle;
         time.sleepMillis(lookup_pause_ms);
     } else {
         std.log.info("no device manager to hello", .{});
         return null;
     };
 
-    const message = device_manager_protocol.Hello{ .role = @intFromEnum(role), .device_id = device_id };
+    var packet: [device_manager_protocol.message_maximum]u8 = undefined;
-    var reply: [device_manager_protocol.reply_size]u8 = undefined;
+    const framed = device_manager_protocol.Protocol.encodeRequest(
-    const length = ipc.call(manager, std.mem.asBytes(&message), &reply) catch {
+        .hello,
+        device_id,
+        .{ .role = @intFromEnum(role) },
+        &.{},
+        &packet,
+    ) orelse return null;
+
+    var reply: [device_manager_protocol.message_maximum]u8 = undefined;
+    const length = ipc.call(manager, framed, &reply) catch {
         std.log.info("hello call failed", .{});
         return null;
     };
-    if (length < device_manager_protocol.reply_size or
+    const status = envelope.statusOf(reply[0..length]) orelse {
-        std.mem.bytesToValue(device_manager_protocol.HelloReply, reply[0..device_manager_protocol.reply_size]).status != 0)
+        std.log.info("hello answered nothing readable", .{});
-    {
+        return null;
+    };
+    if (status.status != 0) {
         std.log.info("hello refused", .{});
         return null;
     }

library/device/model/device-abi.zig

@@ -126,7 +126,7 @@ pub const DeviceDescriptor = extern struct {
     // names with the pci-class module.
     pci_class: u64,
     // Numeric identity beyond the class triple, mirrored in the bus report's
-    // ChildAdded so /etc/devices.csv can bind on it: `vendor`/`device` are the PCI
+    // ChildAdded so /system/configuration/devices.csv can bind on it: `vendor`/`device` are the PCI
     // vendor/device (or USB idVendor/idProduct), `subsystem` is the PCI subsystem id
     // packed `(subsystem_vendor << 16) | subsystem_device`. Zero where the bus has no
     // such concept. Defaulted so existing descriptor literals keep compiling and lay

library/device/pci/pci-class.zig

@@ -52,16 +52,134 @@ pub const config_vendor_id: usize = 0x00;
 pub const config_device_id: usize = 0x02;
 pub const config_command: usize = 0x04;
 pub const config_status: usize = 0x06;
-pub const config_capabilities_pointer: usize = 0x34;
+pub const config_revision_id: usize = 0x08;
+pub const config_class_code: usize = 0x09; // 3 bytes: prog-IF 0x09, subclass 0x0A, base class 0x0B
 pub const config_bar0: usize = 0x10; // BAR0; BAR n is at config_bar0 + n*4
+pub const config_subsystem_vendor_id: usize = 0x2C;
+pub const config_subsystem_id: usize = 0x2E;
+pub const config_expansion_rom: usize = 0x30;
+pub const config_capabilities_pointer: usize = 0x34;
+pub const config_interrupt_line: usize = 0x3C;
+pub const config_interrupt_pin: usize = 0x3D; // 0 = none, 1..4 = INTA..INTD
 
-/// Command register: Memory-Space enable (bit 1) | Bus-Master enable (bit 2).
+/// Command register bits.
-pub const command_memory_and_bus_master: u16 = 0x06;
+pub const command_io_space: u16 = 0x0001; // bit 0: I/O-space decode enable
+pub const command_memory_space: u16 = 0x0002; // bit 1: memory-space decode enable
+pub const command_bus_master: u16 = 0x0004; // bit 2: bus-master (DMA) enable
+pub const command_interrupt_disable: u16 = 0x0400; // bit 10: suppress legacy INTx (MSI/MSI-X unaffected)
+/// The pair a bus-mastering driver enables together: decode my BARs, let me DMA.
+pub const command_memory_and_bus_master: u16 = command_memory_space | command_bus_master;
+
+/// Status register bit 3: legacy INTx is asserted (upstream of the command bit-10 gate).
+pub const status_interrupt: u16 = 0x0008;
 /// Status register bit 4: a capability list is present at config_capabilities_pointer.
 pub const status_capabilities_list: u16 = 0x10;
 /// Capability pointers are dword-aligned; the low two bits are reserved.
 pub const capability_pointer_mask: u8 = 0xFC;
 
+/// Capability IDs — the first byte of each entry in the legacy capability list.
+/// Non-exhaustive: hardware may report IDs not named here.
+pub const CapabilityId = enum(u8) {
+    power_management = 0x01,
+    msi = 0x05,
+    vendor_specific = 0x09,
+    pci_express = 0x10,
+    msix = 0x11,
+    _,
+};
+
+/// MSI capability (id 0x05) register layout. Offsets are relative to the capability
+/// header; whether the address is one or two dwords (and therefore where the data word
+/// sits) depends on `control_64bit_capable`.
+pub const msi = struct {
+    pub const control: usize = 0x02; // u16 Message Control
+    pub const control_enable: u16 = 0x0001;
+    pub const control_multiple_message_capable_mask: u16 = 0x000E; // bits 3:1, log2(vectors requested)
+    pub const control_multiple_message_enable_mask: u16 = 0x0070; // bits 6:4, log2(vectors granted)
+    pub const control_64bit_capable: u16 = 0x0080; // bit 7: address is 64-bit (layout shifts)
+    pub const control_per_vector_masking: u16 = 0x0100; // bit 8
+    pub const address: usize = 0x04; // u32 low address dword (both layouts)
+    pub const address_high: usize = 0x08; // u32, present only when 64-bit capable
+    pub const data_32: usize = 0x08; // u16 message data, 32-bit layout
+    pub const data_64: usize = 0x0C; // u16 message data, 64-bit layout
+    pub const mask_bits_32: usize = 0x0C; // u32, only with per-vector masking
+    pub const mask_bits_64: usize = 0x10;
+};
+
+/// MSI-X capability (id 0x11) register layout, plus the 16-byte vector table entry that
+/// lives in BAR space (not configuration space) at the decoded (BIR, offset).
+pub const msix = struct {
+    pub const control: usize = 0x02; // u16 Message Control
+    pub const control_table_size_mask: u16 = 0x07FF; // bits 10:0, encoded as N-1
+    pub const control_function_mask: u16 = 0x4000; // bit 14: mask every vector
+    pub const control_enable: u16 = 0x8000; // bit 15
+    pub const table_offset_word: usize = 0x04; // u32: BIR in bits 2:0, table offset in bits 31:3
+    pub const pba_offset_word: usize = 0x08; // u32: same encoding, pending-bit array
+    pub const bir_mask: u32 = 0x0000_0007;
+    pub const offset_mask: u32 = 0xFFFF_FFF8;
+    pub const entry_size: usize = 16; // table entry stride; offsets within an entry:
+    pub const entry_address: usize = 0x0; // u32 low
+    pub const entry_address_high: usize = 0x4; // u32 high
+    pub const entry_data: usize = 0x8; // u32
+    pub const entry_vector_control: usize = 0xC; // u32
+    pub const entry_vector_control_masked: u32 = 0x1; // bit 0; entries reset to masked
+
+    /// Where the table (or pending-bit array) lives, decoded from its offset/BIR dword.
+    pub const TableLocation = struct { bar: u8, offset: u32 };
+    pub fn tableLocation(word: u32) TableLocation {
+        return .{ .bar = @intCast(word & bir_mask), .offset = word & offset_mask };
+    }
+    /// Number of table entries (the control field encodes N-1).
+    pub fn tableSize(control_value: u16) u16 {
+        return (control_value & control_table_size_mask) + 1;
+    }
+};
+
+/// Power-management capability (id 0x01) register layout.
+pub const power_management = struct {
+    pub const capabilities: usize = 0x02; // u16 PMC (read-only: version, D-state support)
+    pub const control_status: usize = 0x04; // u16 PMCSR
+    pub const control_status_power_state_mask: u16 = 0x0003; // bits 1:0
+    pub const power_state_d0: u16 = 0x0;
+    pub const power_state_d3_hot: u16 = 0x3;
+    pub const control_status_pme_enable: u16 = 0x0100; // bit 8: plain RW — preserve on writes
+    pub const control_status_pme_status: u16 = 0x8000; // bit 15: RW1C — write 0 or you clear it
+};
+
+/// PCI Express capability (id 0x10) register layout — the slice function-level reset
+/// needs; the full capability is much larger.
+pub const pci_express = struct {
+    pub const capabilities: usize = 0x02; // u16 PCIe Capabilities register
+    pub const device_capabilities: usize = 0x04; // u32
+    pub const device_capabilities_flr: u32 = 1 << 28; // Function Level Reset supported
+    pub const device_control: usize = 0x08; // u16
+    pub const device_control_initiate_flr: u16 = 1 << 15;
+    pub const device_status: usize = 0x0A; // u16
+    pub const device_status_transactions_pending: u16 = 1 << 5;
+};
+
+/// Extended (PCI Express) capabilities start here in the 4 KiB configuration space; a
+/// conventional-PCI function has nothing there (the space reads as all-ones).
+pub const extended_capability_start: usize = 0x100;
+/// Extended-capability next pointers are dword-aligned within the 4 KiB space.
+pub const extended_capability_pointer_mask: u16 = 0xFFC;
+
+/// The 32-bit header at the start of each extended capability: ID in bits 15:0,
+/// version in 19:16, next offset in 31:20 (0 = end of list).
+pub const ExtendedCapabilityHeader = struct {
+    id: u16,
+    version: u4,
+    next: u16,
+
+    pub fn decode(word: u32) ExtendedCapabilityHeader {
+        return .{
+            .id = @truncate(word),
+            .version = @truncate(word >> 16),
+            .next = @intCast((word >> 20) & extended_capability_pointer_mask),
+        };
+    }
+};
+
 /// BAR bit layout: bit 0 selects I/O (1) vs memory (0) space; for a memory BAR, bits 2:1
 /// give the type (00 = 32-bit, 10 = 64-bit spanning the next BAR), and the base address is
 /// the dword with the low 4 flag bits masked off.
@@ -595,3 +713,37 @@ test "named parts pack to the raw triple" {
     };
     try std.testing.expectEqual(@as(u24, 0x0C_03_30), xhci.pack());
 }
+
+test "MSI-X table word decodes to BIR and offset" {
+    const eq = std.testing.expectEqual;
+    // BIR 3, table at 0x2000 within that BAR.
+    try eq(msix.TableLocation{ .bar = 3, .offset = 0x2000 }, msix.tableLocation(0x0000_2003));
+    // BIR 0, offset 0 — the degenerate-but-common "table at BAR start" case.
+    try eq(msix.TableLocation{ .bar = 0, .offset = 0 }, msix.tableLocation(0));
+    // Table size encodes N-1 in bits 10:0; enable/function-mask bits must not leak in.
+    try eq(@as(u16, 11), msix.tableSize(msix.control_enable | 0x000A));
+    try eq(@as(u16, 1), msix.tableSize(0));
+    try eq(@as(u16, 2048), msix.tableSize(msix.control_table_size_mask));
+}
+
+test "extended capability header unpacks id, version, next" {
+    const eq = std.testing.expectEqual;
+    // AER (id 0x0001), version 1, next capability at 0x140.
+    const aer = ExtendedCapabilityHeader.decode(0x1401_0001);
+    try eq(@as(u16, 0x0001), aer.id);
+    try eq(@as(u4, 1), aer.version);
+    try eq(@as(u16, 0x140), aer.next);
+    // A zero header is the "nothing here" terminator.
+    const none = ExtendedCapabilityHeader.decode(0);
+    try eq(@as(u16, 0), none.id);
+    try eq(@as(u16, 0), none.next);
+}
+
+test "command bits and capability ids compose" {
+    const eq = std.testing.expectEqual;
+    try eq(command_memory_space | command_bus_master, command_memory_and_bus_master);
+    try eq(@as(u8, 0x05), @intFromEnum(CapabilityId.msi));
+    try eq(@as(u8, 0x11), @intFromEnum(CapabilityId.msix));
+    try eq(@as(u8, 0x01), @intFromEnum(CapabilityId.power_management));
+    try eq(@as(u8, 0x10), @intFromEnum(CapabilityId.pci_express));
+}

library/device/pci/pci.zig

@@ -1,7 +1,8 @@
 //! library/device/pci/pci.zig — a device driver's view of the ONE PCI function it has
-//! claimed. Config space is mapped as resource 0; this gives header-field accessors, BAR
+//! claimed. Config space is mapped as resource 0 (a full 4 KiB ECAM page); this gives
-//! decode + map, and a capability-list iterator, so a driver never re-derives the
+//! header-field accessors, BAR decode + map, capability walks (legacy and extended),
-//! config-space layout by hand.
+//! MSI/MSI-X programming, power-state handling, and function-level reset, so a driver
+//! never re-derives the config-space layout by hand.
 //!
 //! This is the *device-owned* view: read my own function's live config, map my own BARs.
 //! The bus enumerator's view — probing arbitrary, not-yet-claimed functions and sizing
@@ -13,6 +14,18 @@ const std = @import("std");
 const mmio = @import("mmio");
 const pci_class = @import("pci-class");
 const device = @import("driver");
+const time = @import("time");
+
+/// Spec recovery time after a D3hot -> D0 transition.
+const d0_recovery_millis: u64 = 10;
+/// How long to wait for in-flight transactions to drain before a function-level reset
+/// (then reset anyway — resetting a stuck function is the point of FLR).
+const flr_pending_timeout_millis: u64 = 100;
+/// The spec's maximum FLR completion time.
+const flr_settle_millis: u64 = 100;
+/// How long to wait for the function to become readable again after an FLR.
+const flr_ready_timeout_millis: u64 = 1000;
+const flr_poll_interval_millis: u64 = 10;
 
 /// A claimed PCI function whose configuration space is mapped (resource 0). `descriptor`
 /// must outlive the Function — the driver's `device.enumerate` buffer does, for the whole
@@ -42,12 +55,61 @@ pub const Function = struct {
     pub fn status(self: *const Function) u16 {
         return mmio.readRegister(u16, self.config + pci_class.config_status);
     }
+    pub fn revisionId(self: *const Function) u8 {
+        return mmio.readRegister(u8, self.config + pci_class.config_revision_id);
+    }
+    /// Subsystem vendor ID (config 0x2C) — with `subsystemId`, the standard key for
+    /// board-level quirk matching.
+    pub fn subsystemVendorId(self: *const Function) u16 {
+        return mmio.readRegister(u16, self.config + pci_class.config_subsystem_vendor_id);
+    }
+    pub fn subsystemId(self: *const Function) u16 {
+        return mmio.readRegister(u16, self.config + pci_class.config_subsystem_id);
+    }
+    /// Interrupt pin (config 0x3D): 0 = none, 1..4 = INTA..INTD.
+    pub fn interruptPin(self: *const Function) u8 {
+        return mmio.readRegister(u8, self.config + pci_class.config_interrupt_pin);
+    }
+    /// The live class-code triple (config 0x09..0x0B), same shape discovery records.
+    pub fn classCode(self: *const Function) pci_class.ClassCode {
+        return .{
+            .prog_if = mmio.readRegister(u8, self.config + pci_class.config_class_code),
+            .subclass = mmio.readRegister(u8, self.config + pci_class.config_class_code + 1),
+            .base = mmio.readRegister(u8, self.config + pci_class.config_class_code + 2),
+        };
+    }
 
-    /// Set Memory-Space + Bus-Master enable in the command register. Firmware often leaves
+    fn commandSetBits(self: *const Function, bits: u16) void {
-    /// a secondary display's decode off; a bus-mastering device must enable both.
-    pub fn enableMemoryAndBusMaster(self: *const Function) void {
         const at = self.config + pci_class.config_command;
-        mmio.writeRegister(u16, at, mmio.readRegister(u16, at) | pci_class.command_memory_and_bus_master);
+        mmio.writeRegister(u16, at, mmio.readRegister(u16, at) | bits);
+    }
+    fn commandClearBits(self: *const Function, bits: u16) void {
+        const at = self.config + pci_class.config_command;
+        mmio.writeRegister(u16, at, mmio.readRegister(u16, at) & ~bits);
+    }
+
+    /// Set Memory-Space + Bus-Master Enable in the command register. Firmware only enables
+    /// memory decode on devices it used at boot; any other device has dead BARs until its
+    /// driver sets it. Bus mastering is separately required for the device to do DMA.
+    pub fn enableMemoryAndBusMaster(self: *const Function) void {
+        self.commandSetBits(pci_class.command_memory_and_bus_master);
+    }
+
+    /// Clear Bus-Master Enable — stop the device initiating DMA. The quiesce half of a
+    /// driver's shutdown (or a supervisor restart): after this the device can no longer
+    /// write memory the process is about to stop owning.
+    pub fn disableBusMaster(self: *const Function) void {
+        self.commandClearBits(pci_class.command_bus_master);
+    }
+
+    /// Set command bit 10: suppress legacy INTx assertion. MSI/MSI-X are unaffected —
+    /// set this when enabling either, so the device cannot also raise the shared pin.
+    pub fn setInterruptDisable(self: *const Function) void {
+        self.commandSetBits(pci_class.command_interrupt_disable);
+    }
+    /// Clear command bit 10, re-allowing legacy INTx assertion.
+    pub fn clearInterruptDisable(self: *const Function) void {
+        self.commandClearBits(pci_class.command_interrupt_disable);
     }
 
     /// Decode BAR `bar` (0..5) and map it: read the BAR register, reject I/O-space BARs,
@@ -86,6 +148,129 @@ pub const Function = struct {
             0;
         return .{ .config = self.config, .cursor = first };
     }
+
+    /// First capability with `id`, or null.
+    pub fn findCapability(self: *const Function, id: pci_class.CapabilityId) ?Capability {
+        var walk = self.capabilities();
+        while (walk.next()) |capability| {
+            if (capability.id == @intFromEnum(id)) return capability;
+        }
+        return null;
+    }
+
+    /// Program the MSI capability with the kernel's `msi_bind` result and enable it —
+    /// one vector (multiple-message-enable 0, matching the kernel's single-vector
+    /// grant), INTx suppressed. false if the function has no MSI capability.
+    pub fn programMsi(self: *const Function, message: device.Msi) bool {
+        const cap = self.findCapability(.msi) orelse return false;
+        const control_at = cap.offset + pci_class.msi.control;
+        const control = mmio.readRegister(u16, control_at);
+        // Program the registers while the capability is disabled.
+        mmio.writeRegister(u16, control_at, control & ~pci_class.msi.control_enable);
+        mmio.writeRegister(u32, cap.offset + pci_class.msi.address, @truncate(message.address));
+        const data_offset = if (control & pci_class.msi.control_64bit_capable != 0) offset: {
+            mmio.writeRegister(u32, cap.offset + pci_class.msi.address_high, @intCast(message.address >> 32));
+            break :offset pci_class.msi.data_64;
+        } else pci_class.msi.data_32;
+        // Message data is a 16-bit register in both layouts.
+        mmio.writeRegister(u16, cap.offset + data_offset, @truncate(message.data));
+        mmio.writeRegister(u16, control_at, (control & ~pci_class.msi.control_multiple_message_enable_mask) | pci_class.msi.control_enable);
+        self.setInterruptDisable();
+        return true;
+    }
+
+    /// Clear the MSI enable bit. No-op if the function has no MSI capability.
+    pub fn disableMsi(self: *const Function) void {
+        const cap = self.findCapability(.msi) orelse return;
+        const control_at = cap.offset + pci_class.msi.control;
+        mmio.writeRegister(u16, control_at, mmio.readRegister(u16, control_at) & ~pci_class.msi.control_enable);
+    }
+
+    /// The function's MSI-X capability with its vector table mapped: the table's BIR is
+    /// resolved through `mapBar` (a free cache hit when it is a BAR the driver already
+    /// mapped). null if the capability is absent or the table's BAR cannot be mapped.
+    pub fn msix(self: *Function) ?MsiX {
+        const cap = self.findCapability(.msix) orelse return null;
+        const control = mmio.readRegister(u16, cap.offset + pci_class.msix.control);
+        const word = mmio.readRegister(u32, cap.offset + pci_class.msix.table_offset_word);
+        const location = pci_class.msix.tableLocation(word);
+        const bar_base = self.mapBar(location.bar) orelse return null;
+        return .{
+            .capability = cap.offset,
+            .table = bar_base + location.offset,
+            .entry_count = pci_class.msix.tableSize(control),
+        };
+    }
+
+    /// Bring the function to D0. Firmware can leave a non-boot device in D3hot, where
+    /// its BARs and MSI registers do not decode; call this before touching either. No
+    /// power-management capability means the function is always at D0: nothing to do.
+    /// Preserves PME-Enable and never clears the write-1-to-clear PME-Status bit.
+    pub fn ensurePowerStateD0(self: *const Function) void {
+        const cap = self.findCapability(.power_management) orelse return;
+        const at = cap.offset + pci_class.power_management.control_status;
+        const pmcsr = mmio.readRegister(u16, at);
+        if (pmcsr & pci_class.power_management.control_status_power_state_mask == pci_class.power_management.power_state_d0) return;
+        // PME-Status is RW1C: echoing a read 1 back would clear it, so write it as 0.
+        mmio.writeRegister(u16, at, (pmcsr & ~pci_class.power_management.control_status_power_state_mask & ~pci_class.power_management.control_status_pme_status) | pci_class.power_management.power_state_d0);
+        time.sleepMillis(d0_recovery_millis);
+    }
+
+    /// Function Level Reset via the PCI Express capability: return the hardware to a
+    /// known state (a supervisor re-claiming a device after its driver died, or a driver
+    /// recovering a wedged function). The six BAR dwords are saved and restored — FLR
+    /// clears them, and the bus enumerator's assignment must survive for the descriptor
+    /// correlation and `mapBar` cache to stay valid. Everything else is reset: command
+    /// enables and MSI/MSI-X programming are gone, so the caller re-runs its whole
+    /// bring-up afterwards. false if the function has no PCI Express capability, does
+    /// not advertise FLR (conventional-PCI Advanced Features FLR is a possible
+    /// follow-up), or never became readable again. Blocks for at least 100 ms.
+    pub fn functionLevelReset(self: *const Function) bool {
+        const cap = self.findCapability(.pci_express) orelse return false;
+        const device_capabilities = mmio.readRegister(u32, cap.offset + pci_class.pci_express.device_capabilities);
+        if (device_capabilities & pci_class.pci_express.device_capabilities_flr == 0) return false;
+
+        // Stop new DMA, then give in-flight transactions a bounded chance to drain —
+        // and reset anyway on timeout, since resetting a stuck function is the point.
+        self.disableBusMaster();
+        var waited: u64 = 0;
+        while (mmio.readRegister(u16, cap.offset + pci_class.pci_express.device_status) & pci_class.pci_express.device_status_transactions_pending != 0) {
+            if (waited >= flr_pending_timeout_millis) break;
+            time.sleepMillis(flr_poll_interval_millis);
+            waited += flr_poll_interval_millis;
+        }
+
+        var bars: [6]u32 = undefined;
+        for (&bars, 0..) |*bar, index| bar.* = mmio.readRegister(u32, self.config + pci_class.config_bar0 + index * 4);
+
+        const control_at = cap.offset + pci_class.pci_express.device_control;
+        mmio.writeRegister(u16, control_at, mmio.readRegister(u16, control_at) | pci_class.pci_express.device_control_initiate_flr);
+        time.sleepMillis(flr_settle_millis);
+
+        waited = 0;
+        while (self.vendorId() == 0xFFFF) {
+            if (waited >= flr_ready_timeout_millis) return false;
+            time.sleepMillis(flr_poll_interval_millis);
+            waited += flr_poll_interval_millis;
+        }
+        for (bars, 0..) |bar, index| mmio.writeRegister(u32, self.config + pci_class.config_bar0 + index * 4, bar);
+        return true;
+    }
+
+    /// Iterate the extended (PCI Express) capability list at 0x100.. in the 4 KiB ECAM
+    /// page. Empty on a conventional-PCI function (the space reads as all-ones).
+    pub fn extendedCapabilities(self: *const Function) ExtendedCapabilityIterator {
+        return .{ .config = self.config };
+    }
+
+    /// First extended capability with `id`, or null.
+    pub fn findExtendedCapability(self: *const Function, id: u16) ?ExtendedCapability {
+        var walk = self.extendedCapabilities();
+        while (walk.next()) |capability| {
+            if (capability.id == id) return capability;
+        }
+        return null;
+    }
 };
 
 /// One capability header. `offset` is the ABSOLUTE virtual address of the header, so the
@@ -106,3 +291,94 @@ pub const CapabilityIterator = struct {
         return .{ .id = id, .offset = at };
     }
 };
+
+/// A resolved MSI-X capability from `Function.msix`: `capability` is the absolute
+/// virtual address of the config-space header, `table` of vector-table entry 0 (in BAR
+/// space — table writes are MMIO, not config space). Entries reset masked; bring-up
+/// order is programEntry per vector, unmaskEntry per used vector, `enable`, then
+/// `Function.setInterruptDisable`.
+pub const MsiX = struct {
+    capability: usize,
+    table: usize,
+    entry_count: u16,
+
+    /// Write `message` into table entry `entry`, leaving the entry masked (its reset
+    /// state) — the spec requires masking while address/data change. false if `entry`
+    /// is out of range.
+    pub fn programEntry(self: *const MsiX, entry: u16, message: device.Msi) bool {
+        if (entry >= self.entry_count) return false;
+        const at = self.table + @as(usize, entry) * pci_class.msix.entry_size;
+        mmio.writeRegister(u32, at + pci_class.msix.entry_vector_control, pci_class.msix.entry_vector_control_masked);
+        mmio.writeRegister(u32, at + pci_class.msix.entry_address, @truncate(message.address));
+        mmio.writeRegister(u32, at + pci_class.msix.entry_address_high, @intCast(message.address >> 32));
+        mmio.writeRegister(u32, at + pci_class.msix.entry_data, message.data);
+        return true;
+    }
+
+    /// Set the entry's vector-control mask bit — its interrupt is held off (pended in
+    /// the PBA, not lost). false if `entry` is out of range.
+    pub fn maskEntry(self: *const MsiX, entry: u16) bool {
+        return self.writeEntryMask(entry, true);
+    }
+    /// Clear the entry's vector-control mask bit. false if `entry` is out of range.
+    pub fn unmaskEntry(self: *const MsiX, entry: u16) bool {
+        return self.writeEntryMask(entry, false);
+    }
+    fn writeEntryMask(self: *const MsiX, entry: u16, masked: bool) bool {
+        if (entry >= self.entry_count) return false;
+        const at = self.table + @as(usize, entry) * pci_class.msix.entry_size + pci_class.msix.entry_vector_control;
+        const control = mmio.readRegister(u32, at);
+        mmio.writeRegister(u32, at, if (masked)
+            control | pci_class.msix.entry_vector_control_masked
+        else
+            control & ~pci_class.msix.entry_vector_control_masked);
+        return true;
+    }
+
+    /// Set the function-mask control bit: every vector masked regardless of entry bits.
+    pub fn setFunctionMask(self: *const MsiX) void {
+        self.writeControl(pci_class.msix.control_function_mask, true);
+    }
+    /// Clear the function-mask control bit.
+    pub fn clearFunctionMask(self: *const MsiX) void {
+        self.writeControl(pci_class.msix.control_function_mask, false);
+    }
+    /// Set MSI-X Enable. The caller also calls `Function.setInterruptDisable` (INTx off).
+    pub fn enable(self: *const MsiX) void {
+        self.writeControl(pci_class.msix.control_enable, true);
+    }
+    /// Clear MSI-X Enable.
+    pub fn disable(self: *const MsiX) void {
+        self.writeControl(pci_class.msix.control_enable, false);
+    }
+    fn writeControl(self: *const MsiX, bit: u16, set: bool) void {
+        const at = self.capability + pci_class.msix.control;
+        const control = mmio.readRegister(u16, at);
+        mmio.writeRegister(u16, at, if (set) control | bit else control & ~bit);
+    }
+};
+
+/// One extended capability. `offset` is the ABSOLUTE virtual address of its header,
+/// like `Capability.offset`.
+pub const ExtendedCapability = struct { id: u16, version: u4, offset: usize };
+
+pub const ExtendedCapabilityIterator = struct {
+    config: usize,
+    cursor: u16 = @intCast(pci_class.extended_capability_start),
+    guard: u32 = 0, // bounds a malformed chain (480 = the 0xF00-byte space / 8-byte minimum spacing)
+
+    pub fn next(self: *ExtendedCapabilityIterator) ?ExtendedCapability {
+        if (self.cursor == 0 or self.guard >= 480) return null;
+        self.guard += 1;
+        const at = self.config + self.cursor;
+        const header = pci_class.ExtendedCapabilityHeader.decode(mmio.readRegister(u32, at));
+        // Id 0 marks an empty list; all-ones is a conventional-PCI function (no
+        // extended space — reads come back as FFs).
+        if (header.id == 0 or header.id == 0xFFFF) return null;
+        // A next pointer below 0x100 would walk into the legacy header; treat it as the
+        // terminator it must be (0 is the normal one). The 0xFFC decode mask already
+        // keeps `config + cursor + 4` inside the 4 KiB page.
+        self.cursor = if (header.next >= pci_class.extended_capability_start) header.next else 0;
+        return .{ .id = header.id, .version = header.version, .offset = at };
+    }
+};

library/device/registry/device-registry.zig

@@ -1,4 +1,4 @@
-//! The device registry: parse `/etc/devices.csv` into match rules and bind a
+//! The device registry: parse `/system/configuration/devices.csv` into match rules and bind a
 //! reported device to a driver. This is the data-driven replacement for the
 //! device manager's three hand-written `switch` tables (`pciDriverForIdentity`,
 //! `hidDriverFor`, `usbDriverForIdentity`); the registry is now **authoritative**
@@ -11,7 +11,7 @@
 //! That keeps this module freestanding and unit-testable with plain `zig test`.
 //!
 //! The file format (docs/device-driver-development/device-manager.md, and the
-//! `/etc/devices.csv` header itself): one rule per line, nine comma-separated
+//! `/system/configuration/devices.csv` header itself): one rule per line, nine comma-separated
 //! fields, `#` starts a comment (whole-line or trailing), blank lines ignored.
 //!
 //!     bus, base, class, prog_if, vendor, device, subsystem, hid, driver
@@ -226,7 +226,7 @@ fn parseLine(line: []const u8) Line {
     } };
 }
 
-/// Parse a whole `/etc/devices.csv` into `out_rules`. The string fields of the
+/// Parse a whole `/system/configuration/devices.csv` into `out_rules`. The string fields of the
 /// returned rules point into `source`, which must outlive them.
 pub fn parse(source: []const u8, out_rules: []Rule) ParseResult {
     var result: ParseResult = .{ .count = 0, .malformed = 0, .truncated = false };

library/device/usb/usb.zig

@@ -11,15 +11,24 @@
 //!     _ = device.subscribeInterrupt(address, length); // reports arrive asynchronously
 //!     while (true) { ... ipc.replyWait(device.endpoint, ...) ... }  // its own loop
 //!
-//! Reports are delivered to `device.endpoint` as asynchronous `InterruptReport`
+//! Reports are delivered to `device.endpoint` as asynchronous `interrupt_report`
-//! messages (the class driver runs a bare `replyWait` loop to read them, because
+//! event packets, decoded with `reportOf` (the class driver runs a bare `replyWait`
-//! the service harness drops buffered-message payloads — see service.zig).
+//! loop to read them, because the service harness drops buffered-message payloads
+//! — see service.zig).
+//!
+//! Every packet this file lays down is an envelope packet: the verb and the
+//! device token in the folded `Header`, the transfer's own fields after it, and
+//! a control transfer's data stage in the tail.
 
 const std = @import("std");
+const channel = @import("channel");
+const envelope = @import("envelope");
 const ipc = @import("ipc");
 const time = @import("time");
 const usb_transfer_protocol = @import("usb-transfer-protocol");
 
+const Protocol = usb_transfer_protocol.Protocol;
+
 /// The USB chapter-9 wire ABI and the class taxonomy, re-exported so a class driver reaches
 /// the whole USB domain through its one `usb` import (`usb.abi.getDescriptor`, `usb.ids.Class`).
 pub const abi = @import("usb-abi");
@@ -56,21 +65,41 @@ pub const Device = struct {
         return null;
     }
 
+    /// One request at the bus driver, addressing this device by its token — the
+    /// packet's `Header.target`, so no request body ever names the device again.
+    /// Null covers both a failed transport and a refusal: a class driver has the
+    /// same recourse either way.
+    fn call(
+        self: *Device,
+        comptime operation: Protocol.Operation,
+        request: Protocol.RequestOf(operation),
+        tail: []const u8,
+        capability: ?ipc.Handle,
+        reply: []u8,
+    ) ?[]u8 {
+        var packet: [usb_transfer_protocol.message_maximum]u8 = undefined;
+        const framed = Protocol.encodeRequest(operation, self.token, request, tail, &packet) orelse return null;
+        const answer = ipc.callCap(self.bus, framed, reply, capability) catch return null;
+        const status = envelope.statusOf(reply[0..answer.len]) orelse return null;
+        if (status.status != 0) return null;
+        return reply[0..answer.len];
+    }
+
+    /// The data stage rides the tail in both directions, so the answer's length
+    /// *is* the transferred length — `Status.len`, which the envelope stamps.
     fn controlTransfer(self: *Device, setup: [8]u8, direction_in: bool, data: []u8) ?usize {
-        var request = usb_transfer_protocol.ControlRequest{
+        if (data.len > usb_transfer_protocol.max_inline_data) return null;
-            .device_token = self.token,
+        const outgoing: []const u8 = if (direction_in) &.{} else data;
+        var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
+        const answered = self.call(.control, .{
             .setup = setup,
             .direction_in = @intFromBool(direction_in),
             .data_length = @intCast(data.len),
-        };
+        }, outgoing, null, &reply) orelse return null;
-        if (!direction_in and data.len > 0) @memcpy(request.data[0..data.len], data);
+
-        var reply: [@sizeOf(usb_transfer_protocol.ControlReply)]u8 = undefined;
+        const returned = Protocol.replyTail(.control, answered);
-        const length = ipc.call(self.bus, std.mem.asBytes(&request), &reply) catch return null;
+        const actual = @min(returned.len, data.len);
-        if (length < @sizeOf(usb_transfer_protocol.ControlReply)) return null;
+        if (direction_in and actual > 0) @memcpy(data[0..actual], returned[0..actual]);
-        const control_reply = std.mem.bytesToValue(usb_transfer_protocol.ControlReply, reply[0..@sizeOf(usb_transfer_protocol.ControlReply)]);
-        if (control_reply.status != 0) return null;
-        const actual = @min(control_reply.actual_length, data.len);
-        if (direction_in and actual > 0) @memcpy(data[0..actual], control_reply.data[0..actual]);
         return actual;
     }
 
@@ -88,52 +117,70 @@ pub const Device = struct {
     /// Begin periodic IN polling of an interrupt endpoint; reports flow back to
     /// `self.endpoint` as asynchronous `InterruptReport` messages.
     pub fn subscribeInterrupt(self: *Device, endpoint_address: u8, max_length: u16) bool {
-        var request = usb_transfer_protocol.InterruptSubscribeRequest{
+        var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
-            .device_token = self.token,
+        return self.call(.interrupt_subscribe, .{
             .endpoint_address = endpoint_address,
             .max_length = max_length,
-        };
+        }, &.{}, null, &reply) != null;
-        var reply: [@sizeOf(usb_transfer_protocol.InterruptSubscribeReply)]u8 = undefined;
+    }
-        const length = ipc.call(self.bus, std.mem.asBytes(&request), &reply) catch return false;
+
-        if (length < @sizeOf(usb_transfer_protocol.InterruptSubscribeReply)) return false;
+    /// Hand the controller a DMA-region capability (`handle` — from a `shareable`
-        return std.mem.bytesToValue(usb_transfer_protocol.InterruptSubscribeReply, reply[0..@sizeOf(usb_transfer_protocol.InterruptSubscribeReply)]).status == 0;
+    /// dma_alloc, or forwarded from another process) so it binds that buffer into its
+    /// IOMMU domain. Must be called for every buffer whose physical address this device
+    /// will name in a `bulk` transfer, before the transfer. Harmless (and a no-op
+    /// success) when no IOMMU is enforcing. Returns false on failure.
+    pub fn attachDma(self: *Device, handle: ipc.Handle) bool {
+        var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
+        return self.call(.dma_attach, {}, &.{}, handle, &reply) != null;
     }
 
     /// One bulk transfer (IN or OUT per `endpoint_address`'s direction bit) to or
     /// from the caller's own DMA buffer at `physical`. Returns the bytes moved.
     pub fn bulk(self: *Device, endpoint_address: u8, physical: u64, length: u32) ?u32 {
-        var request = usb_transfer_protocol.BulkRequest{
+        var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
-            .device_token = self.token,
+        const answered = self.call(.bulk, .{
             .physical_address = physical,
             .length = length,
             .endpoint_address = endpoint_address,
-        };
+        }, &.{}, null, &reply) orelse return null;
-        var reply: [@sizeOf(usb_transfer_protocol.BulkReply)]u8 = undefined;
+        return (Protocol.decodeReply(.bulk, answered) orelse return null).actual_length;
-        const replied = ipc.call(self.bus, std.mem.asBytes(&request), &reply) catch return null;
-        if (replied < @sizeOf(usb_transfer_protocol.BulkReply)) return null;
-        const bulk_reply = std.mem.bytesToValue(usb_transfer_protocol.BulkReply, reply[0..@sizeOf(usb_transfer_protocol.BulkReply)]);
-        if (bulk_reply.status != 0) return null;
-        return bulk_reply.actual_length;
     }
 };
 
-/// Look up the USB bus and open the device with the assigned id, handing over a
+/// Decode one asynchronous interrupt report out of a packet that arrived on the
-/// freshly created endpoint for asynchronous interrupt reports. Retries while the
+/// class driver's own endpoint. Null when it is not one — a stray message, or a
-/// bus is still coming up (a class driver races the bus driver at boot).
+/// packet too short to carry the report it names. The device it came from is the
+/// packet's `Header.target`, which a single-device class driver never has to read.
+pub fn reportOf(packet: []const u8) ?InterruptReport {
+    const event = Protocol.eventOf(packet) orelse return null;
+    if (event != .interrupt_report) return null;
+    return Protocol.decodeEvent(.interrupt_report, packet);
+}
+
+/// Open `/protocol/usb-transfer` and, on that channel, open the device with the
+/// assigned id, handing over a freshly created endpoint for asynchronous interrupt
+/// reports. Retries while the bus is still coming up (a class driver races the bus
+/// driver at boot). Two opens, deliberately: the first names the contract, the
+/// second names an object within it.
 pub fn open(device_id: u64) ?Device {
     var attempts: usize = 0;
     const bus = while (attempts < 100) : (attempts += 1) {
-        if (ipc.lookup(.usb_bus)) |handle| break handle;
+        if (channel.openEndpoint("usb-transfer")) |handle| break handle;
         time.sleepMillis(20);
     } else return null;
 
     const endpoint = ipc.createIpcEndpoint() orelse return null;
-    var request = usb_transfer_protocol.OpenRequest{ .device_id = device_id };
+    // The assigned device id is the target: it is what the caller has before a
-    var reply: [@sizeOf(usb_transfer_protocol.OpenReply)]u8 = undefined;
+    // token exists, and the token the reply hands back addresses every packet
-    const result = ipc.callCap(bus, std.mem.asBytes(&request), &reply, endpoint) catch return null;
+    // after this one.
-    if (result.len < @sizeOf(usb_transfer_protocol.OpenReply)) return null;
+    var packet: [usb_transfer_protocol.message_maximum]u8 = undefined;
-    const open_reply = std.mem.bytesToValue(usb_transfer_protocol.OpenReply, reply[0..@sizeOf(usb_transfer_protocol.OpenReply)]);
+    const framed = Protocol.encodeRequest(.open, device_id, {}, &.{}, &packet) orelse return null;
-    if (open_reply.status != 0) return null;
+    var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
+    const result = ipc.callCap(bus, framed, &reply, endpoint) catch return null;
+    const answered = reply[0..result.len];
+    const status = envelope.statusOf(answered) orelse return null;
+    if (status.status != 0) return null;
+    const open_reply = Protocol.decodeReply(.open, answered) orelse return null;
 
     var device = Device{
         .bus = bus,

library/kernel/build.zig

@@ -0,0 +1,143 @@
+//! The "kernel" library domain (library/kernel): the userspace private-ABI
+//! library (kernel32-style), split by concern into directly-importable
+//! modules. The graph is a DAG: memory depends on thread (heap needs
+//! Thread.Mutex), and thread does its own raw mmap so there is no cycle.
+//!
+//! This package also exports `abi` — the kernel <-> user contract (SystemCall
+//! numbers, mmap prot flags, page_size). Its source lives with the kernel in
+//! system/abi.zig, outside this directory, but userspace's one view of it is
+//! exported here so every consumer names the same module instance. Reaching
+//! outside the package root means this package is valid only as an in-repo
+//! path dependency (never fetchable by hash) — fine, since path dependencies
+//! are the only way danos packages are consumed.
+//!
+//! The root shim (root.zig) and the user link script (user.ld) are plain
+//! files, not modules; build-support reaches them through this package's
+//! directory (Dependency.path).
+
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    const protocol = b.dependency("protocol", .{});
+
+    const abi = b.addModule("abi", .{
+        .root_source_file = b.path("../../system/abi.zig"),
+    });
+    const system_call = b.addModule("system-call", .{
+        .root_source_file = b.path("system-call.zig"),
+        .imports = &.{.{ .name = "abi", .module = abi }},
+    });
+    const ipc = b.addModule("ipc", .{
+        .root_source_file = b.path("ipc.zig"),
+        .imports = &.{ .{ .name = "abi", .module = abi }, .{ .name = "system-call", .module = system_call } },
+    });
+    const time = b.addModule("time", .{
+        .root_source_file = b.path("time.zig"),
+        .imports = &.{.{ .name = "system-call", .module = system_call }},
+    });
+    const thread = b.addModule("thread", .{
+        .root_source_file = b.path("thread.zig"),
+        .imports = &.{ .{ .name = "abi", .module = abi }, .{ .name = "system-call", .module = system_call } },
+    });
+    const logging = b.addModule("logging", .{
+        .root_source_file = b.path("logging.zig"),
+        .imports = &.{ .{ .name = "abi", .module = abi }, .{ .name = "system-call", .module = system_call } },
+    });
+    const process = b.addModule("process", .{
+        .root_source_file = b.path("process.zig"),
+        .imports = &.{
+            .{ .name = "abi", .module = abi },
+            .{ .name = "system-call", .module = system_call },
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "time", .module = time },
+        },
+    });
+    const file_system = b.addModule("file-system", .{
+        .root_source_file = b.path("file-system.zig"),
+        .imports = &.{
+            .{ .name = "abi", .module = abi },
+            .{ .name = "system-call", .module = system_call },
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "vfs-protocol", .module = protocol.module("vfs-protocol") },
+            .{ .name = "envelope", .module = protocol.module("envelope") },
+        },
+    });
+    // The channel is the L1 concept made concrete (docs/os-development/communication.md):
+    // it needs the namespace (file-system, to resolve a /protocol name) and the
+    // transport (ipc) both, which is why it lives here rather than in a protocol
+    // module — those import nothing.
+    const channel = b.addModule("channel", .{
+        .root_source_file = b.path("channel.zig"),
+        .imports = &.{
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "time", .module = time },
+            .{ .name = "file-system", .module = file_system },
+            .{ .name = "vfs-protocol", .module = protocol.module("vfs-protocol") },
+            .{ .name = "envelope", .module = protocol.module("envelope") },
+        },
+    });
+    _ = b.addModule("memory", .{
+        .root_source_file = b.path("memory/memory.zig"),
+        .imports = &.{
+            .{ .name = "abi", .module = abi },
+            .{ .name = "system-call", .module = system_call },
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "thread", .module = thread },
+        },
+    });
+    // The harness binds the service's contract name at startup, which is a
+    // conversation with the registry — hence channel (and time, for the patience
+    // a provider that beat init to the mount needs). It also owns the subscriber
+    // table and the fan-out, which are expressed in the envelope's vocabulary
+    // (the reserved subscribe verb, the push floor) — hence envelope.
+    _ = b.addModule("service", .{
+        .root_source_file = b.path("service.zig"),
+        .imports = &.{
+            .{ .name = "channel", .module = channel },
+            .{ .name = "envelope", .module = protocol.module("envelope") },
+            .{ .name = "ipc", .module = ipc },
+            .{ .name = "process", .module = process },
+        },
+    });
+    _ = b.addModule("start", .{
+        .root_source_file = b.path("start.zig"),
+        .imports = &.{ .{ .name = "process", .module = process }, .{ .name = "logging", .module = logging } },
+    });
+
+    // Standalone `zig build test` for this domain alone; the root build keeps
+    // its aggregate test step. time and thread pull in the syscall wrappers,
+    // which need the `abi` module; their danos seams fall back to host
+    // primitives off the danos target, so they run with real host threads.
+    const test_step = b.step("test", "Run the kernel library unit tests");
+    for ([_][]const u8{
+        "time.zig", // Instant/Duration arithmetic
+        "thread.zig", // Mutex/Condition/RwLock/WaitGroup state machines
+    }) |root| {
+        const kernel_tests = b.addTest(.{
+            .root_module = b.createModule(.{
+                .root_source_file = b.path(root),
+                .target = b.resolveTargetQuery(.{}),
+                .imports = &.{.{ .name = "abi", .module = abi }},
+            }),
+        });
+        test_step.dependOn(&b.addRunArtifact(kernel_tests).step);
+    }
+
+    // channel needs its whole import set to compile at all; only its framing is
+    // host-runnable (the syscall seams are x86_64-only, and unreferenced from
+    // the tests), so that is what it tests.
+    const channel_tests = b.addTest(.{
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("channel.zig"),
+            .target = b.resolveTargetQuery(.{}),
+            .imports = &.{
+                .{ .name = "ipc", .module = ipc },
+                .{ .name = "time", .module = time },
+                .{ .name = "file-system", .module = file_system },
+                .{ .name = "vfs-protocol", .module = protocol.module("vfs-protocol") },
+                .{ .name = "envelope", .module = protocol.module("envelope") },
+            },
+        }),
+    });
+    test_step.dependOn(&b.addRunArtifact(channel_tests).step);
+}

library/kernel/build.zig.zon

@@ -0,0 +1,11 @@
+.{
+    .name = .kernel,
+    .version = "0.0.0",
+    .fingerprint = 0x5dd29aab36503453, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{
+        // file-system speaks the VFS wire protocol.
+        .protocol = .{ .path = "../protocol" },
+    },
+    .paths = .{""},
+}

library/kernel/channel.zig

@@ -0,0 +1,339 @@
+//! `Channel` — layer L1 of the communication stack
+//! (docs/os-development/communication.md) made concrete. A program holds a
+//! channel that speaks a protocol; it does not hold a raw handle and marshal
+//! bytes at one. The channel is the answer to "who am I talking to", decided
+//! once at establishment, so nothing after that ever routes a party again:
+//! every packet's `target` addresses an *object* within the peer already chosen.
+//!
+//! **Possession of the Channel is the connection.** There is no connect step, no
+//! session id, no reconnect handshake — the endpoint capability inside is the
+//! whole of the relationship, and it cannot be forged, only handed over. Which
+//! also means a channel is a resource: `close` it, or it occupies a handle-table
+//! slot for the life of the process.
+//!
+//! **A dead provider surfaces as `-EPEER`, and the recovery is to re-open.**
+//! When the process on the other end exits, the kernel fails calls on its
+//! endpoint rather than blocking forever; `call` returns null. The client does
+//! not repair the channel — it discards it and opens the name again, which
+//! reaches whatever instance the registry now points at. The restart story
+//! falls out of the naming layer for free; no protocol needs a reconnect verb.
+//!
+//! `open` resolves a `/protocol/<name>` path through the kernel VFS router and
+//! takes the provider's endpoint from the open reply's capability. The registry
+//! answering it is init, PID 1, which mounts `/protocol` before it spawns anyone
+//! (docs/os-development/protocol-namespace.md); `bind` below is the other half —
+//! how a provider claims the name in the first place.
+
+const std = @import("std");
+const ipc = @import("ipc");
+const time = @import("time");
+const file_system = @import("file-system");
+const vfs_protocol = @import("vfs-protocol");
+const envelope = @import("envelope");
+
+/// Longest `/protocol/...` path this client marshals. The registry's names are
+/// short by construction (a contract leaf, not a file path), and the buffer is
+/// on the stack of whoever opens.
+pub const path_maximum: usize = 224;
+
+/// Where the protocol namespace is rooted — the one path prefix in the system
+/// that names contracts rather than files. Spelled once, here, so no caller
+/// builds it by hand (docs/file-system-development/file-system-hierarchy.md).
+pub const root: []const u8 = "/protocol";
+
+/// Longest contract name — the part after `/protocol/`. Short by construction:
+/// a leaf like `display`, or a subtree leaf like `test/shared-memory`.
+pub const name_maximum: usize = 64;
+
+/// What a `call` came back with: the provider's status, the reply payload (the
+/// bytes after the `Status`, in the caller's own buffer), and any capability the
+/// reply carried.
+pub const Response = struct {
+    status: envelope.Status,
+    payload: []u8,
+    capability: ?ipc.Handle,
+
+    /// Whether the provider answered success. A negative status is its refusal
+    /// (`-ENOSYS` for a verb it does not implement, and so on).
+    pub fn succeeded(self: Response) bool {
+        return self.status.status == 0;
+    }
+};
+
+/// An open conversation with one provider, speaking one protocol.
+pub const Channel = struct {
+    /// The provider's endpoint. Sending into it is the only thing this handle
+    /// can do — an endpoint is a mailbox owned by its creator, and that
+    /// direction never reverses.
+    endpoint: ipc.Handle,
+
+    /// Adopt an endpoint that arrived some other way — a capability delivered
+    /// in a reply, or one a supervisor wired in at spawn time (P5). The channel
+    /// takes ownership of the handle.
+    pub fn adopt(endpoint: ipc.Handle) Channel {
+        return .{ .endpoint = endpoint };
+    }
+
+    /// Establish a channel by name: resolve `/protocol/<name>` to the registry
+    /// backend, `open` the contract there, and take the provider's endpoint from
+    /// the reply's capability. Null if the path does not resolve, the registry
+    /// refuses (an ungranted name is refused *as* not-found), or the reply
+    /// carries no capability.
+    ///
+    /// The path is spoken exactly once, here. Everything afterwards is integers
+    /// in the packet header.
+    pub fn open(path: []const u8) ?Channel {
+        return .{ .endpoint = openPath(path) orelse return null };
+    }
+
+    /// Establish a channel by contract name — `open` with `/protocol/` supplied,
+    /// which is how every caller in the system spells it.
+    pub fn connect(name: []const u8) ?Channel {
+        return .{ .endpoint = openEndpoint(name) orelse return null };
+    }
+
+    /// Send one request packet and block for the reply: `[Header][request]` out,
+    /// `[Status][reply]` back. `request` is the bytes *after* the header — the
+    /// protocol's fixed part plus any tail — because the header is this call's
+    /// to lay down. The reply's payload lands in `into`.
+    ///
+    /// Null means the transport failed, which today means one of: a dead
+    /// provider (`-EPEER` — discard this channel and `open` the name again), an
+    /// oversized packet, or a bad handle. A provider that answered *and refused*
+    /// is not a failure here: it comes back with a negative `Response.status`.
+    pub fn call(self: Channel, header: envelope.Header, request: []const u8, into: []u8) ?Response {
+        return self.callCapability(header, request, into, null);
+    }
+
+    /// As `call`, handing the provider a capability with the request — the only
+    /// direction-crossing move kernel-ipc offers, and how `subscribe` delivers
+    /// the subscriber's own endpoint.
+    pub fn callCapability(
+        self: Channel,
+        header: envelope.Header,
+        request: []const u8,
+        into: []u8,
+        capability: ?ipc.Handle,
+    ) ?Response {
+        var packet: [envelope.packet_maximum]u8 = undefined;
+        const framed = frame(header, request, &packet) orelse return null;
+
+        var reply: [envelope.packet_maximum]u8 = undefined;
+        const answer = ipc.callCap(self.endpoint, framed, &reply, capability) catch return null;
+        const status = envelope.statusOf(reply[0..answer.len]) orelse return null;
+        const available = @min(answer.len - envelope.prefix_size, @as(usize, status.len));
+        const taken = @min(available, into.len);
+        @memcpy(into[0..taken], reply[envelope.prefix_size..][0..taken]);
+        return .{ .status = status, .payload = into[0..taken], .capability = answer.cap };
+    }
+
+    /// Push one event packet and return immediately — no reply owed, and a slow
+    /// or dead peer can never stall the sender. Bounded by `post_maximum`: an
+    /// event that does not fit is refused here rather than split, because a
+    /// packet is never fragmented.
+    pub fn send(self: Channel, header: envelope.Header, payload: []const u8) bool {
+        var packet: [envelope.post_maximum]u8 = undefined;
+        const framed = frame(header, payload, &packet) orelse return false;
+        return ipc.send(self.endpoint, framed);
+    }
+
+    /// Ask the provider what it is: the reserved `describe` verb, answered by
+    /// every protocol built through `envelope.Define`. The name and version come
+    /// back in `into`, which the returned `Described` borrows.
+    pub fn describe(self: Channel, into: []u8) ?envelope.Described {
+        var request: [envelope.packet_maximum]u8 = undefined;
+        const packet = envelope.encodeDescribe(&request) orelse return null;
+
+        var reply: [envelope.packet_maximum]u8 = undefined;
+        const answer = ipc.callCap(self.endpoint, packet, &reply, null) catch return null;
+        const taken = @min(answer.len, into.len);
+        @memcpy(into[0..taken], reply[0..taken]);
+        return envelope.decodeDescribe(into[0..taken]);
+    }
+
+    /// Drop the provider's endpoint and free the handle-table slot. The
+    /// conversation is over the moment the capability is gone — there is nothing
+    /// else holding it open.
+    pub fn close(self: Channel) void {
+        _ = ipc.close(self.endpoint);
+    }
+};
+
+// --- the namespace: resolving, opening, and claiming a contract name ---------
+
+/// Where a `/protocol/...` path routed: the registry's endpoint, plus the path
+/// rewritten mount-relative (`/display` for `/protocol/display`). The handle is
+/// deduplicated by the kernel across resolves and shared with every other user
+/// of that mount, so it is never ours to close.
+const Registry = struct {
+    handle: ipc.Handle,
+    relative: [path_maximum]u8,
+    relative_len: usize,
+
+    fn path(self: *const Registry) []const u8 {
+        return self.relative[0..self.relative_len];
+    }
+};
+
+/// Route `path` to whatever backend serves it. Null when nothing is mounted
+/// there — under `/protocol` that means the registry is not up yet, which is a
+/// *retry*, not a refusal. A kernel-served route (the read-only `/system` tree)
+/// is the wrong path, not a channel, and is refused here.
+fn reach(path: []const u8) ?Registry {
+    var out: Registry = .{ .handle = 0, .relative = undefined, .relative_len = 0 };
+    const route = file_system.fsResolve(path, 0, &out.relative) orelse return null;
+    switch (route) {
+        .kernel => return null,
+        .backend => |b| {
+            out.handle = b.handle;
+            out.relative_len = b.path_len;
+            return out;
+        },
+    }
+}
+
+/// One vfs-protocol round trip at a backend: the folded header, the verb's own
+/// fixed part, the name as the packet's tail, and an optional capability in each
+/// direction. Both verbs this file sends address the backend itself (target 0) —
+/// the name in the tail is what they are about.
+fn transact(
+    comptime operation: vfs_protocol.Operation,
+    handle: ipc.Handle,
+    request: vfs_protocol.Protocol.RequestOf(operation),
+    name: []const u8,
+    send_capability: ?ipc.Handle,
+) ?struct { status: envelope.Status, capability: ?ipc.Handle } {
+    var packet: [vfs_protocol.message_maximum]u8 = undefined;
+    const framed = vfs_protocol.Protocol.encodeRequest(operation, 0, request, name, &packet) orelse return null;
+
+    var reply: [vfs_protocol.message_maximum]u8 = undefined;
+    const answer = ipc.callCap(handle, framed, &reply, send_capability) catch return null;
+    const status = envelope.statusOf(reply[0..answer.len]) orelse return null;
+    return .{ .status = status, .capability = answer.cap };
+}
+
+/// Resolve an absolute `/protocol/...` path and take the provider's endpoint out
+/// of the open reply's capability.
+fn openPath(path: []const u8) ?ipc.Handle {
+    const registry = reach(path) orelse return null;
+    const answered = transact(.open, registry.handle, .{ .flags = 0 }, registry.path(), null) orelse return null;
+    if (answered.status.status != 0) {
+        // A refusal carries no channel; anything that arrived anyway would be a
+        // handle-table slot spent for nothing.
+        if (answered.capability) |handle| _ = ipc.close(handle);
+        return null;
+    }
+    // The capability *is* the channel — an open that succeeds without one was
+    // answered by a file backend, which does not speak protocols.
+    return answered.capability;
+}
+
+/// The provider's raw endpoint behind `/protocol/<name>`. The transitional form,
+/// for the clients that still marshal their protocol's bytes by hand; P4 moves
+/// them onto `Channel` proper and this shrinks back to `connect`.
+///
+/// Null covers both "no such contract" and "you may not have it" — deliberately
+/// the same answer (protocol-namespace.md: enforcement is absence), and also
+/// "the registry is not mounted yet", which is why every caller retries.
+pub fn openEndpoint(name: []const u8) ?ipc.Handle {
+    var path: [path_maximum]u8 = undefined;
+    const full = join(name, &path) orelse return null;
+    return openPath(full);
+}
+
+/// Claim `/protocol/<name>` for `endpoint`: the registry records the name
+/// against this process and hands the endpoint to whoever opens it afterwards.
+/// The endpoint rides the call as its capability, the one direction-crossing
+/// move kernel-ipc offers.
+///
+/// Three-valued on purpose. **Null** is "the registry could not be reached" —
+/// it is not mounted yet, which happens when a provider starts before init has
+/// finished coming up, and the answer is to retry. A **value** is the registry's
+/// verdict and is final: 0 bound, `-EPERM` this binary is not granted that name,
+/// `-EBUSY` a live provider already holds it.
+pub fn bind(name: []const u8, endpoint: ipc.Handle) ?i32 {
+    const registry = reach(root) orelse return null;
+    const answered = transact(.bind, registry.handle, {}, name, endpoint) orelse return null;
+    return answered.status.status;
+}
+
+/// How long a provider keeps offering itself before giving up. The registry is
+/// init, which mounts `/protocol` before it spawns anyone, so in a normal boot
+/// the first try lands; a provider the kernel test harness starts may well beat
+/// init to the mount, which is what the patience is for. Four seconds of 20 ms
+/// tries — the same cadence every client in the tree spends finding a service.
+const bind_attempts: u32 = 200;
+const bind_retry_ms: u64 = 20;
+
+/// `bind`, waiting out a registry that is not mounted yet. Only unreachability
+/// is retried: a registry that *answered* has decided, and asking again cannot
+/// change its mind. True when the name is ours.
+pub fn bindPatiently(name: []const u8, endpoint: ipc.Handle) bool {
+    var attempt: u32 = 0;
+    while (attempt < bind_attempts) : (attempt += 1) {
+        if (bind(name, endpoint)) |status| return status == 0;
+        time.sleepMillis(bind_retry_ms);
+    }
+    return false;
+}
+
+/// `/protocol/` + `name`, in the caller's buffer. Null if the name is empty or
+/// longer than the namespace admits.
+fn join(name: []const u8, buffer: []u8) ?[]u8 {
+    if (name.len == 0 or name.len > name_maximum) return null;
+    const total = root.len + 1 + name.len;
+    if (total > buffer.len) return null;
+    @memcpy(buffer[0..root.len], root);
+    buffer[root.len] = '/';
+    @memcpy(buffer[root.len + 1 ..][0..name.len], name);
+    return buffer[0..total];
+}
+
+/// Lay a packet down: the folded header first, then the protocol's bytes. Null
+/// when it would not fit the buffer — the same rule as `envelope`'s framing,
+/// applied where the buffer is the transport's, not the protocol's.
+fn frame(header: envelope.Header, body: []const u8, buffer: []u8) ?[]u8 {
+    const total = envelope.prefix_size + body.len;
+    if (total > buffer.len) return null;
+    @memcpy(buffer[0..envelope.prefix_size], std.mem.asBytes(&header));
+    @memcpy(buffer[envelope.prefix_size..][0..body.len], body);
+    return buffer[0..total];
+}
+
+// --- tests ------------------------------------------------------------------
+//
+// The syscall half cannot run on the host, and there is no registry to reach
+// until P2 — so what is testable here is the framing, which is the part with
+// arithmetic in it.
+
+const testing = std.testing;
+
+test "a framed packet is the header followed by the protocol's bytes" {
+    var buffer: [envelope.packet_maximum]u8 = undefined;
+    const header = envelope.Header{ .operation = envelope.first_protocol_operation, .target = 9 };
+    const packet = frame(header, "body", &buffer).?;
+
+    try testing.expectEqual(envelope.prefix_size + "body".len, packet.len);
+    const decoded = envelope.headerOf(packet).?;
+    try testing.expectEqual(envelope.first_protocol_operation, decoded.operation);
+    try testing.expectEqual(@as(u64, 9), decoded.target);
+    try testing.expectEqualStrings("body", packet[envelope.prefix_size..]);
+}
+
+test "a contract name joins the namespace root exactly once" {
+    var buffer: [path_maximum]u8 = undefined;
+    try testing.expectEqualStrings("/protocol/display", join("display", &buffer).?);
+    try testing.expectEqualStrings("/protocol/test/shared-memory", join("test/shared-memory", &buffer).?);
+    try testing.expect(join("", &buffer) == null);
+    try testing.expect(join("x" ** (name_maximum + 1), &buffer) == null);
+}
+
+test "framing refuses a packet that would not fit rather than truncating it" {
+    var post: [envelope.post_maximum]u8 = undefined;
+    const header = envelope.Header{ .operation = envelope.first_protocol_operation };
+    const body = [_]u8{0} ** (envelope.post_maximum - envelope.prefix_size);
+    const one_too_many = body ++ [_]u8{0};
+
+    try testing.expect(frame(header, &body, &post) != null);
+    try testing.expect(frame(header, &one_too_many, &post) == null);
+}

library/kernel/file-system.zig

@@ -14,8 +14,13 @@ const std = @import("std");
 const abi = @import("abi");
 const sc = @import("system-call");
 const ipc = @import("ipc");
+const envelope = @import("envelope");
 const vfs_protocol = @import("vfs-protocol");
 
+/// The generated vfs contract: encode/decode for every verb, with the node id
+/// carried in the packet header's `target`.
+const Protocol = vfs_protocol.Protocol;
+
 /// The kind of a filesystem node — re-exported so a caller need not import the
 /// wire protocol.
 pub const Kind = vfs_protocol.NodeKind;
@@ -39,6 +44,7 @@ fn kindFromWire(value: u32) Kind {
         @intFromEnum(Kind.symbolic_link) => .symbolic_link,
         @intFromEnum(Kind.fifo) => .fifo,
         @intFromEnum(Kind.socket) => .socket,
+        @intFromEnum(Kind.protocol) => .protocol,
         else => .regular,
     };
 }
@@ -88,23 +94,24 @@ fn resolve(path: []const u8, flags: usize) ?Route {
     }
 }
 
-const Result = struct { reply: vfs_protocol.Reply, payload: []u8 };
+// One request/reply round trip: frame `[Header][request][tail]`, send it, and
-
+// hand back the whole reply packet for the caller to decode with the generated
-// One request/reply round trip: [Request header][send payload] -> backend ->
+// helpers. A backend that refused (a negative status) reads as null, which is
-// [Reply header][receive payload]. The receive payload lands in `out`.
+// what every caller here did with it anyway.
-fn transact(h: ipc.Handle, request: vfs_protocol.Request, send: []const u8, out: []u8) ?Result {
+fn transact(
-    var message: [vfs_protocol.message_maximum]u8 = undefined;
+    comptime operation: Protocol.Operation,
-    @memcpy(message[0..vfs_protocol.request_size], std.mem.asBytes(&request));
+    handle: ipc.Handle,
-    const slen = @min(send.len, vfs_protocol.maximum_payload);
+    target: u64,
-    @memcpy(message[vfs_protocol.request_size..][0..slen], send[0..slen]);
+    request: Protocol.RequestOf(operation),
-
+    tail: []const u8,
-    var rbuf: [vfs_protocol.message_maximum]u8 = undefined;
+    reply: []u8,
-    const n = ipc.call(h, message[0 .. vfs_protocol.request_size + slen], &rbuf) catch return null;
+) ?[]u8 {
-    if (n < vfs_protocol.reply_size) return null;
+    var packet: [vfs_protocol.message_maximum]u8 = undefined;
-    const reply = std.mem.bytesToValue(vfs_protocol.Reply, rbuf[0..vfs_protocol.reply_size]);
+    const framed = Protocol.encodeRequest(operation, target, request, tail, &packet) orelse return null;
-    const rpl = @min(n - vfs_protocol.reply_size, out.len);
+    const n = ipc.call(handle, framed, reply) catch return null;
-    @memcpy(out[0..rpl], rbuf[vfs_protocol.reply_size..][0..rpl]);
+    const status = envelope.statusOf(reply[0..n]) orelse return null;
-    return .{ .reply = reply, .payload = out[0..rpl] };
+    if (status.status != 0) return null;
+    return reply[0..n];
 }
 
 /// An open file: a VFS node plus a byte cursor. Read and write advance the cursor.
@@ -124,11 +131,13 @@ pub const File = struct {
             return n;
         };
         const want: u32 = @intCast(@min(buffer.len, vfs_protocol.maximum_payload));
-        const request = vfs_protocol.Request{ .operation = .read, .node = self.node, .offset = self.offset, .len = want, .flags = 0 };
+        var reply: [vfs_protocol.message_maximum]u8 = undefined;
-        const r = transact(h, request, &.{}, buffer) orelse return null;
+        const answered = transact(.read, h, self.node, .{ .offset = self.offset, .len = want }, &.{}, &reply) orelse return null;
-        if (r.reply.status != 0) return null;
+        const bytes = Protocol.replyTail(.read, answered);
-        self.offset += r.reply.len;
+        const n = @min(bytes.len, buffer.len);
-        return r.reply.len;
+        @memcpy(buffer[0..n], bytes[0..n]);
+        self.offset += n;
+        return n;
     }
 
     /// Write `data` at the current offset; returns the count written. A single
@@ -138,11 +147,11 @@ pub const File = struct {
     pub fn write(self: *File, data: []const u8) ?usize {
         const h = self.backend orelse return null;
         const want: u32 = @intCast(@min(data.len, vfs_protocol.maximum_payload));
-        const request = vfs_protocol.Request{ .operation = .write, .node = self.node, .offset = self.offset, .len = want, .flags = 0 };
+        var reply: [vfs_protocol.message_maximum]u8 = undefined;
-        const r = transact(h, request, data[0..want], &.{}) orelse return null;
+        const answered = transact(.write, h, self.node, .{ .offset = self.offset, .len = want }, data[0..want], &reply) orelse return null;
-        if (r.reply.status != 0) return null;
+        const written = Protocol.decodeReply(.write, answered) orelse return null;
-        self.offset += r.reply.len;
+        self.offset += written.count;
-        return r.reply.len;
+        return written.count;
     }
 
     /// Write all of `data`, looping past the per-call payload cap. Returns the
@@ -168,11 +177,9 @@ pub const File = struct {
             const a = fsNodeStatus(self.node) orelse return null;
             return .{ .size = a.size, .kind = if (a.kind == file_kind_directory) .directory else .regular, .mtime = a.mtime };
         };
-        const request = vfs_protocol.Request{ .operation = .status, .node = self.node, .offset = 0, .len = 0, .flags = 0 };
+        var reply: [vfs_protocol.message_maximum]u8 = undefined;
-        var buffer: [@sizeOf(vfs_protocol.FileStatus)]u8 = undefined;
+        const answered = transact(.status, h, self.node, {}, &.{}, &reply) orelse return null;
-        const r = transact(h, request, &.{}, &buffer) orelse return null;
+        const status = Protocol.decodeReply(.status, answered) orelse return null;
-        if (r.reply.status != 0 or r.payload.len < @sizeOf(vfs_protocol.FileStatus)) return null;
-        const status = std.mem.bytesToValue(vfs_protocol.FileStatus, buffer[0..@sizeOf(vfs_protocol.FileStatus)]);
         return .{ .size = status.size, .kind = kindFromWire(status.kind), .mtime = status.mtime };
     }
 
@@ -180,8 +187,8 @@ pub const File = struct {
     /// tokens are permanent — nothing to release.
     pub fn close(self: *File) void {
         const h = self.backend orelse return;
-        const request = vfs_protocol.Request{ .operation = .close, .node = self.node, .offset = 0, .len = 0, .flags = 0 };
+        var reply: [vfs_protocol.message_maximum]u8 = undefined;
-        _ = transact(h, request, &.{}, &.{});
+        _ = transact(.close, h, self.node, {}, &.{}, &reply);
     }
 };
 
@@ -192,10 +199,10 @@ pub fn open(path: []const u8, options: OpenOptions) ?File {
         .kernel => |token| return .{ .node = token, .backend = null },
         .backend => |b| {
             const relative = route.backendPath();
-            const request = vfs_protocol.Request{ .operation = .open, .node = 0, .offset = 0, .len = @intCast(relative.len), .flags = options.wireFlags() };
+            var reply: [vfs_protocol.message_maximum]u8 = undefined;
-            const r = transact(b.handle, request, relative, &.{}) orelse return null;
+            const answered = transact(.open, b.handle, 0, .{ .flags = options.wireFlags() }, relative, &reply) orelse return null;
-            if (r.reply.status != 0) return null;
+            const opened = Protocol.decodeReply(.open, answered) orelse return null;
-            return .{ .node = r.reply.node, .backend = b.handle };
+            return .{ .node = opened.node, .backend = b.handle };
         },
     }
 }
@@ -247,15 +254,13 @@ pub const Directory = struct {
             self.cursor += 1;
             return true;
         };
-        const request = vfs_protocol.Request{ .operation = .readdir, .node = self.node, .offset = self.cursor, .len = 0, .flags = 0 };
+        var reply: [vfs_protocol.message_maximum]u8 = undefined;
-        var buffer: [vfs_protocol.message_maximum]u8 = undefined;
+        const answered = transact(.readdir, h, self.node, .{ .cursor = self.cursor }, &.{}, &reply) orelse return false;
-        const r = transact(h, request, &.{}, &buffer) orelse return false;
+        const header = Protocol.decodeReply(.readdir, answered) orelse return false;
-        if (r.reply.status != 0 or r.reply.len == 0) return false; // error or EOF
+        if (header.name_len == 0) return false; // end of directory
-        if (r.payload.len < vfs_protocol.directory_entry_size) return false;
-        const header = std.mem.bytesToValue(vfs_protocol.DirectoryEntry, r.payload[0..vfs_protocol.directory_entry_size]);
         entry.kind = kindFromWire(header.kind);
         entry.size = header.size;
-        const source = r.payload[vfs_protocol.directory_entry_size..];
+        const source = Protocol.replyTail(.readdir, answered);
         const nlen = @min(@min(@as(usize, header.name_len), source.len), entry.name_buffer.len);
         @memcpy(entry.name_buffer[0..nlen], source[0..nlen]);
         entry.name_len = nlen;
@@ -279,13 +284,11 @@ pub fn openDirectory(path: []const u8) ?Directory {
 // A path-based request that returns only a status (mkdir, unlink). Kernel-served
 // paths (the read-only /system) refuse mutation by construction: the resolve
 // must land on a backend.
-fn pathOperation(operation: vfs_protocol.Operation, path: []const u8) bool {
+fn pathOperation(comptime operation: Protocol.Operation, path: []const u8) bool {
     const route = resolve(path, 0) orelse return false;
     if (route != .backend) return false;
-    const relative = route.backendPath();
+    var reply: [vfs_protocol.message_maximum]u8 = undefined;
-    const request = vfs_protocol.Request{ .operation = operation, .node = 0, .offset = 0, .len = @intCast(relative.len), .flags = 0 };
+    return transact(operation, route.backend.handle, 0, {}, route.backendPath(), &reply) != null;
-    const r = transact(route.backend.handle, request, relative, &.{}) orelse return false;
-    return r.reply.status == 0;
 }
 
 /// Create a directory at `path` (its parent must already exist). Returns true on
@@ -305,7 +308,7 @@ pub fn makePath(path: []const u8) bool {
         while (end < path.len and path[end] != '/') end += 1;
         const prefix = path[0..end];
         if (prefix.len == 0 or (prefix.len == 1 and prefix[0] == '/')) continue;
-        // Best-effort per prefix: components at or above a mount point ("/mnt")
+        // Best-effort per prefix: components at or above a mount point ("/volumes")
         // are router names, not filesystem nodes — they neither exist as nodes
         // nor accept mkdir, and that is fine. Only the final verdict counts.
         if (!exists(prefix)) _ = makeDirectory(prefix);
@@ -335,9 +338,8 @@ pub fn rename(old_path: []const u8, new_path: []const u8) bool {
     @memcpy(payload[0..old_relative.len], old_relative);
     payload[old_relative.len] = 0;
     @memcpy(payload[old_relative.len + 1 ..][0..new_relative.len], new_relative);
-    const request = vfs_protocol.Request{ .operation = .rename, .node = 0, .offset = 0, .len = @intCast(total), .flags = 0 };
+    var reply: [vfs_protocol.message_maximum]u8 = undefined;
-    const r = transact(old_route.backend.handle, request, payload[0..total], &.{}) orelse return false;
+    return transact(.rename, old_route.backend.handle, 0, {}, payload[0..total], &reply) != null;
-    return r.reply.status == 0;
 }
 
 /// Mount a filesystem backend (its server endpoint) at absolute path `target`;
@@ -348,8 +350,9 @@ pub fn mount(target: []const u8, backend: ipc.Handle) bool {
 }
 
 /// As `mount`, with a backend-side rewrite prefix: a path under `target` reaches
-/// the backend as `rewrite` + the mount-relative tail. How one volume serves two
+/// the backend as `rewrite` + the mount-relative tail. How one volume serves
-/// mounts ("/mnt/usb" from its root, "/var" from its /var subtree).
+/// several mounts ("/volumes/usb" from its root, "/system/logs" from its
+/// /system/logs subtree).
 pub fn mountRewritten(target: []const u8, backend: ipc.Handle, rewrite: []const u8) bool {
     return fsMount(target, backend, rewrite);
 }

library/kernel/ipc.zig

@@ -29,16 +29,17 @@ pub fn createIpcEndpoint() ?Handle {
     return if (failed(r)) null else r;
 }
 
-/// Publish endpoint `h` under a well-known service id so other processes find it.
+// `register`/`lookup` lived here — the two wrappers over the flat ServiceId
-pub fn register(id: abi.ServiceId, h: Handle) bool {
+// registry. Naming is not a system call any more: a provider binds its contract
-    return !failed(sc.systemCall2(.ipc_register, @intFromEnum(id), h));
+// name at the registry and a client resolves and opens `/protocol/<name>`, both
-}
+// through `channel` (docs/os-development/protocol-namespace.md).
 
-/// Find the endpoint published under `id`, installing a handle to it in this
+/// Drop a capability handle (endpoint, shared-memory, or DMA-region) and free its table
-/// process.
+/// slot. A forwarding hop closes a cap it passed on; a binder closes a DMA-region cap
-pub fn lookup(id: abi.ServiceId) ?Handle {
+/// once the binding holds its own reference — the 32-slot table is otherwise consumed by
-    const r = sc.systemCall1(.ipc_lookup, @intFromEnum(id));
+/// repeated cap-passing.
-    return if (failed(r)) null else r;
+pub fn close(h: Handle) bool {
+    return !failed(sc.systemCall1(.handle_close, h));
 }
 
 pub const CallError = error{Failed};
@@ -170,6 +171,56 @@ pub const Received = struct {
     }
 };
 
+/// A capability that arrived with one turn of a receive loop, and the ownership
+/// rule for it: **the turn owns it until a handler takes it, and closes whatever
+/// is left.**
+///
+/// The kernel installs a sent capability in the receiver's handle table whenever
+/// the caller attached one, *independent of the message's length or kind*
+/// (system/kernel/ipc-synchronous.zig `replyWait`), so every path out of a loop
+/// has to dispose of one — including the paths that never look at the message.
+/// The table is thirty-two slots, and `ipc_call` does not dedupe, so a client
+/// looping on `callCap(server, &.{}, endpoint)` spends one slot per call: about
+/// thirty-two zero-length pings and the service can never accept another
+/// capability, which means no subscribe and no shared-memory handover, for the
+/// rest of the boot. It is unauthenticated and it is two lines to write.
+///
+/// So ownership is structural rather than a close per branch — the per-branch
+/// version has already failed twice in this tree, in PID 1's ping path and in
+/// every `service.run` callback that simply ignored its capability argument.
+/// Written this way, forgetting **closes**, and *keeping* a capability is the
+/// thing a handler has to say out loud:
+///
+/// ```zig
+/// var arrived: ipc.Arrival = .{ .handle = got.cap };
+/// defer arrived.release();          // every exit path, including `continue`
+/// ...
+/// const kept = arrived.take().?;    // claimed: mine to hold or close
+/// ```
+pub const Arrival = struct {
+    handle: ?Handle = null,
+
+    /// Look without claiming — a handler that may still refuse wants no close of
+    /// its own on the refusal paths.
+    pub fn peek(self: *const Arrival) ?Handle {
+        return self.handle;
+    }
+
+    /// Claim ownership: from here the capability is the taker's to keep or close,
+    /// and the turn will not touch it.
+    pub fn take(self: *Arrival) ?Handle {
+        defer self.handle = null;
+        return self.handle;
+    }
+
+    /// Close whatever nobody claimed. Idempotent, so it is safe as a `defer` next
+    /// to any number of `take`s.
+    pub fn release(self: *Arrival) void {
+        if (self.handle) |handle| _ = close(handle);
+        self.handle = null;
+    }
+};
+
 /// Server side of IPC_ReplyWait: deliver `reply` to the client last received (if any,
 /// optionally handing it `send_cap`), then block until the next request arrives in
 /// `receive`. Returns its length, the sender badge, and any capability the request

library/kernel/memory/dma.zig

@@ -12,12 +12,18 @@ const sc = @import("system-call");
 pub const coherent: usize = abi.dma_coherent;
 pub const write_combining: usize = abi.dma_write_combining;
 pub const below_4g: usize = abi.dma_below_4g;
+/// Ask for a capability handle (in `Region.handle`) so the buffer can be delegated to
+/// another driver and bound into a device's IOMMU domain (`driver.dmaBind`). A driver's
+/// private rings don't need it; a buffer whose physical address crosses IPC does.
+pub const shareable: usize = abi.dma_shareable;
 
-/// A DMA allocation: the `virtual` address the CPU touches, and the `physical` address
+/// A DMA allocation: the `virtual` address the CPU touches, the `physical` address to
-/// to program into the device's descriptor-ring / base registers.
+/// program into the device's registers, and — when `shareable` was requested — a
+/// capability `handle` naming the region for delegation (null otherwise).
 pub const Region = struct {
     virtual: usize,
     physical: usize,
+    handle: ?usize = null,
 };
 
 inline fn failed(r: usize) bool {
@@ -25,21 +31,23 @@ inline fn failed(r: usize) bool {
 }
 
 /// Allocate `len` bytes of DMA-capable memory with `flags` (e.g. `coherent`, or
-/// `coherent | below_4g`). Returns the virtual/physical pair, or null on failure. Two
+/// `coherent | shareable`). Returns virtual/physical (and a handle when `shareable`), or
-/// return values — the virtual address in rax, the physical address in rdx — so it
+/// null on failure. Three return values — virtual in rax, physical in rdx, handle in r8
-/// needs a hand-written stub.
+/// — so it needs a hand-written stub.
 pub fn alloc(len: usize, flags: usize) ?Region {
     var rax: usize = undefined;
     var rdx: usize = undefined; // out: physical address
+    var r8: usize = undefined; // out: capability handle (abi.no_cap unless shareable)
     asm volatile ("syscall"
         : [rax] "={rax}" (rax),
           [rdx] "={rdx}" (rdx),
+          [r8] "={r8}" (r8),
         : [n] "{rax}" (@intFromEnum(abi.SystemCall.dma_alloc)),
           [a0] "{rdi}" (len),
           [a1] "{rsi}" (flags),
         : .{ .rcx = true, .r11 = true, .memory = true });
     if (failed(rax)) return null;
-    return .{ .virtual = rax, .physical = rdx };
+    return .{ .virtual = rax, .physical = rdx, .handle = if (r8 == abi.no_cap) null else r8 };
 }
 
 /// Release a region from a prior `alloc` (`virtual` and the same `len`).

library/kernel/memory/memory.zig

@@ -38,6 +38,7 @@ pub const DmaRegion = dma.Region;
 pub const dma_coherent = dma.coherent;
 pub const dma_write_combining = dma.write_combining;
 pub const dma_below_4g = dma.below_4g;
+pub const dma_shareable = dma.shareable;
 pub const dmaAlloc = dma.alloc;
 pub const dmaFree = dma.free;
 

library/kernel/process.zig

@@ -142,6 +142,18 @@ pub fn subscribeExits(endpoint: usize) bool {
 /// snapshot buffer without importing `abi` itself.
 pub const ProcessDescriptor = abi.ProcessDescriptor;
 
+/// The calling task's own kernel id — its row in the process table, and the value
+/// every other process sees as this one's `supervisor` after it spawns them. For a
+/// single-threaded program that is its process id; in a threaded one it is the
+/// calling thread's id (`Thread.getCurrentId` is the same system call, named for
+/// the threading vocabulary). Ids are monotonic and never reused
+/// (system/kernel/process.zig), which is what makes comparing one an identity
+/// test where comparing a *name* is only a resemblance test — the registrar in
+/// init leans on exactly that.
+pub fn taskId() u32 {
+    return @intCast(sc.systemCall0(.thread_self));
+}
+
 /// Give up the rest of this quantum.
 pub fn yield() void {
     _ = sc.systemCall0(.yield);

library/kernel/service.zig

@@ -6,26 +6,64 @@
 //! loop chose, never on a hijacked stack — the whole reason signals are
 //! messages.
 //!
+//! One rule a service author does have to know, and it is stated on
+//! `Callbacks.on_message`: **a capability that arrives belongs to the turn** —
+//! the loop closes it unless the callback claims it with `take()`. Forgetting is
+//! therefore safe, and keeping is explicit; the opposite arrangement quietly
+//! spends a handle-table slot per request.
+//!
+//! The harness also owns the **subscriber side** of a protocol that declares
+//! `.events` — see `Subscribers`. The table, the reserved subscribe/unsubscribe
+//! verbs, the fan-out, and the dead-subscriber sweep live here rather than in
+//! each provider, so every event stream in the system has identical semantics
+//! (docs/os-development/protocol-namespace.md, "Wiring").
+//!
 //! The liveness probe: a **zero-length request is the universal ping**, answered
 //! with a zero-length reply by the harness itself. No protocol's requests start
 //! at length zero, so the encoding cannot collide, and there is nothing for a
 //! service author to implement — a wedged service simply fails to answer, which
 //! is the diagnosis (see docs/ipc.md).
 
-const abi = @import("abi");
+const channel = @import("channel");
+const envelope = @import("envelope");
 const ipc = @import("ipc");
 const process = @import("process");
 
+/// The harness's handle on a provider's subscriber table, type-erased because
+/// `run` is not generic over the protocol while `Subscribers` is. A service names
+/// its table once, as `Callbacks.subscribers`, and the loop does the rest: it
+/// subscribes to published process exits at startup and drops a dead task's
+/// subscriptions before the service's own notification callback ever sees the
+/// badge.
+pub const SubscriberHooks = struct {
+    /// Ask the kernel for published exit events on this service's endpoint.
+    watch: *const fn (endpoint: ipc.Handle) void,
+    /// Drop everything task `dead` had subscribed.
+    forget: *const fn (dead: u32) void,
+};
+
 pub const Callbacks = struct {
     /// Called once with the service's endpoint before the loop starts — the
     /// place to subscribe to exit events, bind IRQs, or announce readiness.
     /// Return false to abort startup (the process exits).
     init: ?*const fn (endpoint: ipc.Handle) bool = null,
     /// One protocol request from `sender` (a task id): write the reply into
-    /// `reply`, return its length. `capability` is the handle the request
+    /// `reply`, return its length. The zero-length ping never reaches this.
-    /// carried, if any (M13 cap passing — how a subscriber hands over its
+    ///
-    /// endpoint). The zero-length ping never reaches this.
+    /// `arrived` is the capability the request carried (M13 cap passing — how a
-    on_message: *const fn (message: []const u8, reply: []u8, sender: u32, capability: ?ipc.Handle) usize,
+    /// subscriber hands over its endpoint), and it comes with **an ownership
+    /// rule: the turn owns it, and a handler that wants to keep it must say so
+    /// with `take()`.** Whatever is left when this returns, the loop closes.
+    /// `peek()` reads it without claiming, which is what a handler that may
+    /// still refuse wants — no close of its own on the refusal paths.
+    ///
+    /// The rule is stated here, in the contract, because the alternative has
+    /// failed in practice: an implementation that simply ignored a `?ipc.Handle`
+    /// argument leaked a handle table slot per request, and every operation
+    /// except a subscribe ignores it. Thirty-two such requests — zero-length
+    /// pings will do, and they need no authorization — and the service can never
+    /// accept another capability for the rest of the boot. See `ipc.Arrival`.
+    on_message: *const fn (message: []const u8, reply: []u8, sender: u32, arrived: *ipc.Arrival) usize,
     /// A notification that is not a signal — a subscribed exit event, a bound
     /// IRQ, a timer landing. The raw badge; decode with the ipc helpers.
     on_notification: ?*const fn (badge: u64) void = null,
@@ -35,21 +73,238 @@ pub const Callbacks = struct {
     /// the return itself — never put *necessary* work here (iron rule 1: a kill
     /// arrives with no warning; this is for graceful extras only).
     on_terminate: ?*const fn () void = null,
-    /// Publish the endpoint under a well-known service id at startup.
+    /// The contract this service provides: a name under `/protocol`, mirroring
-    service: ?abi.ServiceId = null,
+    /// the `library/protocol/` module that defines the wire format — a program
+    /// imports `display-protocol` and the provider binds `"display"`
+    /// (docs/os-development/protocol-namespace.md). Bound at startup, before
+    /// `init` runs, so the service is reachable the moment it serves. A refusal
+    /// (not granted, or a live provider already holds the name) aborts startup.
+    service: ?[]const u8 = null,
+    /// This provider's subscriber table — `Subscribers(Protocol, Context).hooks`
+    /// — for a protocol that declares `.events`. Naming it here is what buys the
+    /// exit-notification sweep: the loop subscribes to published deaths at
+    /// startup and releases a dead subscriber's slot (and the endpoint capability
+    /// in it) when one lands.
+    subscribers: ?SubscriberHooks = null,
 };
 
-/// Run the service: create and (optionally) register the endpoint, bind signals
+/// How many subscribers one provider fans out to. Bounded like every table in
-/// to it, call `init`, then serve until `terminate` arrives — at which point the
+/// this system; a subscribe past the end is refused with `-ENOSPC` rather than
-/// loop returns and main's return is the clean exit the supervisor reads as
+/// silently forgetting an earlier one.
-/// `ExitReason.exited`. `maximum_message` sizes the receive and reply buffers
+pub const subscriber_capacity = 8;
-/// (a service passes its protocol's message maximum).
+
+/// The interest mask that means "every event of this protocol" — what a
+/// subscriber which named no class gets, and what a provider passes when the
+/// event it is publishing belongs to no class.
+pub const every_event: u32 = 0;
+
+/// The subscriber side of a protocol, for a provider whose contract declares
+/// `.events` (docs/os-development/protocol-namespace.md: *the harness owns the
+/// machinery — the subscriber table, the dead-subscriber sweep, and the fan-out
+/// loop*). Three services hand-rolled this, with three different ideas of when a
+/// dead subscriber goes away — a poll of the process list on subscribe, a drop on
+/// a failed send, and nothing at all. This is the one idiom.
+///
+/// ```zig
+/// const Subscriptions = service.Subscribers(power_protocol.Protocol, void);
+/// ...
+/// fn onMessage(message: []const u8, reply: []u8, sender: u32, arrived: *ipc.Arrival) usize {
+///     return Subscriptions.dispatch({}, handlers, message, sender, arrived, reply);
+/// }
+/// pub fn main() void {
+///     service.run(power_protocol.message_maximum, .{
+///         .service = "power",
+///         .on_message = onMessage,
+///         .subscribers = Subscriptions.hooks,
+///     });
+/// }
+/// ```
+///
+/// What the provider still writes is its own events — `publish(.power_button, 0,
+/// .{})`. Everything else happens here: registering the caller's endpoint on the
+/// reserved `subscribe` verb, taking that capability out of the turn, dropping it
+/// on `unsubscribe` or on the subscriber's death, and framing one packet for the
+/// whole fan-out.
+///
+/// The table is per instantiation (a container-level `var` inside the generic
+/// type), so a process providing two contracts gets two tables and neither can
+/// see the other's subscribers.
+pub fn Subscribers(comptime Protocol: type, comptime Context: type) type {
+    return struct {
+        /// The generated dispatch this provider answers with.
+        pub const Provider = Protocol.Provider(Context);
+        pub const Handlers = Provider.Handlers;
+
+        /// One registered subscriber: the endpoint events are pushed to (the
+        /// capability it handed over at subscribe time, which this slot owns),
+        /// the task that handed it over — the kernel-stamped badge, the only
+        /// source identity there is — and which classes of event it asked for.
+        const Slot = struct {
+            used: bool = false,
+            endpoint: ipc.Handle = 0,
+            task: u32 = 0,
+            interest: u32 = every_event,
+        };
+
+        var slots: [subscriber_capacity]Slot = .{Slot{}} ** subscriber_capacity;
+
+        /// Set when a slot has taken the capability the turn carried, and read
+        /// back in `dispatch`, which is where the turn's `Arrival` lives. The
+        /// generated dispatch hands a handler the raw handle rather than the
+        /// `Arrival` — deliberately, since a handler has no business closing the
+        /// turn's property — so the *claim* has to travel back out this way. One
+        /// turn, one handler, one thread: there is nothing here to race.
+        var claimed = false;
+
+        /// What `Callbacks.subscribers` is given.
+        pub const hooks: SubscriberHooks = .{ .watch = watchExits, .forget = forget };
+
+        fn watchExits(endpoint: ipc.Handle) void {
+            // Published exits, not a poll of the process list: a service must
+            // never depend on clients cleaning up after themselves, and it must
+            // not have to walk the whole table on every subscribe to find out
+            // either (docs/process-lifecycle.md, "Who learns of a death").
+            _ = process.subscribeExits(endpoint);
+        }
+
+        /// Release everything task `dead` had subscribed. The slot owns the
+        /// endpoint capability, so reclaiming the slot closes it — otherwise a
+        /// process that subscribes and dies costs a handle-table slot that never
+        /// comes back.
+        pub fn forget(dead: u32) void {
+            for (&slots) |*slot| {
+                if (slot.used and slot.task == dead) {
+                    _ = ipc.close(slot.endpoint);
+                    slot.* = .{};
+                }
+            }
+        }
+
+        /// Whether `task` is a subscriber — the gate for an operation a provider
+        /// honours from its subscribers and nobody else. The power service's
+        /// shutdown is the one: the badge is kernel-stamped, so nothing in a
+        /// packet can claim to be the subscriber that already ran the stop
+        /// sequence.
+        pub fn has(task: u32) bool {
+            for (&slots) |*slot| {
+                if (slot.used and slot.task == task) return true;
+            }
+            return false;
+        }
+
+        /// Answer one received packet, with the reserved `subscribe` and
+        /// `unsubscribe` verbs already wired — a provider that leaves those two
+        /// handlers null (every provider should) gets the harness's. The turn's
+        /// capability is peeked, never taken, unless a slot actually kept it.
+        pub fn dispatch(
+            context: Context,
+            handlers: Handlers,
+            packet: []const u8,
+            sender: u32,
+            arrived: *ipc.Arrival,
+            reply: []u8,
+        ) usize {
+            var wired = handlers;
+            if (wired.subscribe == null) wired.subscribe = onSubscribe;
+            if (wired.unsubscribe == null) wired.unsubscribe = onUnsubscribe;
+            claimed = false;
+            const written = Provider.dispatch(context, wired, packet, sender, arrived.peek(), reply);
+            if (claimed) _ = arrived.take();
+            return written;
+        }
+
+        /// Push one event to every subscriber.
+        pub fn publish(
+            comptime event: Protocol.Event,
+            target: u64,
+            payload: Protocol.PayloadOf(event),
+        ) void {
+            publishClass(event, target, payload, every_event);
+        }
+
+        /// Push one event to the subscribers whose interest mask includes
+        /// `class` (a subscriber that named no class takes everything). The
+        /// packet is framed **once**, outside the loop, so every subscriber of a
+        /// class receives identical bytes; and delivery is `ipc.send`, which
+        /// never blocks, so one slow or dead subscriber can never stall the rest
+        /// — the whole reason broadcast is a provider pattern and not a kernel
+        /// primitive.
+        pub fn publishClass(
+            comptime event: Protocol.Event,
+            target: u64,
+            payload: Protocol.PayloadOf(event),
+            class: u32,
+        ) void {
+            var packet: [envelope.post_maximum]u8 = undefined;
+            const framed = Protocol.encodeEvent(event, target, payload, &packet) orelse return;
+            for (&slots) |*slot| {
+                if (!slot.used) continue;
+                if (!wants(slot.*, class)) continue;
+                // The sweep is what normally reclaims a dead subscriber, promptly
+                // and with its capability closed. This is the backstop for a
+                // notification that never arrived: an endpoint's notify ring is
+                // bounded, so a burst of deaths can drop one, and a send to an
+                // endpoint whose owner is gone fails rather than blocking.
+                if (!ipc.send(slot.endpoint, framed)) {
+                    _ = ipc.close(slot.endpoint);
+                    slot.* = .{};
+                }
+            }
+        }
+
+        fn wants(slot: Slot, class: u32) bool {
+            if (class == every_event) return true; // the event belongs to no class
+            if (slot.interest == every_event) return true; // the subscriber named none
+            return slot.interest & class != 0;
+        }
+
+        /// The reserved `subscribe` verb: register the caller's endpoint (the
+        /// call's capability) for the classes its tail names. A refusal simply
+        /// returns and the turn closes what arrived — the harness's ownership
+        /// rule (`ipc.Arrival`), which is why a subscribe storm against a full
+        /// table cannot spend the handle table.
+        fn onSubscribe(_: Context, invocation: envelope.Invocation(void), _: envelope.Answer(void)) isize {
+            const endpoint = invocation.capability orelse return -envelope.EPROTO; // no endpoint passed
+            const interest = envelope.decodeSubscribe(invocation.tail).interest;
+            for (&slots) |*slot| {
+                if (slot.used) continue;
+                // Appended, not replaced: one task may hold several subscriptions
+                // on different endpoints (a client taking keyboard and mouse as
+                // two streams), and each is its own conversation.
+                slot.* = .{ .used = true, .endpoint = endpoint, .task = invocation.sender, .interest = interest };
+                claimed = true; // the table holds it until that task dies
+                return 0;
+            }
+            return -envelope.ENOSPC; // table full
+        }
+
+        /// The reserved `unsubscribe` verb: every subscription the calling task
+        /// holds here goes, which is exactly what its death would do. It names no
+        /// endpoint because the badge already names the only subscriber a caller
+        /// can speak for — its own.
+        fn onUnsubscribe(_: Context, invocation: envelope.Invocation(void), _: envelope.Answer(void)) isize {
+            if (!has(invocation.sender)) return -envelope.ENOENT;
+            forget(invocation.sender);
+            return 0;
+        }
+    };
+}
+
+/// Run the service: create the endpoint, bind it under the service's contract
+/// name (if it has one), bind signals to it, call `init`, then serve until
+/// `terminate` arrives — at which point the loop returns and main's return is
+/// the clean exit the supervisor reads as `ExitReason.exited`.
+/// `maximum_message` sizes the receive and reply buffers (a service passes its
+/// protocol's message maximum).
 pub fn run(comptime maximum_message: usize, callbacks: Callbacks) void {
     const endpoint = ipc.createIpcEndpoint() orelse return;
-    if (callbacks.service) |id| {
+    if (callbacks.service) |name| {
-        if (!ipc.register(id, endpoint)) return;
+        if (!channel.bindPatiently(name, endpoint)) return;
     }
     _ = process.bindSignals(endpoint);
+    // Before `init`, so a subscriber that arrives the instant the name is bound
+    // is already covered by the sweep that will release it.
+    if (callbacks.subscribers) |subscribers| subscribers.watch(endpoint);
     if (callbacks.init) |initialise| {
         if (!initialise(endpoint)) return;
     }
@@ -59,6 +314,16 @@ pub fn run(comptime maximum_message: usize, callbacks: Callbacks) void {
     var receive: [maximum_message]u8 = undefined;
     while (true) {
         const got = ipc.replyWait(endpoint, reply_buffer[0..reply_len], &receive, null);
+        // Whatever capability came with this turn is the turn's, and the turn
+        // closes it unless a callback claims it (`ipc.Arrival`). Structural
+        // rather than a close per branch, because the branches are exactly what
+        // gets forgotten: the ping's `continue` below, and every `on_message`
+        // that has no use for a capability — which is every operation but a
+        // subscribe. A `defer` in a loop body runs on `continue` and on the
+        // `return` that ends the loop, so this covers all four exits.
+        var arrived: ipc.Arrival = .{ .handle = got.cap };
+        defer arrived.release();
+
         if (got.isNotification()) {
             reply_len = 0; // nothing owed for a notification
             if (process.signalsFrom(got.badge)) |signals| {
@@ -71,13 +336,20 @@ pub fn run(comptime maximum_message: usize, callbacks: Callbacks) void {
                 }
                 continue;
             }
+            // A death sweeps the subscriber table first, then still reaches the
+            // service: a provider often has its own per-client state to release
+            // (open file handles, device tokens, layers) and the same badge is
+            // the notice for both.
+            if (got.isChildExit()) {
+                if (callbacks.subscribers) |subscribers| subscribers.forget(got.childProcessId());
+            }
             if (callbacks.on_notification) |onNotification| onNotification(got.badge);
             continue;
         }
         if (got.len == 0) {
             reply_len = 0; // the universal ping: a zero-length reply, from the harness
-            continue;
+            continue; // any capability it carried goes out through the turn's `defer`
         }
-        reply_len = callbacks.on_message(receive[0..got.len], &reply_buffer, got.senderTaskId(), got.cap);
+        reply_len = callbacks.on_message(receive[0..got.len], &reply_buffer, got.senderTaskId(), &arrived);
     }
 }

library/protocol/block/block-protocol.zig

@@ -1,44 +1,61 @@
 //! The block-device wire protocol — what a filesystem (the FAT server) says to a
-//! block driver (usb-storage) over its well-known `.block` endpoint. A protocol
+//! block driver (usb-storage) over `/protocol/block`. Defined through the
-//! module like vfs-protocol / usb-transfer-protocol: extern-struct messages, an
+//! envelope, so every packet begins with the folded `Header`.
-//! `Operation` tag, everything in one IPC message.
+//!
+//! **`Header.target` is always 0 here**: a block driver instance serves exactly
+//! one device over its own endpoint, so there is no object within the peer to
+//! address. A driver that later fronts several volumes gives them target ids and
+//! `enumerate` lists them; nothing else about the protocol changes.
 //!
 //! Data path: read and write move whole blocks to or from a **caller-owned DMA
 //! buffer**, named by its physical address — the same physical-address handoff
 //! usb-storage already uses toward the controller, one layer up. So a 512-byte
-//! sector never has to cross the 256-byte IPC boundary; only the small request /
+//! sector never has to cross the packet floor; only the small request / reply
-//! reply headers do. (Safe while the IOMMU is unenforced; see docs/driver-model.md.)
+//! parts do. Under an enforcing IOMMU the buffer's physical addresses are only
+//! reachable by the device once the filesystem has `attach`ed the buffer's
+//! capability (the block server forwards it to the controller); see
+//! docs/driver-model.md.
 
-pub const Operation = enum(u32) {
+const envelope = @import("envelope");
-    /// geometry() -> { block_size, block_count }
+
-    geometry = 0,
+/// The answer to `geometry()`.
-    /// read(lba, count, physical): read `count` blocks from `lba` into the buffer
+pub const Geometry = extern struct {
-    read = 1,
+    block_size: u32, // bytes per block (512)
-    /// write(lba, count, physical): write `count` blocks at `lba` from the buffer
+    _padding: u32 = 0,
-    write = 2,
+    block_count: u64, // total blocks
-    /// flush(): commit any device write cache to stable media (no data transfer).
-    /// A filesystem calls this to make prior writes durable — e.g. before power-off,
-    /// so a shutdown-time write isn't lost in the USB flash controller's cache.
-    flush = 3,
 };
 
-pub const Request = extern struct {
+/// `read(lba, count, physical)` / `write(...)`: move `count` blocks between the
-    operation: u32,
+/// device and the caller's DMA buffer at `physical`.
-    reserved: u32 = 0,
+pub const Transfer = extern struct {
     lba: u64,
-    count: u32, // number of blocks (read/write)
+    count: u32,
-    reserved2: u32 = 0,
+    _padding: u32 = 0,
-    physical: u64, // caller's DMA buffer physical address (read/write)
+    physical: u64, // caller's DMA buffer physical address
 };
 
-pub const Reply = extern struct {
+/// How many blocks a transfer actually moved.
-    status: i32, // 0 on success, negative on failure
+pub const Transferred = extern struct { count: u32 };
-    reserved: u32 = 0,
-    block_size: u32, // geometry: bytes per block (512)
-    reserved2: u32 = 0,
-    block_count: u64, // geometry: total blocks; read/write: blocks moved
-};
 
-pub const message_maximum: usize = 256;
+pub const Protocol = envelope.Define(.{
-pub const request_size: usize = @sizeOf(Request);
+    .name = "block",
-pub const reply_size: usize = @sizeOf(Reply);
+    .version = 1,
+    .operations = &.{
+        .{ .name = "geometry", .reply = Geometry },
+        .{ .name = "read", .request = Transfer, .reply = Transferred },
+        .{ .name = "write", .request = Transfer, .reply = Transferred },
+        // flush(): commit any device write cache to stable media (no data
+        // transfer). A filesystem calls this to make prior writes durable —
+        // before power-off, so a shutdown-time write isn't lost in the USB flash
+        // controller's cache.
+        .{ .name = "flush" },
+        // attach(): the caller's DMA-region capability rides the call's cap
+        // slot; the block server forwards it to the controller so the buffer's
+        // physical addresses (named in later read/write) are reachable by the
+        // device under an enforcing IOMMU. Call once per buffer before using it.
+        .{ .name = "attach" },
+    },
+});
+
+pub const Operation = Protocol.Operation;
+pub const message_maximum: usize = Protocol.message_maximum;

library/protocol/build.zig

@@ -0,0 +1,74 @@
+//! The "protocol" library domain: the wire protocols — each service's public
+//! interface, exposed as its own module (docs/driver-model.md). Both sides of
+//! every conversation depend on the contract by name; neither reaches into the
+//! other's files. Pure flat wire types: no protocol module imports anything.
+//!
+//! One module here is not a protocol but the shape the others are written in,
+//! and therefore the one module every other one imports:
+//!
+//!   envelope                 : the packet prefix + comptime Define (docs/os-development/protocol-namespace.md)
+//!
+//!   vfs-protocol             : the VFS server <-> the file layer (unistd/stdio)
+//!   input-protocol           : the input fan-out service <-> sources + subscribers
+//!   block-protocol           : a filesystem <-> a block driver (usb-storage)
+//!   usb-transfer-protocol    : a USB class driver <-> the xHCI bus driver
+//!   device-manager-protocol  : the device manager <-> drivers + discovery
+//!   display-protocol         : the compositor's client-facing surface
+//!   scanout-protocol         : the compositor -> a native scanout driver (docs/display-v2.md)
+//!   power-protocol           : system power's domain-named surface (docs/power.md)
+
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    // Not a protocol, hence not `-protocol`: the envelope is what a protocol is
+    // defined *through*, so it is built first and handed to every protocol
+    // below as their one import.
+    const envelope = b.addModule("envelope", .{ .root_source_file = b.path("envelope/envelope.zig") });
+
+    for ([_]struct { name: []const u8, root: []const u8 }{
+        .{ .name = "vfs-protocol", .root = "vfs/vfs-protocol.zig" },
+        .{ .name = "input-protocol", .root = "input/input-protocol.zig" },
+        .{ .name = "block-protocol", .root = "block/block-protocol.zig" },
+        .{ .name = "usb-transfer-protocol", .root = "usb-transfer/usb-transfer-protocol.zig" },
+        .{ .name = "device-manager-protocol", .root = "device-manager/device-manager-protocol.zig" },
+        .{ .name = "display-protocol", .root = "display/display-protocol.zig" },
+        .{ .name = "scanout-protocol", .root = "scanout/scanout-protocol.zig" },
+        .{ .name = "power-protocol", .root = "power/power-protocol.zig" },
+    }) |protocol| {
+        _ = b.addModule(protocol.name, .{
+            .root_source_file = b.path(protocol.root),
+            .imports = &.{.{ .name = "envelope", .module = envelope }},
+        });
+    }
+
+    // Standalone `zig build test` for this domain alone; the root build keeps
+    // its aggregate test step.
+    const test_step = b.step("test", "Run the protocol unit tests");
+    // The envelope tests itself with no import of its own — everything else
+    // imports it, so it is built separately rather than importing itself.
+    const envelope_tests = b.addTest(.{
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("envelope/envelope.zig"), // framing round trips, verb numbering, dispatch, the floors
+            .target = b.resolveTargetQuery(.{}),
+        }),
+    });
+    test_step.dependOn(&b.addRunArtifact(envelope_tests).step);
+
+    for ([_][]const u8{
+        "vfs/vfs-protocol.zig", // NodeKind / DirectoryEntry sizes + op values
+        "input/input-protocol.zig", // event numbering + the push-floor budget
+        "display/display-protocol.zig", // pack(): native pixel encoding per format
+        "device-manager/device-manager-protocol.zig", // the dual-use report, exactly on the push floor
+        "power/power-protocol.zig", // the event kind as the packet's verb
+        "usb-transfer/usb-transfer-protocol.zig", // the tail-carried control stage + the trimmed report
+    }) |root| {
+        const protocol_tests = b.addTest(.{
+            .root_module = b.createModule(.{
+                .root_source_file = b.path(root),
+                .target = b.resolveTargetQuery(.{}),
+                .imports = &.{.{ .name = "envelope", .module = envelope }},
+            }),
+        });
+        test_step.dependOn(&b.addRunArtifact(protocol_tests).step);
+    }
+}

library/protocol/build.zig.zon

@@ -0,0 +1,8 @@
+.{
+    .name = .protocol,
+    .version = "0.0.0",
+    .fingerprint = 0xc8c0bc4c4d551283, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{},
+    .paths = .{""},
+}

library/protocol/device-manager/device-manager-protocol.zig

@@ -1,18 +1,51 @@
-//! The device-manager protocol (docs/device-manager.md): what drivers and
+//! The device-manager protocol (docs/device-driver-development/device-manager.md):
-//! applications say to the device manager over its well-known endpoint. The
+//! what drivers and applications say to the device manager over
-//! vfs-protocol pattern — extern-struct messages, a version in the handshake,
+//! `/protocol/device-manager`. Defined through the envelope
-//! reserved fields — so both sides depend on the contract by name. Deliberately
+//! (docs/os-development/protocol-namespace.md), so every packet — request, reply,
-//! contains nothing lifecycle-shaped: stopping, liveness (the zero-length ping),
+//! and pushed event alike — begins with the folded `Header`.
-//! and exit reasons are the universal vocabulary of
+//!
+//! **`Header.target` is the device id.** It was the `device_id` field of three
+//! different messages; folding it into the header is what made the packed
+//! leading operation byte disappear along with it. `no_device` addresses a
+//! driver that serves no enumerated device.
+//!
+//! Two of the manager's four old operations were the reserved verbs under
+//! another name and are gone from this protocol's own numbering: `enumerate`
+//! (the tree, one `ChildEntry` per record in the reply tail) and `subscribe`
+//! (the watcher's endpoint rides as the call's capability). What is left is the
+//! driver-facing half — the handshake and the two tree reports.
+//!
+//! **`ChildAdded` travels in both directions, and says so twice.** A bus driver
+//! *calls* `child_added` to report a device; the manager then *pushes* the same
+//! struct to every subscriber as the `child_added` event. Operations and events
+//! are numbered in separate spaces, so one struct under two numbers is exactly
+//! how the envelope spells "one encoding, both directions" — and the direction
+//! (call vs. send) already tells them apart.
+//!
+//! Deliberately contains nothing lifecycle-shaped: stopping, liveness (the
+//! zero-length ping), and exit reasons are the universal vocabulary of
 //! docs/process-lifecycle.md, not this protocol.
 
-/// The protocol version a driver states in its hello. A manager that cannot
+const std = @import("std");
-/// serve a driver's version refuses the hello, and the mismatch is loud at
+const envelope = @import("envelope");
-/// startup instead of quiet corruption later.
+
-pub const version: u16 = 1;
+/// The protocol version a driver states in its hello, and the version this
+/// contract answers `describe` with. A manager that cannot serve a driver's
+/// version refuses the hello, and the mismatch is loud at startup instead of
+/// quiet corruption later.
+///
+/// `describe` publishes the same number, but it cannot replace this: it tells a
+/// *client* what the provider is, and here it is the **provider** that has to
+/// learn what the client was built against in order to refuse it.
+pub const version = 1;
+
+/// `Header.target` for a driver that serves no enumerated device (a test
+/// fixture, a synthetic source), and `ChildAdded`'s answer for a leaf that was
+/// never `device_register`ed.
+pub const no_device: u64 = ~@as(u64, 0);
 
 /// Which bus a `child_added` came from — stated by the reporting bus driver so
-/// the manager's /etc/devices.csv matcher knows how to read the report's identity
+/// the manager's /system/configuration/devices.csv matcher knows how to read the report's identity
 /// (a PCI class triple vs a USB class triple are the same 24 bits but different
 /// namespaces) and which `bus` column a rule must name to bind it. `unknown` is
 /// the zero default, so an un-upgraded reporter fails to match rather than
@@ -24,7 +57,7 @@ pub const BusKind = enum(u8) {
     acpi = 3,
 };
 
-/// What kind of driver is talking (docs/driver-model.md's shapes).
+/// What kind of driver is talking (docs/device-driver-development/driver-model.md's shapes).
 pub const Role = enum(u8) {
     /// Owns a controller and reports the devices behind it (`child_added`).
     bus = 1,
@@ -32,58 +65,45 @@ pub const Role = enum(u8) {
     device = 2,
 };
 
-/// The message kinds.
+// --- the per-operation request parts ----------------------------------------
-pub const Operation = enum(u8) {
+//
-    hello = 1,
+// Each names the bytes AFTER the prefix. Nothing here carries an operation or a
-    child_added = 2,
+// device id: those are the packet header's, folded in once. No reply part
-    child_removed = 3,
+// carries a status either — that is the `Status` every reply already begins
-    enumerate = 4,
+// with, so the manager's old three `{status, reserved}` reply structs are gone.
-    subscribe = 5,
-};
-
-/// `Hello.device_id` for a driver that serves no enumerated device (a test
-/// fixture, a synthetic source).
-pub const no_device: u64 = ~@as(u64, 0);
 
 /// The handshake, sent once by every driver the manager spawns — the manager's
 /// one self-enforced deadline: spawned and silent past it means wrong binary,
-/// wrong version, or wedged before main, and the stop sequence follows.
+/// wrong version, or wedged before main, and the stop sequence follows. The
+/// device this driver was assigned (its argv[1]) is `Header.target`.
 pub const Hello = extern struct {
-    operation: u8 = @intFromEnum(Operation.hello),
+    /// A `Role` value.
-    /// A Role value.
     role: u8,
+    _padding: u8 = 0,
     /// The protocol version this driver was built against (`version`).
     version: u16 = version,
-    reserved: u32 = 0,
-    /// The device this driver was assigned (its argv[1]), or `no_device`.
-    device_id: u64,
 };
 
-pub const hello_size = @sizeOf(Hello);
-
-/// The manager's answer to a hello. Nonzero status = refused (version mismatch,
-/// unknown sender); a refused driver should exit cleanly.
-pub const HelloReply = extern struct {
-    status: i32,
-    reserved: u32 = 0,
-};
-
-pub const reply_size = @sizeOf(HelloReply);
-
 /// A bus driver reporting one device it discovered behind its controller
-/// (docs/device-manager.md "the tree"). Identity is the bus's native language —
+/// (docs/device-driver-development/device-manager.md "the tree"), and the payload
-/// for USB a port-speed class; the (class, subclass, protocol) triple joins it
+/// the manager pushes to its subscribers for the same event. Identity is the
-/// once control transfers exist (the USB track). The manager mirrors the child
+/// bus's native language — for USB a port-speed class, for PCI the class triple.
-/// into its tree; when the reporting driver dies, the manager prunes everything
+/// The manager mirrors the child into its tree; when the reporting driver dies,
-/// it reported (the children describe protocol state that died with it) and the
+/// the manager prunes everything it reported (the children describe protocol
-/// restarted instance rediscovers and re-reports.
+/// state that died with it) and the restarted instance rediscovers and
+/// re-reports.
+///
+/// `Header.target` is the kernel device id this child was `device_register`ed
+/// as — what the manager hands a matched driver as its argv assignment — or
+/// `no_device` for an unregistered leaf (a USB port before the descriptor
+/// track). That is the field that used to sit at the end of this struct.
+///
+/// **The field order is the size budget.** An event packet is the header plus
+/// this, within 64 bytes, and three `u64`s round the whole struct up to a
+/// multiple of eight whatever order they sit in — so the small fields are
+/// packed tail-first into the space the rounding pays for anyway. `Define`
+/// checks the result; this comment is why there is no slack in it.
 pub const ChildAdded = extern struct {
-    operation: u8 = @intFromEnum(Operation.child_added),
-    /// A `BusKind` value: which bus reported this child, so the manager reads the
-    /// identity in the right namespace and matches against the right `bus` column.
-    bus: u8 = @intFromEnum(BusKind.unknown),
-    reserved1: u16 = 0,
-    reserved2: u32 = 0,
     /// The reporting driver's own device (the controller) — the child's parent.
     parent: u64,
     /// Where on the bus (for USB: the root port number, 1-based).
@@ -91,85 +111,130 @@ pub const ChildAdded = extern struct {
     /// Bus-specific identity (for USB: the PORTSC port-speed class; for PCI:
     /// the class triple; for ACPI devices, 0 — identity is the hid below).
     identity: u64,
-    /// The kernel device id this child was `device_register`ed as — what the
+    /// The PCI subsystem id, packed `(subsystem_vendor << 16) | subsystem_device`
-    /// manager hands a matched driver as its argv assignment — or `no_device`
+    /// (so it reads vendor-first, matching the CSV's `ssvid:ssid`), or 0 when the
-    /// for an unregistered leaf (a USB port before the descriptor track).
+    /// device has no subsystem id (a bridge, or a non-PCI bus).
-    device_id: u64 = no_device,
+    subsystem: u32 = 0,
     /// The vendor id (PCI vendor / USB idVendor), or 0 when the bus has no such
-    /// concept (ACPI). Carried so the manager's /etc/devices.csv matcher can bind
+    /// concept (ACPI). Carried so the manager's /system/configuration/devices.csv matcher can bind
     /// on vendor — a level the bus-native `identity` (a class triple) cannot express.
     vendor: u16 = 0,
     /// The device id (PCI device / USB idProduct), or 0. The most specific numeric
     /// level: this is what lets one virtio-gpu (1AF4:1050) be told from any other
     /// virtio display function without the driver re-confirming after it is spawned.
     device: u16 = 0,
-    /// The PCI subsystem id, packed `(subsystem_vendor << 16) | subsystem_device`
-    /// (so it reads vendor-first, matching the CSV's `ssvid:ssid`), or 0 when the
-    /// device has no subsystem id (a bridge, or a non-PCI bus).
-    subsystem: u32 = 0,
     /// The ACPI hardware id (`_HID`), EISA-decoded (e.g. "PNP0303"), for devices
     /// discovered by firmware string rather than a numeric bus identity. Empty
     /// (all zero) otherwise. Widens for FDT `compatible` strings later.
     hid: [8]u8 = .{0} ** 8,
+    /// A `BusKind` value: which bus reported this child, so the manager reads the
+    /// identity in the right namespace and matches against the right `bus` column.
+    bus: u8 = @intFromEnum(BusKind.unknown),
+    _padding: [7]u8 = .{0} ** 7,
 };
 
-pub const child_added_size = @sizeOf(ChildAdded);
+/// A bus driver reporting a device gone (hot-unplug), and the payload pushed to
-
+/// subscribers for it.
-/// A bus driver reporting a device gone (hot-unplug). Not yet sent by any
+///
-/// driver — the port scan has no unplug interrupt — but the manager handles it;
+/// **This is the one message whose target stays 0.** A removal is addressed by
-/// death-pruning covers removal until hotplug lands.
+/// the composite (parent, bus address) — the reporter knows where the device
+/// *was*, not necessarily what id it had been registered under — and a single
+/// `u64` cannot carry a pair. So the address stays in the payload, where it
+/// always was, and the header addresses the provider itself.
 pub const ChildRemoved = extern struct {
-    operation: u8 = @intFromEnum(Operation.child_removed),
-    reserved0: u8 = 0,
-    reserved1: u16 = 0,
-    reserved2: u32 = 0,
     parent: u64,
     bus_address: u64,
 };
 
-pub const child_removed_size = @sizeOf(ChildRemoved);
+/// One record of the reserved `enumerate` reply: the manager's mirror, one
-
+/// entry per known child, packed into the reply tail. The count is
-/// The manager's answer to a tree report.
+/// `Status.len / @sizeOf(ChildEntry)` — the envelope's reply length says how
-pub const ReportReply = extern struct {
+/// many arrived, so no count header is spent on saying it twice.
-    status: i32,
-    reserved: u32 = 0,
-};
-
-/// An application asking for the tree (M18.3): the reply is an EnumerateReply
-/// header followed by `count` ChildEntry records.
-pub const Enumerate = extern struct {
-    operation: u8 = @intFromEnum(Operation.enumerate),
-    reserved0: u8 = 0,
-    reserved1: u16 = 0,
-    reserved2: u32 = 0,
-};
-
-pub const EnumerateReply = extern struct {
-    status: i32,
-    /// ChildEntry records following this header.
-    count: u32,
-};
-
 pub const ChildEntry = extern struct {
     parent: u64,
     bus_address: u64,
     identity: u64,
 };
 
-/// An application subscribing to published add/remove events (the input-service
+/// How many `ChildEntry` records one `enumerate` reply can carry. Paging joins
-/// pattern): the subscriber's endpoint rides as the call's **capability**, and
+/// the protocol if a tree ever outgrows one packet.
-/// events arrive on it as buffered messages whose payload is the same
+pub const entries_per_reply: usize = (envelope.packet_maximum - envelope.prefix_size) / @sizeOf(ChildEntry);
-/// ChildAdded / ChildRemoved struct the bus drivers send — one encoding, both
-/// directions.
-pub const Subscribe = extern struct {
-    operation: u8 = @intFromEnum(Operation.subscribe),
-    reserved0: u8 = 0,
-    reserved1: u16 = 0,
-    reserved2: u32 = 0,
-};
 
-/// Upper bound on any message in this protocol — sizes the endpoint buffers.
+pub const Protocol = envelope.Define(.{
-/// Capped by the kernel's IPC MESSAGE_MAXIMUM (256): an EnumerateReply carries
+    .name = "device-manager",
-/// up to ten ChildEntry records per call, plenty for the mirror's current
+    .version = version,
-/// bounds; paging joins the protocol if a tree ever outgrows one message.
+    .operations = &.{
-pub const message_maximum = 256;
+        // The driver-facing half. `enumerate` and `subscribe` are not here: they
+        // are the reserved verbs, which mean the same thing at every provider.
+        .{ .name = "hello", .request = Hello },
+        .{ .name = "child_added", .request = ChildAdded },
+        .{ .name = "child_removed", .request = ChildRemoved },
+    },
+    .events = &.{
+        // The watcher-facing half — the same two structs, pushed rather than
+        // called, in the events' own numbering space.
+        .{ .name = "child_added", .payload = ChildAdded },
+        .{ .name = "child_removed", .payload = ChildRemoved },
+    },
+});
+
+pub const Operation = Protocol.Operation;
+pub const Event = Protocol.Event;
+
+/// What the manager sizes its buffers to — the call floor, as every protocol does.
+pub const message_maximum: usize = Protocol.message_maximum;
+
+test "a tree report fits the push floor with the header folded in" {
+    // The dual-use struct is the tight one: `child_added` is both a call and an
+    // event, and the event floor is 64 bytes *including* the header. Forty-one
+    // bytes of content, rounded to 48 by the three u64s' alignment, plus the
+    // 16-byte header — exactly on the floor, which is what folding the operation
+    // byte and the device id out of the payload bought.
+    try std.testing.expectEqual(@as(usize, 48), @sizeOf(ChildAdded));
+    try std.testing.expectEqual(envelope.post_maximum, Protocol.event_maximum);
+    try std.testing.expect(Protocol.event_maximum <= envelope.post_maximum);
+    // Ten records per enumerate reply — what the old count-header layout carried.
+    try std.testing.expectEqual(@as(usize, 10), entries_per_reply);
+}
+
+test "the verb and event numbering, and the device id in the header" {
+    try std.testing.expectEqual(@as(u32, 16), @intFromEnum(Operation.hello));
+    try std.testing.expectEqual(@as(u32, 17), @intFromEnum(Operation.child_added));
+    try std.testing.expectEqual(@as(u32, 18), @intFromEnum(Operation.child_removed));
+    // Events number in their own space, so the same two reports start at 16 too.
+    try std.testing.expectEqual(@as(u32, 16), @intFromEnum(Event.child_added));
+    try std.testing.expectEqual(@as(u32, 17), @intFromEnum(Event.child_removed));
+    // The manager's own enumerate/subscribe became the RESERVED verbs, below the
+    // protocol range entirely.
+    try std.testing.expectEqual(@as(u32, 1), envelope.operation_enumerate);
+    try std.testing.expectEqual(@as(u32, 2), envelope.operation_subscribe);
+
+    var buffer: [message_maximum]u8 = undefined;
+    const hello = Protocol.encodeRequest(.hello, 7, .{ .role = @intFromEnum(Role.bus) }, &.{}, &buffer).?;
+    try std.testing.expectEqual(@as(u64, 7), envelope.headerOf(hello).?.target);
+    try std.testing.expectEqual(@as(u16, 1), Protocol.decodeRequest(.hello, hello).?.version);
+}
+
+test "one struct, two numbers: the report a bus calls and the event a watcher is pushed" {
+    const report = ChildAdded{
+        .parent = 3,
+        .bus_address = 1,
+        .identity = 0x030000,
+        .bus = @intFromEnum(BusKind.pci),
+        .vendor = 0x1AF4,
+    };
+
+    var call: [message_maximum]u8 = undefined;
+    const called = Protocol.encodeRequest(.child_added, 42, report, &.{}, &call).?;
+    try std.testing.expectEqual(Operation.child_added, Protocol.operationOf(called).?);
+    try std.testing.expectEqual(@as(u64, 42), envelope.headerOf(called).?.target);
+
+    var push: [envelope.post_maximum]u8 = undefined;
+    const pushed = Protocol.encodeEvent(.child_added, 42, report, &push).?;
+    try std.testing.expectEqual(envelope.post_maximum, pushed.len);
+    try std.testing.expectEqual(Event.child_added, Protocol.eventOf(pushed).?);
+    try std.testing.expectEqual(@as(u16, 0x1AF4), Protocol.decodeEvent(.child_added, pushed).?.vendor);
+    // Same bytes after the prefix, different verb in it — the direction is what
+    // tells a call from a push, and the numbering spaces never collide.
+    try std.testing.expectEqualSlices(u8, called[envelope.prefix_size..], pushed[envelope.prefix_size..]);
+}

library/protocol/display/display-protocol.zig

@@ -1,93 +1,137 @@
-//! The display wire protocol — what a client says to the display service over its
+//! The display wire protocol — what a client says to the display service over
-//! well-known `.display` endpoint. extern-struct messages with an `Operation` tag, the
+//! `/protocol/display`. The compositor owns the framebuffer and an ordered stack of
-//! same shape as block/vfs/input protocols. The compositor owns the framebuffer and an
+//! **layers**; a client creates layers, draws into them with these operations, marks damage,
-//! ordered stack of **layers**; a client creates layers, draws into them with these
+//! and asks for a `present`. v1 surfaces are server-owned (a client draws by command);
-//! operations, marks damage, and asks for a `present`. v1 surfaces are server-owned (a
+//! shared-memory surfaces are a later milestone (docs/display.md).
-//! client draws by command); shared-memory surfaces are a later milestone (docs/display.md).
+//!
+//! **`Header.target` is the layer** on every verb that names one — the field that used to be
+//! `Request.layer`. `info`, `present`, `set_mode`, `get_modes` and `attach_scanout` address
+//! the compositor itself, so they leave it 0.
+//!
+//! Every verb carries its own request type. The single overloaded 40-byte request this
+//! protocol used to have is gone, and with it the field abuse it invited: `attach_scanout`
+//! spent `x` on a stride, `y` on a refresh rate and `colour` on a pixel format, which no
+//! reader could have guessed and no compiler could have caught.
 
+const envelope = @import("envelope");
 const std = @import("std");
 
-pub const Operation = enum(u32) {
+/// The answer to `info()`: the display's current mode.
-    /// info() -> { width, height, pitch, format }: the display's current mode.
+pub const Info = extern struct {
-    info = 0,
-    /// create_layer(x, y, width, height, z) -> { layer }: a new server-owned surface.
-    create_layer = 1,
-    /// configure_layer(layer, x, y, z, visible): move, restack, show, or hide a layer.
-    configure_layer = 2,
-    /// destroy_layer(layer): release a layer.
-    destroy_layer = 3,
-    /// fill_rect(layer, x, y, width, height, colour): fill a rectangle of a layer.
-    fill_rect = 4,
-    /// blit_tile(layer, x, y, width, height, <inline pixels>): copy a small pixel tile in.
-    blit_tile = 5,
-    /// damage(layer, x, y, width, height): mark a region dirty for the next present.
-    damage = 6,
-    /// present(): composite the dirty layers and flush to the screen.
-    present = 7,
-    /// attach_scanout(x=stride, y=refresh_hz, width, height, colour=format) + <surface
-    /// capability>: a native scanout driver announces itself, handing over the shared scanout
-    /// surface as an `ipc_call` send_cap. The compositor maps it, looks up the driver's
-    /// `.scanout` present channel, and upgrades off the GOP floor (docs/display-v2.md V4).
-    /// `x` is the surface's row stride in pixels, `y` the panel refresh rate from the
-    /// driver's EDID read (0 = unknown; paces the compositor's frame clock), `colour` the
-    /// DisplayFormat.
-    attach_scanout = 8,
-    /// set_mode(width, height): change the display resolution — only a native backend that
-    /// reports `canModeSet` honours it; on the GOP floor it fails (docs/display-v2.md V5).
-    set_mode = 9,
-    /// get_modes() -> ModesReply: the resolutions the display can switch to (empty on GOP).
-    get_modes = 10,
-};
-
-/// The fixed request header. A `blit_tile`'s pixel payload (width*height 32-bit pixels)
-/// follows this header inline in the same message, up to `maximum_payload`.
-pub const Request = extern struct {
-    operation: u32,
-    layer: u32 = 0, // create/configure/destroy/fill/blit/damage: the target layer
-    x: u32 = 0,
-    y: u32 = 0,
     width: u32 = 0,
     height: u32 = 0,
-    z: u32 = 0, // create_layer / configure_layer: stacking order (higher = in front)
+    pitch: u32 = 0, // bytes per row (may exceed width*4)
-    colour: u32 = 0, // fill_rect: the fill colour (native pixel value)
-    visible: u32 = 1, // configure_layer: 0 hides the layer
-    reserved: u32 = 0,
-};
-
-pub const Reply = extern struct {
-    status: i32, // 0 on success, negative on failure
-    reserved: u32 = 0,
-    // info():
-    width: u32 = 0,
-    height: u32 = 0,
-    pitch: u32 = 0,
     format: u32 = 0, // a device-abi DisplayFormat value (0 = rgbx, 1 = bgrx)
-    // create_layer():
-    layer: u32 = 0,
-    reserved2: u32 = 0,
 };
 
+/// `create_layer(...)`: a new server-owned surface. Coordinates are signed — a layer may sit
+/// partly off-screen.
+pub const CreateLayer = extern struct {
+    x: i32,
+    y: i32,
+    width: u32,
+    height: u32,
+    z: u32 = 0, // stacking order (higher = nearer the front)
+    visible: u32 = 1,
+};
+
+/// The layer a `create_layer` established — the integer later packets put in `Header.target`.
+pub const Created = extern struct { layer: u32 };
+
+/// `configure_layer(...)` on `Header.target`: move, restack, show, or hide it.
+pub const ConfigureLayer = extern struct {
+    x: i32,
+    y: i32,
+    z: u32 = 0,
+    visible: u32 = 1, // 0 hides the layer
+};
+
+/// `fill_rect(...)` on `Header.target`: fill a layer-local rectangle with a native pixel value.
+pub const FillRect = extern struct {
+    x: i32,
+    y: i32,
+    width: u32,
+    height: u32,
+    colour: u32,
+};
+
+/// `blit_tile(...)` on `Header.target`: copy a `width`×`height` tile of native pixels
+/// (row-major, little-endian) into the layer. The pixels ride inline as the packet's tail,
+/// up to `maximum_payload`.
+pub const BlitTile = extern struct {
+    x: i32,
+    y: i32,
+    width: u32,
+    height: u32,
+};
+
+/// `damage(...)` on `Header.target`: mark a layer-local region dirty for the next present.
+pub const Damage = extern struct {
+    x: i32,
+    y: i32,
+    width: u32,
+    height: u32,
+};
+
+/// `attach_scanout(...)` + the shared surface as the call's capability: a native scanout
+/// driver announces itself. The compositor maps the surface, opens the driver's
+/// `/protocol/scanout` present channel, and upgrades off the GOP floor (docs/display-v2.md
+/// V4). Each field says what it is, which the old shared request could not.
+pub const AttachScanout = extern struct {
+    /// The surface's row stride in pixels (it is sized to the driver's largest mode).
+    stride: u32,
+    /// The active mode within that surface.
+    width: u32,
+    height: u32,
+    /// A device-abi DisplayFormat value.
+    format: u32,
+    /// The panel refresh rate from the driver's EDID read (0 = unknown); it paces the
+    /// compositor's frame clock.
+    refresh_hz: u32 = 0,
+};
+
+/// `set_mode(width, height)`: change the display resolution — only a native backend that
+/// reports `canModeSet` honours it; on the GOP floor it fails (docs/display-v2.md V5).
+pub const SetMode = extern struct { width: u32, height: u32 };
+
 /// One selectable display mode.
 pub const Mode = extern struct { width: u32, height: u32 };
 pub const max_modes = 4;
 
-/// The reply to `get_modes`: a small fixed list of resolutions the display can switch to.
+/// The answer to `get_modes`: the resolutions the display can switch to (empty on GOP).
-pub const ModesReply = extern struct {
+pub const Modes = extern struct {
-    status: i32,
+    count: u32 = 0,
-    count: u32,
+    _padding: u32 = 0,
-    modes: [max_modes]Mode,
+    modes: [max_modes]Mode = @splat(.{ .width = 0, .height = 0 }),
 };
-pub const modes_reply_size: usize = @sizeOf(ModesReply);
 
-/// The IPC message size — the kernel caps every message at `MESSAGE_MAXIMUM` (256 bytes,
+pub const Protocol = envelope.Define(.{
-/// system/kernel/ipc-synchronous.zig), so this matches it (a larger receive/reply buffer
+    .name = "display",
-/// is rejected with -E2BIG). A `blit_tile` therefore carries only a *small* tile inline —
+    .version = 1,
-/// `maximum_payload` bytes = up to 54 pixels, enough for a cursor or small sprite; larger
+    .operations = &.{
-/// bitmaps are the deferred shared-memory surface path (docs/display.md).
+        .{ .name = "info", .reply = Info },
-pub const message_maximum: usize = 256;
+        .{ .name = "create_layer", .request = CreateLayer, .reply = Created },
-pub const request_size: usize = @sizeOf(Request);
+        .{ .name = "configure_layer", .request = ConfigureLayer },
-pub const reply_size: usize = @sizeOf(Reply);
+        .{ .name = "destroy_layer" },
-pub const maximum_payload: usize = message_maximum - request_size;
+        .{ .name = "fill_rect", .request = FillRect },
+        .{ .name = "blit_tile", .request = BlitTile },
+        .{ .name = "damage", .request = Damage },
+        .{ .name = "present" },
+        .{ .name = "attach_scanout", .request = AttachScanout },
+        .{ .name = "set_mode", .request = SetMode },
+        .{ .name = "get_modes", .reply = Modes },
+    },
+});
+
+pub const Operation = Protocol.Operation;
+pub const message_maximum: usize = Protocol.message_maximum;
+
+/// The largest inline pixel tile a `blit_tile` may carry: the call floor less the header and
+/// this verb's own fixed part — 224 bytes, up to 56 pixels, enough for a cursor or a small
+/// sprite. Larger bitmaps are the deferred shared-memory surface path (docs/display.md).
+/// Per-verb rather than protocol-wide, because with per-operation requests there is no
+/// single "request size" to subtract any more.
+pub const maximum_payload: usize = envelope.packet_maximum - envelope.prefix_size - @sizeOf(BlitTile);
 
 /// Pack an 8-bit-per-channel colour into the display's native 32-bit pixel for `format`
 /// (a device-abi `DisplayFormat`: 0 = rgbx, 1 = bgrx). Shared so a `colour` in a
@@ -113,3 +157,15 @@ test "pack encodes native byte order for rgbx and bgrx" {
     try std.testing.expectEqual(@as(u32, 0x00AA_0000), pack(1, 0xAA, 0, 0));
     try std.testing.expectEqual(@as(u32, 0x0000_3020), pack(0, 0x20, 0x30, 0)); // green in byte 1
 }
+
+test "the layer rides the header, and the blit tile grew with the split" {
+    var buffer: [message_maximum]u8 = undefined;
+    const pixels = [_]u8{0xFF} ** 16;
+    const packet = Protocol.encodeRequest(.blit_tile, 3, .{ .x = 1, .y = 2, .width = 2, .height = 2 }, &pixels, &buffer).?;
+    try std.testing.expectEqual(@as(u64, 3), envelope.headerOf(packet).?.target);
+    try std.testing.expectEqual(@as(i32, 1), Protocol.decodeRequest(.blit_tile, packet).?.x);
+    try std.testing.expectEqual(@as(usize, 16), Protocol.requestTail(.blit_tile, packet).len);
+    // 216 bytes under the old 40-byte shared request; the header plus this
+    // verb's own four fields is 32.
+    try std.testing.expectEqual(@as(usize, 224), maximum_payload);
+}

library/protocol/envelope/envelope.zig

@@ -0,0 +1,974 @@
+//! The envelope — the fixed prefix every danos packet begins with, and the
+//! comptime `Define` that builds a protocol out of it. Layer L2 of
+//! [communication.md](../../../docs/os-development/communication.md); the
+//! authoritative description is
+//! [protocol-namespace.md](../../../docs/os-development/protocol-namespace.md).
+//!
+//! This is the one module in the protocol domain that is not itself a protocol:
+//! it is the shape every protocol is expressed in. A protocol module hands
+//! `Define` its verbs and events and gets back numbered operations (never
+//! colliding with the reserved range), typed encode/decode helpers, a
+//! provider-side dispatch table that answers `describe` on its own — and, the
+//! point of the exercise, compile-time proof that none of its packets can
+//! exceed the transport floor. Errors that used to surface as runtime
+//! truncation are compile errors, and "packets never fragment" is enforced at
+//! the source rather than by review.
+//!
+//! **The prefix is folded, never stacked.** A `request`, `reply`, or `payload`
+//! type names the bytes that follow the prefix — never the whole packet. The
+//! verb and the object being addressed live in the prefix, so a protocol type
+//! carries neither an `operation` field of its own nor a nested `Header`;
+//! `rejectStacking` refuses one at compile time, and every size check adds
+//! `prefix_size` exactly once.
+
+const std = @import("std");
+
+// --- the prefix -------------------------------------------------------------
+
+/// Every packet a danos protocol transmits begins with this header — requests
+/// on the synchronous call path, event packets on the asynchronous push path.
+/// A reply spends the same 16 bytes on `Status` instead.
+pub const Header = extern struct {
+    /// The verb. Values below `first_protocol_operation` are the reserved
+    /// universal verbs, which mean the same thing in every protocol.
+    operation: u32,
+    _padding: u32 = 0,
+    /// **Object** addressing within the peer, never party addressing: which of
+    /// the peer's objects this packet operates on — a volume, a layer, a node,
+    /// a device. `0` addresses the provider itself, and a protocol with no
+    /// objects never uses the field. *Which* party is at the other end was
+    /// decided once, when the channel was opened, and *who sent this* is the
+    /// kernel-stamped badge; neither is ever written here, which is what keeps
+    /// the source unforgeable.
+    target: u64 = 0,
+};
+
+/// Every reply begins with this. `len` counts the bytes that follow: the
+/// reply's fixed part plus whatever variable tail the operation defines.
+pub const Status = extern struct {
+    status: i32, // 0, or a negative errno
+    _padding: u32 = 0,
+    len: u32 = 0,
+    _padding2: u32 = 0,
+};
+
+/// The fixed prefix every packet spends — `Header` on a request or an event,
+/// `Status` on a reply. One constant, because the two are deliberately the same
+/// width: the packet budget does not depend on the direction.
+pub const prefix_size: usize = @sizeOf(Header);
+
+comptime {
+    if (@sizeOf(Header) != 16 or @sizeOf(Status) != 16)
+        @compileError("the envelope prefix is 16 bytes in both directions");
+}
+
+// --- the reserved verbs -----------------------------------------------------
+
+/// Reserved verbs, answered by every provider. `Define` numbers a protocol's
+/// own verbs from `first_protocol_operation`, so no protocol can reach in here.
+pub const operation_describe: u32 = 0; // -> protocol name, version, target kinds
+pub const operation_enumerate: u32 = 1; // -> the current targets, one per reply page
+pub const operation_subscribe: u32 = 2; // capability = the subscriber's endpoint
+pub const operation_unsubscribe: u32 = 3;
+pub const first_protocol_operation: u32 = 16;
+
+/// The optional body of a reserved `subscribe`: **which** of a provider's events
+/// the subscriber wants, as a bit mask whose meaning the protocol defines (the
+/// input service's device classes are the model). A reserved verb carries no
+/// typed request, so this rides the packet's tail — and zero, which is also what
+/// a subscribe that sent no body at all reads as, means *every* event.
+///
+/// The mask lives here rather than in each protocol because the subscriber
+/// machinery is the service harness's (library/kernel/service.zig): the harness
+/// records the number, the protocol decides what its bits mean, and neither has
+/// to know the other.
+pub const Subscription = extern struct { interest: u32 = 0 };
+
+/// Frame a `subscribe` request. The subscriber's own endpoint travels as the
+/// call's *capability*, never in the packet — that is what makes the reverse
+/// path unforgeable.
+pub fn encodeSubscribe(interest: u32, buffer: []u8) ?[]u8 {
+    const header = Header{ .operation = operation_subscribe };
+    const body = Subscription{ .interest = interest };
+    return frame(std.mem.asBytes(&header), std.mem.asBytes(&body), &.{}, buffer);
+}
+
+/// Frame a bare `unsubscribe`: it names no event and no endpoint, because it
+/// means "every subscription this task holds here" (one task, one voice).
+pub fn encodeUnsubscribe(buffer: []u8) ?[]u8 {
+    const header = Header{ .operation = operation_unsubscribe };
+    return frame(std.mem.asBytes(&header), &.{}, &.{}, buffer);
+}
+
+/// The interest mask out of a `subscribe` packet's tail, on the provider's side.
+/// A caller that sent no mask reads as the every-event mask.
+pub fn decodeSubscribe(tail: []const u8) Subscription {
+    if (tail.len < @sizeOf(Subscription)) return .{};
+    return std.mem.bytesToValue(Subscription, tail[0..@sizeOf(Subscription)]);
+}
+
+/// The `describe` reply's fixed part, followed inline by `name_len` bytes of the
+/// protocol's name. This is the version handshake: the version is asked for
+/// once, at connect time, rather than re-carried by every packet out of a
+/// 256-byte budget.
+pub const Description = extern struct {
+    version: u32,
+    operation_count: u32,
+    event_count: u32,
+    name_len: u32,
+};
+
+/// Longest protocol name a `describe` reply can carry.
+pub const name_maximum: usize = packet_maximum - prefix_size - @sizeOf(Description);
+
+// --- the transport floor ----------------------------------------------------
+
+/// The packet budget every protocol may assume on *any* transport. These are
+/// the kernel-ipc transport's limits — `MESSAGE_MAXIMUM` and `POST_MAXIMUM` in
+/// system/kernel/ipc-synchronous.zig — restated here because the kernel keeps
+/// them private and a protocol has to compile against something. A fatter
+/// transport raises its own ceiling; the floor does not move, so a protocol
+/// that fits here fits everywhere (communication.md: ceilings are transport
+/// properties, the floor is the protocol's contract).
+pub const packet_maximum: usize = 256; // one request or one reply (ipc_call)
+pub const post_maximum: usize = 64; // one event packet (ipc_send)
+
+/// Whether a request or reply whose fixed part is `T` fits the call floor once
+/// the prefix is counted. The folded rule in one line: `prefix_size` is added
+/// exactly once, because `T` describes only what follows it. Exported so the
+/// rule itself is testable — `Define` enforces it as a compile error.
+pub fn fitsPacket(comptime T: type) bool {
+    return prefix_size + @sizeOf(T) <= packet_maximum;
+}
+
+/// The same, against the much smaller push floor an event packet lives within.
+pub fn fitsPost(comptime T: type) bool {
+    return prefix_size + @sizeOf(T) <= post_maximum;
+}
+
+// --- reply statuses the envelope itself produces -----------------------------
+
+/// Continued from the kernel's danos-native errno numbering
+/// (system/kernel/ipc-synchronous.zig, which ends at `EPERM` = 9), so a client
+/// reads one vocabulary whether the number came from the kernel or a provider.
+/// Positive here, sent negated in `Status.status`, as the kernel spells it.
+pub const ENOSYS: i32 = 10; // this protocol has no such operation
+pub const EPROTO: i32 = 11; // malformed packet: shorter than the verb it names
+pub const EBUSY: i32 = 12; // the thing asked for is held by someone still alive
+
+/// Restated from the kernel's half of the numbering, because a provider refuses
+/// too and userspace has no other place to read these from: `ENOENT` is "no such
+/// name", `EPERM` "not permitted". The protocol registry answers an ungranted
+/// bind with the second and a name a live provider already holds with `EBUSY`.
+pub const ENOENT: i32 = 4;
+pub const ENOSPC: i32 = 5;
+pub const EPERM: i32 = 9;
+
+// --- framing ----------------------------------------------------------------
+
+/// The header of a received packet, or null when it is too short to have one.
+pub fn headerOf(packet: []const u8) ?Header {
+    if (packet.len < prefix_size) return null;
+    return std.mem.bytesToValue(Header, packet[0..prefix_size]);
+}
+
+/// The status of a received reply, or null when it is too short to have one.
+pub fn statusOf(packet: []const u8) ?Status {
+    if (packet.len < prefix_size) return null;
+    return std.mem.bytesToValue(Status, packet[0..prefix_size]);
+}
+
+/// Frame a bare `describe` request. Protocol-independent: the reserved verbs
+/// are asked the same way of every provider.
+pub fn encodeDescribe(buffer: []u8) ?[]u8 {
+    const header = Header{ .operation = operation_describe };
+    return frame(std.mem.asBytes(&header), &.{}, &.{}, buffer);
+}
+
+/// A decoded `describe` reply: the fixed part, plus the name that follows it.
+pub const Described = struct {
+    description: Description,
+    name: []const u8,
+};
+
+/// Decode a `describe` reply packet. Null if it failed, was truncated, or is
+/// not a description at all.
+pub fn decodeDescribe(packet: []const u8) ?Described {
+    const status = statusOf(packet) orelse return null;
+    if (status.status != 0) return null;
+    const body = packet[prefix_size..];
+    if (body.len < @sizeOf(Description)) return null;
+    const description = std.mem.bytesToValue(Description, body[0..@sizeOf(Description)]);
+    const name = body[@sizeOf(Description)..];
+    if (name.len < description.name_len) return null;
+    return .{ .description = description, .name = name[0..description.name_len] };
+}
+
+/// The single framing point: prefix, then the fixed part, then the variable
+/// tail, contiguous in one buffer. Null when the packet would not fit — a
+/// packet is never split, so not fitting is a failure, not a continuation.
+fn frame(prefix: []const u8, fixed: []const u8, tail: []const u8, buffer: []u8) ?[]u8 {
+    const total = prefix.len + fixed.len + tail.len;
+    if (total > buffer.len) return null;
+    @memcpy(buffer[0..prefix.len], prefix);
+    @memcpy(buffer[prefix.len..][0..fixed.len], fixed);
+    @memcpy(buffer[prefix.len + fixed.len ..][0..tail.len], tail);
+    return buffer[0..total];
+}
+
+/// The bytes of a fixed part — empty for `void`, which is how an operation says
+/// "nothing but the verb".
+fn bytesOf(comptime T: type, value: *const T) []const u8 {
+    if (@sizeOf(T) == 0) return &.{};
+    return @as([*]const u8, @ptrCast(value))[0..@sizeOf(T)];
+}
+
+/// Read a fixed part out of a packet body. A zero-sized part always succeeds
+/// (there is nothing to be short of); anything else needs its full width.
+fn valueOf(comptime T: type, body: []const u8) ?T {
+    if (@sizeOf(T) == 0) return @as(T, undefined);
+    if (body.len < @sizeOf(T)) return null;
+    return std.mem.bytesToValue(T, body[0..@sizeOf(T)]);
+}
+
+// --- the specification ------------------------------------------------------
+
+/// One verb of a protocol. `request` and `reply` describe the bytes *after* the
+/// prefix; either may be `void`, meaning the verb (and its target) says it all.
+pub const OperationSpecification = struct {
+    name: []const u8,
+    request: type = void,
+    reply: type = void,
+};
+
+/// One event a provider pushes to its subscribers. `payload` is the bytes after
+/// the `Header`, and the whole packet must fit the push floor.
+pub const EventSpecification = struct {
+    name: []const u8,
+    payload: type = void,
+};
+
+/// What `Define` is given: the contract, whole.
+pub const Specification = struct {
+    /// The contract's name — the same word as its `/protocol/<name>` leaf and
+    /// its `library/protocol/` module.
+    name: []const u8,
+    version: u32,
+    operations: []const OperationSpecification = &.{},
+    events: []const EventSpecification = &.{},
+};
+
+const reserved_names = [_][]const u8{ "describe", "enumerate", "subscribe", "unsubscribe" };
+
+fn isReservedName(comptime name: []const u8) bool {
+    for (reserved_names) |reserved| {
+        if (std.mem.eql(u8, reserved, name)) return true;
+    }
+    return false;
+}
+
+/// Refuse a protocol type that carries the prefix inside itself. The header is
+/// folded into every packet, so a type that also holds one would send it twice
+/// and re-invent per-protocol addressing — the mistake the envelope exists to
+/// prevent.
+fn rejectStacking(comptime protocol: []const u8, comptime verb: []const u8, comptime T: type) void {
+    switch (@typeInfo(T)) {
+        .@"struct" => |info| for (info.fields) |field| {
+            if (field.type == Header or field.type == Status) @compileError(std.fmt.comptimePrint(
+                "protocol '{s}', verb '{s}': the envelope prefix is folded, not stacked — " ++
+                    "drop the {s} field '{s}' and use the packet's own Header.operation / Header.target",
+                .{ protocol, verb, @typeName(field.type), field.name },
+            ));
+        },
+        else => {},
+    }
+}
+
+fn nullDefault(comptime T: type) *const anyopaque {
+    const empty: ?T = null;
+    return @ptrCast(&empty);
+}
+
+// --- Define -----------------------------------------------------------------
+
+/// Build a protocol from its specification. Everything below happens at compile
+/// time; the generated type is what both sides of the conversation import.
+///
+/// ```zig
+/// pub const Protocol = envelope.Define(.{
+///     .name = "display",
+///     .version = 1,
+///     .operations = &.{
+///         .{ .name = "configure_layer", .request = ConfigureLayer, .reply = void },
+///         .{ .name = "blit", .request = Blit, .reply = void },
+///     },
+///     .events = &.{
+///         .{ .name = "layer_lost", .payload = LayerLost },
+///     },
+/// });
+/// ```
+///
+/// Refused at compile time, each with the protocol, the verb, and the numbers
+/// named in the message:
+///
+/// - a request or reply that does not fit `packet_maximum` once `prefix_size`
+///   is added (`.request = extern struct { bytes: [241]u8 }` — 241 + 16 = 257);
+/// - an event payload that does not fit `post_maximum` the same way
+///   (`.payload = extern struct { bytes: [49]u8 }` — 49 + 16 = 65);
+/// - a type that stacks the prefix instead of folding it (a `Header` field);
+/// - a verb named after a reserved one, or named twice.
+///
+/// A variable tail is bounded at *run* time instead, by `encodeRequest` and its
+/// siblings, because only the caller knows how long it is.
+pub fn Define(comptime specification: Specification) type {
+    comptime {
+        if (specification.name.len == 0) @compileError("a protocol needs a name");
+        if (specification.name.len > name_maximum) @compileError(std.fmt.comptimePrint(
+            "protocol '{s}': the name is {d} bytes, and a describe reply carries at most {d}",
+            .{ specification.name, specification.name.len, name_maximum },
+        ));
+
+        for (specification.operations, 0..) |operation, index| {
+            if (isReservedName(operation.name)) @compileError(std.fmt.comptimePrint(
+                "protocol '{s}': '{s}' is a reserved universal verb — the envelope already answers it",
+                .{ specification.name, operation.name },
+            ));
+            for (specification.operations[0..index]) |earlier| {
+                if (std.mem.eql(u8, earlier.name, operation.name)) @compileError(std.fmt.comptimePrint(
+                    "protocol '{s}': operation '{s}' is declared twice",
+                    .{ specification.name, operation.name },
+                ));
+            }
+            rejectStacking(specification.name, operation.name, operation.request);
+            rejectStacking(specification.name, operation.name, operation.reply);
+            if (!fitsPacket(operation.request)) @compileError(std.fmt.comptimePrint(
+                "protocol '{s}', operation '{s}': the request is {d} bytes and the header {d}, " ++
+                    "over the {d}-byte call floor — packets never fragment, so this has to shrink " ++
+                    "or move its bulk to shared memory",
+                .{ specification.name, operation.name, @sizeOf(operation.request), prefix_size, packet_maximum },
+            ));
+            if (!fitsPacket(operation.reply)) @compileError(std.fmt.comptimePrint(
+                "protocol '{s}', operation '{s}': the reply is {d} bytes and the status header {d}, " ++
+                    "over the {d}-byte call floor",
+                .{ specification.name, operation.name, @sizeOf(operation.reply), prefix_size, packet_maximum },
+            ));
+        }
+
+        for (specification.events, 0..) |event, index| {
+            for (specification.events[0..index]) |earlier| {
+                if (std.mem.eql(u8, earlier.name, event.name)) @compileError(std.fmt.comptimePrint(
+                    "protocol '{s}': event '{s}' is declared twice",
+                    .{ specification.name, event.name },
+                ));
+            }
+            rejectStacking(specification.name, event.name, event.payload);
+            if (!fitsPost(event.payload)) @compileError(std.fmt.comptimePrint(
+                "protocol '{s}', event '{s}': the payload is {d} bytes and the header {d}, " ++
+                    "over the {d}-byte push floor — an event carries the header too, so it is the " ++
+                    "payload that has to give",
+                .{ specification.name, event.name, @sizeOf(event.payload), prefix_size, post_maximum },
+            ));
+        }
+    }
+
+    return struct {
+        pub const protocol_name: []const u8 = specification.name;
+        pub const version: u32 = specification.version;
+
+        /// What a provider sizes its receive and reply buffers to. A packet's
+        /// fixed part may be far smaller, but any caller may send up to the
+        /// floor and a short buffer truncates rather than refuses.
+        pub const message_maximum: usize = packet_maximum;
+
+        /// The widest packet this protocol's fixed parts can actually produce,
+        /// prefix included — a diagnostic, and what a test pins.
+        pub const request_maximum: usize = widest(specification.operations, .request);
+        pub const reply_maximum: usize = widest(specification.operations, .reply);
+        pub const event_maximum: usize = blk: {
+            var widest_event: usize = prefix_size;
+            for (specification.events) |event| widest_event = @max(widest_event, prefix_size + @sizeOf(event.payload));
+            break :blk widest_event;
+        };
+
+        /// This protocol's verbs, numbered from `first_protocol_operation` in
+        /// declaration order.
+        pub const Operation = numbered(specification.operations, "name");
+
+        /// This protocol's events, numbered from `first_protocol_operation` in
+        /// their **own** space. Events travel only provider → subscriber over
+        /// `ipc_send` and operations only client → provider over `ipc_call`, so
+        /// the direction already tells the two apart; separate spaces mean
+        /// appending an operation can never renumber a shipped event.
+        pub const Event = numbered(specification.events, "name");
+
+        /// The bytes after the `Header` on a request for `operation`.
+        pub fn RequestOf(comptime operation: Operation) type {
+            return specification.operations[indexOf(@intFromEnum(operation))].request;
+        }
+
+        /// The bytes after the `Status` on the reply to `operation`.
+        pub fn ReplyOf(comptime operation: Operation) type {
+            return specification.operations[indexOf(@intFromEnum(operation))].reply;
+        }
+
+        /// The bytes after the `Header` on an `event` packet.
+        pub fn PayloadOf(comptime event: Event) type {
+            return specification.events[indexOf(@intFromEnum(event))].payload;
+        }
+
+        // --- client side ----------------------------------------------------
+
+        /// Frame `[Header][request][tail]`. `tail` is the variable part (a path,
+        /// write bytes); pass `&.{}` when the verb has none. Null if the packet
+        /// would exceed the buffer or the call floor.
+        pub fn encodeRequest(
+            comptime operation: Operation,
+            target: u64,
+            request: RequestOf(operation),
+            tail: []const u8,
+            buffer: []u8,
+        ) ?[]u8 {
+            const header = Header{ .operation = @intFromEnum(operation), .target = target };
+            const packet = frame(std.mem.asBytes(&header), bytesOf(RequestOf(operation), &request), tail, buffer) orelse return null;
+            return if (packet.len > packet_maximum) null else packet;
+        }
+
+        /// Frame `[Status][reply][tail]` — the provider's answer, for a provider
+        /// that composes its own reply rather than using `Provider.dispatch`.
+        pub fn encodeReply(
+            comptime operation: Operation,
+            status: i32,
+            reply: ReplyOf(operation),
+            tail: []const u8,
+            buffer: []u8,
+        ) ?[]u8 {
+            const fixed = bytesOf(ReplyOf(operation), &reply);
+            const head = Status{ .status = status, .len = @intCast(fixed.len + tail.len) };
+            const packet = frame(std.mem.asBytes(&head), fixed, tail, buffer) orelse return null;
+            return if (packet.len > packet_maximum) null else packet;
+        }
+
+        /// Frame `[Header][payload]` for an asynchronous push. Null if it would
+        /// exceed the buffer or the push floor — an event that does not fit is
+        /// dropped at the source, never split.
+        pub fn encodeEvent(
+            comptime event: Event,
+            target: u64,
+            payload: PayloadOf(event),
+            buffer: []u8,
+        ) ?[]u8 {
+            const header = Header{ .operation = @intFromEnum(event), .target = target };
+            const packet = frame(std.mem.asBytes(&header), bytesOf(PayloadOf(event), &payload), &.{}, buffer) orelse return null;
+            return if (packet.len > post_maximum) null else packet;
+        }
+
+        /// Which of this protocol's verbs a packet names — null for a reserved
+        /// verb, or for a number this protocol does not define.
+        pub fn operationOf(packet: []const u8) ?Operation {
+            const header = headerOf(packet) orelse return null;
+            const index = header.operation -% first_protocol_operation;
+            if (header.operation < first_protocol_operation or index >= specification.operations.len) return null;
+            return @enumFromInt(header.operation);
+        }
+
+        /// Which of this protocol's events a pushed packet carries.
+        pub fn eventOf(packet: []const u8) ?Event {
+            const header = headerOf(packet) orelse return null;
+            const index = header.operation -% first_protocol_operation;
+            if (header.operation < first_protocol_operation or index >= specification.events.len) return null;
+            return @enumFromInt(header.operation);
+        }
+
+        /// The fixed request part of a packet already known to name `operation`.
+        pub fn decodeRequest(comptime operation: Operation, packet: []const u8) ?RequestOf(operation) {
+            if (packet.len < prefix_size) return null;
+            return valueOf(RequestOf(operation), packet[prefix_size..]);
+        }
+
+        /// The bytes after the fixed request part — empty when there are none.
+        pub fn requestTail(comptime operation: Operation, packet: []const u8) []const u8 {
+            const start = prefix_size + @sizeOf(RequestOf(operation));
+            return if (packet.len <= start) &.{} else packet[start..];
+        }
+
+        /// The fixed reply part of a reply packet. Null on a short packet; the
+        /// caller checks `statusOf(packet).status` for the provider's verdict.
+        pub fn decodeReply(comptime operation: Operation, packet: []const u8) ?ReplyOf(operation) {
+            if (packet.len < prefix_size) return null;
+            return valueOf(ReplyOf(operation), packet[prefix_size..]);
+        }
+
+        /// The bytes after the fixed reply part, clipped to what `Status.len`
+        /// says actually arrived.
+        pub fn replyTail(comptime operation: Operation, packet: []const u8) []const u8 {
+            const status = statusOf(packet) orelse return &.{};
+            const start = prefix_size + @sizeOf(ReplyOf(operation));
+            const end = @min(packet.len, prefix_size + @as(usize, status.len));
+            return if (end <= start) &.{} else packet[start..end];
+        }
+
+        /// The payload of a pushed packet already known to carry `event`.
+        pub fn decodeEvent(comptime event: Event, packet: []const u8) ?PayloadOf(event) {
+            if (packet.len < prefix_size) return null;
+            return valueOf(PayloadOf(event), packet[prefix_size..]);
+        }
+
+        // --- provider side --------------------------------------------------
+
+        /// This protocol's dispatch table, bound to the provider's own state
+        /// type. `describe` is answered here, from the specification; every verb
+        /// this provider left null answers `-ENOSYS`, which is what makes the
+        /// reserved verbs mean the same thing at every provider in the system.
+        ///
+        /// ```zig
+        /// const Serve = Protocol.Provider(*Server);
+        /// const handlers = Serve.Handlers{ .blit = onBlit, .configure_layer = onConfigureLayer };
+        /// const reply_len = Serve.dispatch(server, handlers, message, sender, capability, reply);
+        /// ```
+        ///
+        /// A handler returns the number of `answer.tail()` bytes it wrote, or a
+        /// negative errno.
+        pub fn Provider(comptime Context: type) type {
+            return struct {
+                /// A reserved verb a provider chooses to implement itself.
+                /// `enumerate` writes its targets into the tail; `subscribe`
+                /// takes the subscriber's endpoint from `invocation.capability`.
+                pub const ReservedHandler = *const fn (Context, Invocation(void), Answer(void)) isize;
+
+                /// One optional handler per verb, named exactly as the verb,
+                /// plus the reserved verbs the envelope cannot answer alone.
+                pub const Handlers = handlerTable(Context);
+
+                /// Answer one received packet: writes `[Status][reply][tail]`
+                /// into `reply` and returns its length. Zero means the reply
+                /// buffer could not even hold a status, so nothing was written.
+                pub fn dispatch(
+                    context: Context,
+                    handlers: Handlers,
+                    packet: []const u8,
+                    sender: u32,
+                    capability: ?usize,
+                    reply: []u8,
+                ) usize {
+                    if (reply.len < prefix_size) return 0;
+                    const header = headerOf(packet) orelse return refuse(reply, -EPROTO);
+                    const body = packet[prefix_size..];
+
+                    if (header.operation == operation_describe) return describeInto(reply);
+
+                    inline for (specification.operations, 0..) |operation, index| {
+                        if (header.operation == first_protocol_operation + index) {
+                            return invoke(
+                                Context,
+                                operation.request,
+                                operation.reply,
+                                @field(handlers, operation.name),
+                                context,
+                                header.target,
+                                body,
+                                sender,
+                                capability,
+                                reply,
+                            );
+                        }
+                    }
+
+                    const reserved: ?ReservedHandler = switch (header.operation) {
+                        operation_enumerate => handlers.enumerate,
+                        operation_subscribe => handlers.subscribe,
+                        operation_unsubscribe => handlers.unsubscribe,
+                        else => null,
+                    };
+                    return invoke(Context, void, void, reserved, context, header.target, body, sender, capability, reply);
+                }
+            };
+        }
+
+        // Shared by the protocol verbs and the reserved ones: decode, hand the
+        // handler a typed invocation, stamp the status. One place, so a reserved
+        // verb and a protocol verb behave identically.
+        fn invoke(
+            comptime Context: type,
+            comptime RequestType: type,
+            comptime ReplyType: type,
+            handler: ?*const fn (Context, Invocation(RequestType), Answer(ReplyType)) isize,
+            context: Context,
+            target: u64,
+            body: []const u8,
+            sender: u32,
+            capability: ?usize,
+            reply: []u8,
+        ) usize {
+            const call = handler orelse return refuse(reply, -ENOSYS);
+            const request = valueOf(RequestType, body) orelse return refuse(reply, -EPROTO);
+            if (reply.len < prefix_size + @sizeOf(ReplyType)) return refuse(reply, -EPROTO);
+            const produced = call(context, .{
+                .target = target,
+                .request = request,
+                .tail = body[@min(@sizeOf(RequestType), body.len)..],
+                .sender = sender,
+                .capability = capability,
+            }, .{ .buffer = reply[prefix_size..] });
+            if (produced < 0) return refuse(reply, @intCast(produced));
+            return succeed(reply, @sizeOf(ReplyType) + @as(usize, @intCast(produced)));
+        }
+
+        fn describeInto(reply: []u8) usize {
+            const description = Description{
+                .version = specification.version,
+                .operation_count = specification.operations.len,
+                .event_count = specification.events.len,
+                .name_len = specification.name.len,
+            };
+            const total = @sizeOf(Description) + specification.name.len;
+            if (reply.len < prefix_size + total) return refuse(reply, -EPROTO);
+            @memcpy(reply[prefix_size..][0..@sizeOf(Description)], std.mem.asBytes(&description));
+            @memcpy(reply[prefix_size + @sizeOf(Description) ..][0..specification.name.len], specification.name);
+            return succeed(reply, total);
+        }
+
+        // "describe" is answered by the envelope, so it is the one reserved verb
+        // with no slot in the table.
+        const implementable_reserved = [_][]const u8{ "enumerate", "subscribe", "unsubscribe" };
+
+        fn handlerTable(comptime Context: type) type {
+            const count = specification.operations.len + implementable_reserved.len;
+            var names: [count][]const u8 = undefined;
+            var types: [count]type = undefined;
+            var attributes: [count]std.builtin.Type.StructField.Attributes = undefined;
+            for (specification.operations, 0..) |operation, index| {
+                const Handler = *const fn (Context, Invocation(operation.request), Answer(operation.reply)) isize;
+                names[index] = operation.name;
+                types[index] = ?Handler;
+                attributes[index] = .{ .default_value_ptr = nullDefault(Handler) };
+            }
+            const Reserved = *const fn (Context, Invocation(void), Answer(void)) isize;
+            for (implementable_reserved, 0..) |name, offset| {
+                const slot = specification.operations.len + offset;
+                names[slot] = name;
+                types[slot] = ?Reserved;
+                attributes[slot] = .{ .default_value_ptr = nullDefault(Reserved) };
+            }
+            const frozen_names = names;
+            const frozen_types = types;
+            const frozen_attributes = attributes;
+            return @Struct(.auto, null, &frozen_names, &frozen_types, &frozen_attributes);
+        }
+    };
+}
+
+// --- the provider's view of one packet --------------------------------------
+
+/// What a provider's handler is given.
+pub fn Invocation(comptime RequestType: type) type {
+    return struct {
+        /// Object addressing within this provider — the packet's `Header.target`.
+        target: u64,
+        /// The fixed request part, already decoded.
+        request: RequestType,
+        /// The bytes after it: a path, write data, a name.
+        tail: []const u8,
+        /// The kernel-stamped badge of the caller. The only source identity
+        /// there is — no protocol defines a sender field — so per-client state
+        /// is keyed on this.
+        sender: u32,
+        /// A capability the call carried: a subscriber's endpoint, a DMA
+        /// region. Only the synchronous call path can move one.
+        capability: ?usize,
+    };
+}
+
+/// Where a provider's handler writes its answer. The `Status` in front of it is
+/// the dispatcher's to stamp — a handler never writes its own.
+pub fn Answer(comptime ReplyType: type) type {
+    return struct {
+        buffer: []u8,
+
+        const fixed_size = @sizeOf(ReplyType);
+
+        /// Write the fixed reply part. A `void` reply writes nothing.
+        pub fn set(self: @This(), reply: ReplyType) void {
+            if (fixed_size == 0) return;
+            @memcpy(self.buffer[0..fixed_size], bytesOf(ReplyType, &reply));
+        }
+
+        /// Room for the variable tail; the handler returns how much of it it used.
+        pub fn tail(self: @This()) []u8 {
+            return self.buffer[fixed_size..];
+        }
+    };
+}
+
+fn refuse(reply: []u8, status: i32) usize {
+    const head = Status{ .status = status, .len = 0 };
+    @memcpy(reply[0..prefix_size], std.mem.asBytes(&head));
+    return prefix_size;
+}
+
+fn succeed(reply: []u8, len: usize) usize {
+    const head = Status{ .status = 0, .len = @intCast(len) };
+    @memcpy(reply[0..prefix_size], std.mem.asBytes(&head));
+    return prefix_size + len;
+}
+
+/// The widest `[prefix][fixed]` over a set of operations, on one side.
+fn widest(comptime operations: []const OperationSpecification, comptime side: enum { request, reply }) usize {
+    var found: usize = prefix_size;
+    for (operations) |operation| {
+        const size = switch (side) {
+            .request => @sizeOf(operation.request),
+            .reply => @sizeOf(operation.reply),
+        };
+        found = @max(found, prefix_size + size);
+    }
+    return found;
+}
+
+/// An enum over `specifications`, tagged by their `name` field, numbered from
+/// `first_protocol_operation` in declaration order.
+fn numbered(comptime specifications: anytype, comptime field: []const u8) type {
+    var names: [specifications.len][]const u8 = undefined;
+    var values: [specifications.len]u32 = undefined;
+    for (specifications, 0..) |specification, index| {
+        names[index] = @field(specification, field);
+        values[index] = first_protocol_operation + index;
+    }
+    const frozen_names = names;
+    const frozen_values = values;
+    return @Enum(u32, .exhaustive, &frozen_names, &frozen_values);
+}
+
+/// A verb's position in its declaration list, from its wire number.
+fn indexOf(comptime operation: u32) usize {
+    return operation - first_protocol_operation;
+}
+
+// --- tests ------------------------------------------------------------------
+
+const testing = std.testing;
+
+const Produce = extern struct { count: u32, flags: u32 = 0 };
+const Produced = extern struct { total: u64 };
+const Changed = extern struct { kind: u32, value: u32 };
+
+const Sample = Define(.{
+    .name = "sample",
+    .version = 3,
+    .operations = &.{
+        .{ .name = "produce", .request = Produce, .reply = Produced },
+        .{ .name = "reset" },
+    },
+    .events = &.{
+        .{ .name = "changed", .payload = Changed },
+    },
+});
+
+test "the prefix is 16 bytes in both directions" {
+    try testing.expectEqual(@as(usize, 16), @sizeOf(Header));
+    try testing.expectEqual(@as(usize, 16), @sizeOf(Status));
+    try testing.expectEqual(@as(usize, 16), prefix_size);
+    try testing.expectEqual(@as(usize, 256), packet_maximum);
+    try testing.expectEqual(@as(usize, 64), post_maximum);
+}
+
+test "verb numbering skips the reserved range" {
+    try testing.expectEqual(@as(u32, 16), first_protocol_operation);
+    try testing.expectEqual(@as(u32, 16), @intFromEnum(Sample.Operation.produce));
+    try testing.expectEqual(@as(u32, 17), @intFromEnum(Sample.Operation.reset));
+    // Events are numbered in their own space, so appending an operation can
+    // never renumber a shipped event.
+    try testing.expectEqual(@as(u32, 16), @intFromEnum(Sample.Event.changed));
+    for ([_]u32{ operation_describe, operation_enumerate, operation_subscribe, operation_unsubscribe }) |reserved| {
+        try testing.expect(reserved < first_protocol_operation);
+    }
+}
+
+test "request round trip, header folded and tail carried" {
+    var buffer: [packet_maximum]u8 = undefined;
+    const packet = Sample.encodeRequest(.produce, 42, .{ .count = 7 }, "tail bytes", &buffer).?;
+    try testing.expectEqual(prefix_size + @sizeOf(Produce) + "tail bytes".len, packet.len);
+
+    const header = headerOf(packet).?;
+    try testing.expectEqual(@as(u32, 16), header.operation);
+    try testing.expectEqual(@as(u64, 42), header.target);
+    try testing.expectEqual(Sample.Operation.produce, Sample.operationOf(packet).?);
+
+    const request = Sample.decodeRequest(.produce, packet).?;
+    try testing.expectEqual(@as(u32, 7), request.count);
+    try testing.expectEqualStrings("tail bytes", Sample.requestTail(.produce, packet));
+}
+
+test "reply round trip" {
+    var buffer: [packet_maximum]u8 = undefined;
+    const packet = Sample.encodeReply(.produce, 0, .{ .total = 99 }, "more", &buffer).?;
+    const status = statusOf(packet).?;
+    try testing.expectEqual(@as(i32, 0), status.status);
+    try testing.expectEqual(@as(u32, @sizeOf(Produced) + "more".len), status.len);
+    try testing.expectEqual(@as(u64, 99), Sample.decodeReply(.produce, packet).?.total);
+    try testing.expectEqualStrings("more", Sample.replyTail(.produce, packet));
+}
+
+test "a void request and reply carry nothing but the verb" {
+    var buffer: [packet_maximum]u8 = undefined;
+    const packet = Sample.encodeRequest(.reset, 0, {}, &.{}, &buffer).?;
+    try testing.expectEqual(prefix_size, packet.len);
+    try testing.expectEqual(Sample.Operation.reset, Sample.operationOf(packet).?);
+    try testing.expectEqual(@as(usize, 0), Sample.requestTail(.reset, packet).len);
+}
+
+test "event round trip within the push floor" {
+    var buffer: [post_maximum]u8 = undefined;
+    const packet = Sample.encodeEvent(.changed, 0, .{ .kind = 1, .value = 2 }, &buffer).?;
+    try testing.expectEqual(prefix_size + @sizeOf(Changed), packet.len);
+    try testing.expect(packet.len <= post_maximum);
+    try testing.expectEqual(Sample.Event.changed, Sample.eventOf(packet).?);
+    try testing.expectEqual(@as(u32, 2), Sample.decodeEvent(.changed, packet).?.value);
+}
+
+// A provider over a trivial context, to drive the generated dispatch table.
+const Counter = struct {
+    total: u64 = 0,
+
+    fn onProduce(self: *Counter, invocation: Invocation(Produce), answer: Answer(Produced)) isize {
+        self.total += invocation.request.count;
+        answer.set(.{ .total = self.total });
+        const note = "counted";
+        @memcpy(answer.tail()[0..note.len], note);
+        return note.len;
+    }
+};
+
+const CounterProvider = Sample.Provider(*Counter);
+
+test "dispatch reaches a handler and stamps the status" {
+    var counter = Counter{};
+    const handlers = CounterProvider.Handlers{ .produce = Counter.onProduce };
+
+    var request: [packet_maximum]u8 = undefined;
+    const packet = Sample.encodeRequest(.produce, 0, .{ .count = 5 }, &.{}, &request).?;
+    var reply: [packet_maximum]u8 = undefined;
+    const len = CounterProvider.dispatch(&counter, handlers, packet, 3, null, &reply);
+
+    const answered = reply[0..len];
+    try testing.expectEqual(@as(i32, 0), statusOf(answered).?.status);
+    try testing.expectEqual(@as(u64, 5), Sample.decodeReply(.produce, answered).?.total);
+    try testing.expectEqualStrings("counted", Sample.replyTail(.produce, answered));
+}
+
+test "describe is answered by the envelope, not the provider" {
+    var counter = Counter{};
+    const handlers = CounterProvider.Handlers{ .produce = Counter.onProduce };
+
+    var request: [packet_maximum]u8 = undefined;
+    const packet = encodeDescribe(&request).?;
+    var reply: [packet_maximum]u8 = undefined;
+    const len = CounterProvider.dispatch(&counter, handlers, packet, 3, null, &reply);
+
+    const described = decodeDescribe(reply[0..len]).?;
+    try testing.expectEqualStrings("sample", described.name);
+    try testing.expectEqual(@as(u32, 3), described.description.version);
+    try testing.expectEqual(@as(u32, 2), described.description.operation_count);
+    try testing.expectEqual(@as(u32, 1), described.description.event_count);
+}
+
+test "an unimplemented or unknown verb answers -ENOSYS" {
+    var counter = Counter{};
+    const handlers = CounterProvider.Handlers{ .produce = Counter.onProduce };
+    var reply: [packet_maximum]u8 = undefined;
+
+    // A verb this protocol declares but this provider left null.
+    var request: [packet_maximum]u8 = undefined;
+    const declared = Sample.encodeRequest(.reset, 0, {}, &.{}, &request).?;
+    var len = CounterProvider.dispatch(&counter, handlers, declared, 3, null, &reply);
+    try testing.expectEqual(@as(i32, -ENOSYS), statusOf(reply[0..len]).?.status);
+
+    // A number no verb of this protocol wears.
+    const stranger = Header{ .operation = first_protocol_operation + 900 };
+    len = CounterProvider.dispatch(&counter, handlers, std.mem.asBytes(&stranger), 3, null, &reply);
+    try testing.expectEqual(@as(i32, -ENOSYS), statusOf(reply[0..len]).?.status);
+
+    // A reserved verb the provider does not implement answers the same way.
+    const enumerate = Header{ .operation = operation_enumerate };
+    len = CounterProvider.dispatch(&counter, handlers, std.mem.asBytes(&enumerate), 3, null, &reply);
+    try testing.expectEqual(@as(i32, -ENOSYS), statusOf(reply[0..len]).?.status);
+}
+
+test "a truncated packet answers -EPROTO" {
+    var counter = Counter{};
+    const handlers = CounterProvider.Handlers{ .produce = Counter.onProduce };
+    var reply: [packet_maximum]u8 = undefined;
+
+    // Names `produce`, but stops before the request it promises.
+    const header = Header{ .operation = @intFromEnum(Sample.Operation.produce) };
+    const len = CounterProvider.dispatch(&counter, handlers, std.mem.asBytes(&header), 3, null, &reply);
+    try testing.expectEqual(@as(i32, -EPROTO), statusOf(reply[0..len]).?.status);
+}
+
+// The size rule, exercised directly. `Define` turns exactly these predicates
+// into compile errors, which a test cannot catch — so the predicate is what the
+// test pins, and the boundary protocol below proves the compile-time half from
+// the other side. The negative example, spelled out: giving `Define` an
+// operation with `.request = extern struct { bytes: [241]u8 }`, or an event with
+// `.payload = extern struct { bytes: [49]u8 }`, fails to compile with the
+// protocol, the verb, and the two numbers named in the message.
+test "a subscribe carries its interest mask in the reserved verb's tail" {
+    var buffer: [packet_maximum]u8 = undefined;
+    const packet = encodeSubscribe(0b101, &buffer).?;
+    try testing.expectEqual(operation_subscribe, headerOf(packet).?.operation);
+    try testing.expectEqual(@as(u32, 0b101), decodeSubscribe(packet[prefix_size..]).interest);
+    // No body at all — and a body too short to be one — read as "every event",
+    // which is what a subscriber that named nothing wants.
+    try testing.expectEqual(@as(u32, 0), decodeSubscribe(&.{}).interest);
+    try testing.expectEqual(@as(u32, 0), decodeSubscribe(&.{ 1, 2 }).interest);
+
+    const bare = encodeUnsubscribe(&buffer).?;
+    try testing.expectEqual(operation_unsubscribe, headerOf(bare).?.operation);
+    try testing.expectEqual(prefix_size, bare.len);
+}
+
+test "the floor counts the header once, and the boundary is exact" {
+    try testing.expect(fitsPacket(extern struct { bytes: [240]u8 }));
+    try testing.expect(!fitsPacket(extern struct { bytes: [241]u8 }));
+    try testing.expect(fitsPost(extern struct { bytes: [48]u8 }));
+    try testing.expect(!fitsPost(extern struct { bytes: [49]u8 }));
+    try testing.expect(fitsPacket(void));
+    try testing.expect(fitsPost(void));
+}
+
+const WidestRequest = extern struct { bytes: [packet_maximum - prefix_size]u8 };
+const WidestEvent = extern struct { bytes: [post_maximum - prefix_size]u8 };
+
+// A protocol sitting exactly on both floors. That this compiles at all is the
+// positive half of the compile-time check.
+const Boundary = Define(.{
+    .name = "boundary",
+    .version = 1,
+    .operations = &.{.{ .name = "fill", .request = WidestRequest, .reply = WidestRequest }},
+    .events = &.{.{ .name = "filled", .payload = WidestEvent }},
+});
+
+test "a protocol may sit exactly on the floor" {
+    try testing.expectEqual(packet_maximum, Boundary.request_maximum);
+    try testing.expectEqual(packet_maximum, Boundary.reply_maximum);
+    try testing.expectEqual(post_maximum, Boundary.event_maximum);
+
+    var buffer: [packet_maximum]u8 = undefined;
+    const packet = Boundary.encodeRequest(.fill, 0, .{ .bytes = @splat(0xAB) }, &.{}, &buffer).?;
+    try testing.expectEqual(packet_maximum, packet.len);
+    try testing.expectEqual(@as(u8, 0xAB), Boundary.decodeRequest(.fill, packet).?.bytes[239]);
+
+    // One byte of tail past the floor is refused at run time, not truncated.
+    try testing.expect(Boundary.encodeRequest(.fill, 0, .{ .bytes = @splat(0) }, "x", &buffer) == null);
+
+    var post: [post_maximum]u8 = undefined;
+    const event = Boundary.encodeEvent(.filled, 0, .{ .bytes = @splat(1) }, &post).?;
+    try testing.expectEqual(post_maximum, event.len);
+}
+
+test "a protocol's own sizes are reported prefix-included" {
+    try testing.expectEqual(prefix_size + @sizeOf(Produce), Sample.request_maximum);
+    try testing.expectEqual(prefix_size + @sizeOf(Produced), Sample.reply_maximum);
+    try testing.expectEqual(prefix_size + @sizeOf(Changed), Sample.event_maximum);
+    try testing.expectEqual(packet_maximum, Sample.message_maximum);
+    try testing.expectEqualStrings("sample", Sample.protocol_name);
+}

library/protocol/input/input-protocol.zig

@@ -4,25 +4,30 @@
 //! **subscriber** (any program) that subscribes and is then pushed each event.
 //!
 //! The service handles several device classes over one endpoint. Each class has its own
-//! typed event (`KeyEvent`, `MouseEvent`, `JoystickEvent`); they all travel in a common
+//! typed event (`KeyEvent`, `MouseEvent`, `JoystickEvent`); a subscriber declares which
-//! `InputEvent` envelope tagged with a `DeviceKind`, so the fan-out path is one code path
+//! classes it wants with a `device_mask`, and the service routes accordingly.
-//! and a subscriber can take a mix of devices on a single stream. A subscriber declares
-//! which classes it wants with a `device_mask`, and the service routes accordingly.
 //!
-//! Two message shapes ride over the endpoint, tagged by `Operation`, like the
+//! Three shapes ride over the channel, and the envelope names all three
-//! [VFS protocol](../vfs/protocol.zig):
+//! (docs/os-development/protocol-namespace.md):
 //!
-//! - **subscribe / publish**: a synchronous `ipc_call` carrying a `Request`. `subscribe`
+//! - **subscribe** is the *reserved* verb, not one of this protocol's own: its shape — a
-//!   hands the service the subscriber's own endpoint as a capability (`send_cap`) and a
+//!   synchronous call whose attached capability is the subscriber's endpoint — is exactly
-//!   `device_mask`; `publish` carries an `InputEvent`. The reply is a `Reply`.
+//!   what `envelope.operation_subscribe` means everywhere. The interest mask travels as the
-//! - **delivery**: the service pushes each `InputEvent` to every interested subscriber with
+//!   packet's tail (`envelope.Subscription`), because a reserved verb carries no typed
-//!   the asynchronous `ipc_send` — no reply owed, and a dead subscriber can never stall the
+//!   request; what this protocol supplies is the *meaning* of its bits — the device classes.
-//!   broadcast. Received in the subscriber's buffer with `Received.isMessage()` set.
+//! - **publish** is this protocol's one verb: a source sends one `InputEvent` and the
+//!   service answers at once, so publishing never blocks on a slow subscriber.
+//! - **delivery** is an event push: the service `ipc_send`s each event to every interested
+//!   subscriber — no reply owed, so a dead subscriber can never stall the broadcast. The
+//!   packet is the folded header plus the typed event, and **the device class is the
+//!   header's operation**: one event per class, so a subscriber reads the kind from the
+//!   packet rather than from a tag inside the payload.
 //!
-//! This is a danos-native contract, shared by the input service, the `runtime.input`
+//! `Header.target` is unused (0) in both directions: the service is the only object either
-//! client helpers, and every source/subscriber. Everything fits one IPC message.
+//! side addresses.
 
 const std = @import("std");
+const envelope = @import("envelope");
 
 /// The classes of input device the service fans out. Each names a typed event and a bit in
 /// the subscription mask.
@@ -242,14 +247,17 @@ pub const JoystickEvent = extern struct {
     buttons: u32, // current pressed-button bitmask
 };
 
-// --- the common envelope ----------------------------------------------------
+// --- the tagged union of the three ------------------------------------------
 
 /// The largest per-device event, so `InputEvent` can hold any of them inline.
 pub const max_event_size: usize = @max(@sizeOf(KeyEvent), @max(@sizeOf(MouseEvent), @sizeOf(JoystickEvent)));
 
-/// The tagged envelope broadcast to subscribers: a `DeviceKind` plus the raw bytes of the
+/// One event of any class: a `DeviceKind` plus the raw bytes of the matching per-device
-/// matching per-device event. Decode it with `asKeyboard`/`asMouse`/`asJoystick` (each
+/// event. This is what a source `publish`es (one verb for all three classes) and what a
-/// returns null unless `device` matches), or build one with the `from*` constructors.
+/// subscriber's helper hands back after decoding a delivery — on the *delivery* wire the
+/// class is the packet header's operation instead, so this tag never travels there. Decode
+/// it with `asKeyboard`/`asMouse`/`asJoystick` (each returns null unless `device` matches),
+/// or build one with the `from*` constructors.
 pub const InputEvent = extern struct {
     device: u32, // a DeviceKind
     _padding: u32 = 0,
@@ -285,35 +293,88 @@ pub const InputEvent = extern struct {
     }
 };
 
-// --- request / reply --------------------------------------------------------
+// --- the contract -----------------------------------------------------------
 
-/// Which side of a request this is.
+pub const Protocol = envelope.Define(.{
-pub const Operation = enum(u32) {
+    .name = "input",
-    subscribe = 0, // register the caller's endpoint (send_cap) for the classes in device_mask
+    .version = 1,
-    publish = 1, // a source submits `event` to broadcast to interested subscribers
+    .operations = &.{
-};
+        // A source submits one event; the service broadcasts it to whoever wants that class.
+        .{ .name = "publish", .request = InputEvent },
+    },
+    .events = &.{
+        // One per device class: the class is the packet's operation, the typed event its
+        // payload. The push floor is 64 bytes and the header spends 16 of them, so the
+        // widest of these — the 28-byte mouse event — leaves the budget with room to spare.
+        .{ .name = "keyboard", .payload = KeyEvent },
+        .{ .name = "mouse", .payload = MouseEvent },
+        .{ .name = "joystick", .payload = JoystickEvent },
+    },
+});
 
-/// Request header. For `subscribe`, `device_mask` is the OR of `device_*` bits the caller
+pub const Operation = Protocol.Operation;
-/// wants (0 means all) and the caller's receive endpoint travels as the call's capability;
+pub const Event = Protocol.Event;
-/// `event` is ignored. For `publish`, `event` is the event to broadcast.
+pub const message_maximum: usize = Protocol.message_maximum;
-pub const Request = extern struct {
-    operation: u32, // an Operation
-    device_mask: u32 = 0, // subscribe: interested device classes (0 => all)
-    event: InputEvent = .{ .device = 0 },
-};
-
-/// Reply header. `status` is 0 on success or a negative errno.
-pub const Reply = extern struct {
-    status: i32,
-    _padding: u32 = 0,
-};
-
-pub const request_size: usize = @sizeOf(Request);
-pub const reply_size: usize = @sizeOf(Reply);
 pub const event_size: usize = @sizeOf(InputEvent);
 
-comptime {
+/// The event class a `DeviceKind` value (as it appears in `InputEvent.device`) is delivered
-    // The delivery path posts a bare InputEvent through ipc_send, so it must fit an
+/// as. Null for a value no class claims, which is delivered to nobody.
-    // endpoint's async payload slot (POST_MAXIMUM is 64).
+pub fn eventOfDevice(device: u32) ?Event {
-    if (event_size > 64) @compileError("InputEvent must fit the ipc_send payload (POST_MAXIMUM)");
+    return switch (device) {
+        @intFromEnum(DeviceKind.keyboard) => .keyboard,
+        @intFromEnum(DeviceKind.mouse) => .mouse,
+        @intFromEnum(DeviceKind.joystick) => .joystick,
+        else => null,
+    };
+}
+
+/// Frame a `subscribe` request: the reserved verb's header, then the interest mask. Null if
+/// the buffer is too small. The mask itself is the envelope's `Subscription` — the interest
+/// a reserved subscribe carries is universal, and the *meaning* of its bits (here: the
+/// device classes above) is what each protocol supplies. Kept as a named helper because
+/// `device_mask` is what an input caller calls it.
+pub fn encodeSubscribe(device_mask: u32, buffer: []u8) ?[]u8 {
+    return envelope.encodeSubscribe(device_mask, buffer);
+}
+
+test "an event of every class fits the push floor, header included" {
+    // What the hand-rolled comptime assert used to say about `InputEvent`, now
+    // said by `Define` about each typed event — and counting the header, which
+    // the old check did not.
+    try std.testing.expectEqual(envelope.prefix_size + @sizeOf(MouseEvent), Protocol.event_maximum);
+    try std.testing.expect(Protocol.event_maximum <= envelope.post_maximum);
+}
+
+test "the verb numbering, and the class an event carries" {
+    try std.testing.expectEqual(@as(u32, 16), @intFromEnum(Operation.publish));
+    // Events number in their own space, so the three classes start at 16 too.
+    try std.testing.expectEqual(@as(u32, 16), @intFromEnum(Event.keyboard));
+    try std.testing.expectEqual(@as(u32, 17), @intFromEnum(Event.mouse));
+    try std.testing.expectEqual(@as(u32, 18), @intFromEnum(Event.joystick));
+    // subscribe is the RESERVED verb, below the protocol range entirely.
+    try std.testing.expectEqual(@as(u32, 2), envelope.operation_subscribe);
+
+    var buffer: [envelope.post_maximum]u8 = undefined;
+    const packet = Protocol.encodeEvent(.mouse, 0, .{
+        .kind = @intFromEnum(MouseEventKind.motion),
+        .button = 0,
+        .dx = 3,
+        .dy = -4,
+        .scroll_x = 0,
+        .scroll_y = 0,
+        .buttons = 0,
+    }, &buffer).?;
+    try std.testing.expectEqual(Event.mouse, Protocol.eventOf(packet).?);
+    try std.testing.expectEqual(@as(i32, -4), Protocol.decodeEvent(.mouse, packet).?.dy);
+}
+
+test "a subscribe carries its mask in the tail of the reserved verb" {
+    var buffer: [envelope.packet_maximum]u8 = undefined;
+    const packet = encodeSubscribe(device_mouse, &buffer).?;
+    try std.testing.expectEqual(envelope.operation_subscribe, envelope.headerOf(packet).?.operation);
+    // The provider side of this is the service harness's, which reads the same
+    // interest mask out of the tail for every protocol.
+    try std.testing.expectEqual(device_mouse, envelope.decodeSubscribe(packet[envelope.prefix_size..]).interest);
+    // A caller that sent nothing at all reads as the every-class mask.
+    try std.testing.expectEqual(@as(u32, 0), envelope.decodeSubscribe(&.{}).interest);
 }

library/protocol/power/power-protocol.zig

@@ -1,68 +1,104 @@
-//! The power protocol (docs/power.md): system power's domain-named surface,
+//! The power protocol (docs/os-development/power.md): system power's
-//! registered under `ServiceId.power`. On x86 the acpi service serves it; on
+//! domain-named surface, bound at `/protocol/power`. On x86 the acpi service
-//! ARM a PSCI/mailbox service will register the same id — subscribers never
+//! provides it; on ARM a PSCI/mailbox service will bind the same name —
-//! learn which firmware they are on (docs/discovery.md — firmware neutrality).
+//! subscribers never learn which firmware they are on (docs/discovery.md —
-//! The vfs-protocol pattern: extern-struct messages, a version, reserved fields.
+//! firmware neutrality), which is the whole point of naming the contract rather
+//! than the provider (docs/os-development/protocol-namespace.md).
+//!
+//! Defined through the envelope, so every packet begins with the folded
+//! `Header`. Three shapes ride the channel, and the envelope names all three:
+//!
+//! - **subscribe** is the *reserved* verb, not one of this protocol's own: a
+//!   synchronous call whose attached capability is the subscriber's endpoint is
+//!   exactly what `envelope.operation_subscribe` means everywhere.
+//! - **shutdown** is this protocol's one verb — the only operation that *does*
+//!   something irreversible, and the reason the provider gates it by badge.
+//! - **the events** are pushes: the service `ipc_send`s each one to every
+//!   subscriber, no reply owed, so a slow or dead subscriber can never wedge the
+//!   source. **The kind is the packet's operation** — one declared event per
+//!   named kind, exactly as the input protocol delivers one per device class —
+//!   so a subscriber reads *what happened* out of the header instead of a tag
+//!   inside the payload. That is what the old `EventMessage`'s two leading bytes
+//!   (an operation byte saying "this is an event", then the kind) fold into.
+//!
+//! `Header.target` is unused (0) in both directions: the provider is the only
+//! object either side addresses. And no packet carries a version any more — the
+//! reserved `describe` verb is the version handshake, asked once at connect time
+//! rather than re-carried out of every packet's budget.
 
-/// The protocol version a client states nowhere yet — reserved for the day a
+const std = @import("std");
-/// handshake needs it; requests carry it so a mismatch can be refused loudly.
+const envelope = @import("envelope");
-pub const version: u16 = 1;
 
-pub const Operation = enum(u8) {
+/// What a published event carries beyond its kind. The kind is the packet's
-    /// Subscribe to power events: the subscriber's endpoint rides as the
+/// operation, so nothing here repeats it; `power_button`, `lid`, `ac` and
-    /// call's capability (the input/device-manager pattern); events arrive on
+/// `battery` leave both fields zero and are fully described by the verb alone.
-    /// it as buffered messages carrying an `EventMessage`.
+pub const Notice = extern struct {
-    subscribe = 1,
+    /// The device notification code (ACPI `Notify`'s second argument), or 0.
-    /// Orderly shutdown's last step: enter S5. Accepted only from PID 1
-    /// (init) — the process that has already run the stop sequence over
-    /// everything else.
-    shutdown = 2,
-    /// The published event payload (never sent *to* the service).
-    event = 3,
-};
-
-/// What happened. The vocabulary is hardware-neutral: a lid is a lid whether
-/// ACPI or a PSCI mailbox reported it.
-pub const Event = enum(u8) {
-    power_button = 1,
-    lid = 2,
-    ac = 3,
-    battery = 4,
-    /// A device notification that maps to none of the named events — the
-    /// `code` and `hid` fields say which device and what code.
-    notify = 5,
-};
-
-pub const Subscribe = extern struct {
-    operation: u8 = @intFromEnum(Operation.subscribe),
-    reserved0: u8 = 0,
-    version: u16 = version,
-    reserved1: u32 = 0,
-};
-
-pub const Shutdown = extern struct {
-    operation: u8 = @intFromEnum(Operation.shutdown),
-    reserved0: u8 = 0,
-    version: u16 = version,
-    reserved1: u32 = 0,
-};
-
-/// A published event, as the buffered-message payload subscribers receive.
-pub const EventMessage = extern struct {
-    operation: u8 = @intFromEnum(Operation.event),
-    /// An Event value.
-    event: u8,
-    reserved0: u16 = 0,
-    /// The device notification code (Notify's second argument), or 0.
     code: u32 = 0,
     /// The notifying device's hardware id (EISA-decoded), or all zero.
     hid: [8]u8 = .{0} ** 8,
 };
 
-pub const Reply = extern struct {
+pub const Protocol = envelope.Define(.{
-    status: i32,
+    .name = "power",
-    reserved: u32 = 0,
+    .version = 1,
-};
+    .operations = &.{
+        // Orderly shutdown's last step: enter S5. Honored only from a
+        // subscriber — init, the process that has already run the stop sequence
+        // over everything else (docs/os-development/power.md, "authority, not
+        // information"). Nothing to say and nothing to answer, so the verb and
+        // the reply's `Status` are the whole exchange.
+        .{ .name = "shutdown" },
+    },
+    .events = &.{
+        // The vocabulary is hardware-neutral: a lid is a lid whether ACPI or a
+        // PSCI mailbox reported it. One event per kind, each carrying the same
+        // `Notice`, because what differs between them is which thing happened —
+        // and that is the header's job now.
+        .{ .name = "power_button", .payload = Notice },
+        .{ .name = "lid", .payload = Notice },
+        .{ .name = "ac", .payload = Notice },
+        .{ .name = "battery", .payload = Notice },
+        // A device notification that maps to none of the named events — the
+        // `code` and `hid` say which device and what happened.
+        .{ .name = "notify", .payload = Notice },
+    },
+});
 
-/// Upper bound on any message in this protocol — sizes endpoint buffers.
+pub const Operation = Protocol.Operation;
-pub const message_maximum = 64;
+
+/// What happened. The event *is* the kind: this is the generated event
+/// enumeration, re-exported under the name this protocol has always called its
+/// vocabulary, with the same members it has always had.
+pub const Event = Protocol.Event;
+
+/// What a provider and a subscriber size their buffers to. This module used to
+/// declare 64 — the *push* floor — which was simply wrong for a protocol whose
+/// requests ride `ipc_call`: a provider sizing its receive buffer to 64 refuses
+/// any caller that sends up to the floor it is entitled to.
+pub const message_maximum: usize = Protocol.message_maximum;
+
+test "the kind is the verb, and an event fits the push floor" {
+    try std.testing.expectEqual(@as(u32, 16), @intFromEnum(Operation.shutdown));
+    try std.testing.expectEqual(@as(u32, 16), @intFromEnum(Event.power_button));
+    try std.testing.expectEqual(@as(u32, 17), @intFromEnum(Event.lid));
+    try std.testing.expectEqual(@as(u32, 18), @intFromEnum(Event.ac));
+    try std.testing.expectEqual(@as(u32, 19), @intFromEnum(Event.battery));
+    try std.testing.expectEqual(@as(u32, 20), @intFromEnum(Event.notify));
+    // subscribe is the RESERVED verb, below the protocol range entirely.
+    try std.testing.expectEqual(@as(u32, 2), envelope.operation_subscribe);
+    try std.testing.expectEqual(envelope.prefix_size + @sizeOf(Notice), Protocol.event_maximum);
+    try std.testing.expect(Protocol.event_maximum <= envelope.post_maximum);
+    // The call floor, not the push floor: `shutdown` is a synchronous call.
+    try std.testing.expectEqual(envelope.packet_maximum, message_maximum);
+}
+
+test "a pushed event names its kind in the header" {
+    var buffer: [envelope.post_maximum]u8 = undefined;
+    const packet = Protocol.encodeEvent(.power_button, 0, .{}, &buffer).?;
+    try std.testing.expectEqual(Event.power_button, Protocol.eventOf(packet).?);
+
+    const notified = Protocol.encodeEvent(.notify, 0, .{ .code = 0x80, .hid = "PNP0C0A\x00".* }, &buffer).?;
+    try std.testing.expectEqual(Event.notify, Protocol.eventOf(notified).?);
+    try std.testing.expectEqual(@as(u32, 0x80), Protocol.decodeEvent(.notify, notified).?.code);
+}

library/protocol/scanout/scanout-protocol.zig

@@ -1,49 +1,55 @@
 //! The scanout wire protocol — what the compositor says to a native scanout driver (e.g.
-//! virtio-gpu) over its well-known `.scanout` endpoint to put a composited frame on screen.
+//! virtio-gpu) over `/protocol/scanout` to put a composited frame on screen. The driver owns
-//! The driver owns the panel and the shared scanout surface it handed the compositor (via the
+//! the panel and the shared scanout surface it handed the compositor (via the display
-//! display service's `attach_scanout`); the compositor composites into that surface, then asks
+//! service's `attach_scanout`); the compositor composites into that surface, then asks the
-//! the driver to present a damaged rectangle. Tiny by design — one present request. Separate
+//! driver to present a damaged rectangle. Tiny by design — one present request. Separate from
-//! from the display protocol because the directions differ: clients call the compositor over
+//! the display protocol because the directions differ: clients call the compositor over
-//! `.display`; the compositor calls the driver over `.scanout`. See docs/display-v2.md.
+//! `/protocol/display`; the compositor calls the driver over `/protocol/scanout`. See
+//! docs/display-v2.md.
+//!
+//! One scanout per driver instance, so `Header.target` is always 0.
 
-const std = @import("std");
+const envelope = @import("envelope");
 
-pub const Operation = enum(u32) {
+/// `present(rect)`: put the given rectangle of the shared scanout surface on the panel (on
-    /// present(x, y, width, height): put the given rectangle of the shared scanout surface on
+/// virtio-gpu: transfer-to-host of the region, then a fenced resource flush).
-    /// the panel (on virtio-gpu: transfer-to-host of the region, then a fenced resource flush).
+pub const Present = extern struct {
-    present = 0,
-    /// get_modes() -> ModesReply: the display modes this scanout can switch to (V5).
-    get_modes = 1,
-    /// set_mode(width, height): change the scanout resolution — the shared surface is sized to
-    /// the largest mode, so this just re-points the scanout rectangle; the surface is unchanged.
-    set_mode = 2,
-};
-
-pub const Request = extern struct {
-    operation: u32,
     x: u32 = 0,
     y: u32 = 0,
     width: u32 = 0,
     height: u32 = 0,
 };
 
-pub const Reply = extern struct {
+/// `set_mode(width, height)`: change the scanout resolution — the shared surface is sized to
-    status: i32, // 0 on success, negative on failure
+/// the largest mode, so this just re-points the scanout rectangle; the surface is unchanged.
-    reserved: u32 = 0,
+pub const SetMode = extern struct { width: u32, height: u32 };
-};
 
 /// One offered display mode.
 pub const Mode = extern struct { width: u32, height: u32 };
 pub const max_modes = 4;
 
-/// The reply to `get_modes`: a small fixed list of modes.
+/// The answer to `get_modes`: a small fixed list of modes. The success/failure verdict is
-pub const ModesReply = extern struct {
+/// the reply's `Status`, so this carries only the modes.
-    status: i32,
+pub const Modes = extern struct {
-    count: u32,
+    count: u32 = 0,
-    modes: [max_modes]Mode,
+    _padding: u32 = 0,
+    modes: [max_modes]Mode = @splat(.{ .width = 0, .height = 0 }),
 };
 
-pub const message_maximum: usize = 64;
+pub const Protocol = envelope.Define(.{
-pub const request_size: usize = @sizeOf(Request);
+    .name = "scanout",
-pub const reply_size: usize = @sizeOf(Reply);
+    .version = 1,
-pub const modes_reply_size: usize = @sizeOf(ModesReply);
+    .operations = &.{
+        .{ .name = "present", .request = Present },
+        .{ .name = "get_modes", .reply = Modes },
+        .{ .name = "set_mode", .request = SetMode },
+    },
+});
+
+pub const Operation = Protocol.Operation;
+
+/// The call floor, like every synchronous protocol. This module used to declare
+/// 64 — the *push* floor — which was simply wrong: nothing here is pushed, and a
+/// provider sizing its receive buffer to 64 refuses (`-E2BIG`) any caller that
+/// sends up to the floor it is entitled to.
+pub const message_maximum: usize = Protocol.message_maximum;

library/protocol/usb-transfer/usb-transfer-protocol.zig

@@ -1,52 +1,66 @@
 //! The USB transfer protocol: what a USB class driver (a keyboard, mouse, or
-//! mass-storage driver) says to the xHCI bus driver over its well-known
+//! mass-storage driver) says to the xHCI bus driver over `/protocol/usb-transfer`
-//! `.usb_bus` endpoint to drive its device. The class driver owns no hardware —
+//! to drive its device. The class driver owns no hardware — it reaches its device
-//! it reaches its device entirely through these messages, the way a PS/2 keyboard
+//! entirely through these packets, the way a PS/2 keyboard driver reaches the
-//! driver reaches the 8042 through the ps2-bus. Extern-struct messages tagged by
+//! 8042 through the ps2-bus.
-//! `Operation`, the vfs-protocol / device-manager-protocol pattern.
+//!
+//! Defined through the envelope (docs/os-development/protocol-namespace.md), so
+//! every packet begins with the folded `Header`. **`Header.target` is the device
+//! token** — the per-open handle the bus driver hands back, which every request
+//! but `open` addressed through a `device_token` field of its own before the
+//! rebase. `open` itself addresses the *assigned device id*, because that is what
+//! the caller has before there is a token.
 //!
 //! The shape:
-//!   - **open** (a capability-passing `ipc.callCap`): the class driver hands over
+//!   - **open** (a capability-passing call): the class driver hands over its own
-//!     its own endpoint (for asynchronous interrupt reports) and its assigned
+//!     endpoint (for asynchronous interrupt reports); the target is its assigned
-//!     device id, and receives a `device_token` plus its interface's endpoints.
+//!     device id, and the reply carries a `device_token` plus its interface's
-//!   - **control / bulk** (synchronous `ipc.call`): one transfer, answered when
+//!     endpoints.
-//!     it completes. Control data travels inline (descriptors, HID/MSC class
+//!   - **control / bulk** (synchronous calls): one transfer, answered when it
-//!     requests are all small); bulk data travels by **physical address** — the
+//!     completes. Control data travels **in the packet's tail** in both
-//!     class driver's own `dma_alloc`'d buffer — so a 512-byte sector never has
+//!     directions (descriptors, HID/MSC class requests are all small), so the
-//!     to cross the 256-byte IPC boundary.
+//!     fixed parts stay tiny and `Status.len` is the transferred length — the
+//!     envelope's own field for "how many bytes follow", which is precisely what
+//!     the old `actual_length` said. Bulk data travels by **physical address** —
+//!     the class driver's own `dma_alloc`'d buffer — so a 512-byte sector never
+//!     has to cross the packet floor.
 //!   - **interrupt_subscribe** (synchronous): arm periodic IN polling of an
 //!     interrupt endpoint; each report the device produces is then pushed to the
-//!     class driver's endpoint as an asynchronous `InterruptReport` (`ipc.send`),
+//!     class driver's endpoint as an asynchronous `interrupt_report` event.
-//!     exactly how the input service delivers events.
+//!     It stays one of **this protocol's own verbs**, not the reserved
+//!     `subscribe`: the reserved verb means "push me this provider's events" and
+//!     carries the subscriber's endpoint, while this names one endpoint address
+//!     on one device and a poll length, and the endpoint it pushes to was handed
+//!     over at `open`. Same word, different contract.
+//!   - **dma_attach**: a class driver hands the controller a DMA-region
+//!     capability (riding the call's cap slot) so the controller binds that
+//!     buffer into its IOMMU domain and may then DMA to the physical addresses
+//!     inside it. Needed once per buffer the class driver will name in a `bulk`
+//!     transfer (its own, or one forwarded to it).
 //!
-//! Single controller assumption: one `.usb_bus` singleton serves QEMU's one xHCI.
+//! Single controller assumption: one provider serves QEMU's one xHCI. A
-//! A multi-controller machine would need a per-controller endpoint (the device
+//! multi-controller machine would need the controller in the target (or the
-//! manager handing each class driver the right one); noted, not built.
+//! spawner wiring each class driver its own channel); noted, not built.
 
-/// Fits one synchronous IPC message (kernel MESSAGE_MAXIMUM).
+const std = @import("std");
-pub const message_maximum: usize = 256;
+const envelope = @import("envelope");
 
-/// The largest inline control-transfer payload. Sized so a whole message
+/// The largest control-transfer data stage. It rides the packet's tail, so the
-/// (header + data) stays under `message_maximum`: descriptors and HID/MSC class
+/// bound is the call floor less the header and the fixed request part — derived
-/// requests are all far smaller.
+/// rather than declared, which is what keeps it honest when a field moves.
-pub const max_inline_data: usize = 200;
+pub const max_inline_data: usize = envelope.packet_maximum - envelope.prefix_size - @sizeOf(Control);
 
-/// The largest interrupt report pushed asynchronously. Sized so `InterruptReport`
+/// The largest interrupt report pushed asynchronously. An event packet is the
-/// fits an `ipc_send` payload slot (POST_MAXIMUM = 64): boot keyboard reports are
+/// header plus the payload within 64 bytes, so this is what is left after the
-/// 8 bytes, boot mouse reports 3–4.
+/// report's own four bytes of framing: boot keyboard reports are 8 bytes, boot
-pub const max_report_data: usize = 48;
+/// mouse reports 3–4, and the whole HID boot vocabulary fits many times over.
+/// A device that produces more has its report truncated, never split.
+pub const max_report_data: usize = 40;
 
 /// Endpoints per interface reported back in an open reply (a boot HID interface
 /// has one interrupt endpoint, a mass-storage interface two bulk endpoints).
 pub const max_reported_endpoints: usize = 4;
 
-pub const Operation = enum(u32) {
-    open = 0,
-    control = 1,
-    interrupt_subscribe = 2,
-    bulk = 3,
-};
-
 /// The endpoint facts a class driver needs, lifted from the endpoint descriptor
 /// the bus driver already parsed during enumeration.
 pub const Endpoint = extern struct {
@@ -59,101 +73,146 @@ pub const Endpoint = extern struct {
     reserved: [3]u8 = .{ 0, 0, 0 },
 };
 
-/// open: the class driver's receive endpoint rides as the call's capability, and
+// --- the per-operation request and reply parts ------------------------------
-/// `device_id` is the interface's assigned id (its argv[1]).
+//
-pub const OpenRequest = extern struct {
+// Each names the bytes AFTER the prefix. Nothing here carries an operation or a
-    operation: u32 = @intFromEnum(Operation.open),
+// device token: those are the packet header's, folded in once. No reply carries
-    reserved: u32 = 0,
+// a status either — that is the `Status` every reply begins with.
-    device_id: u64,
-};
 
-/// The answer to open: a token scoping every later request to this device, the
+/// The answer to `open`: the token every later packet puts in `Header.target`,
-/// interface's class triple (a sanity check), and its endpoints.
+/// the interface's class triple (a sanity check), and its endpoints.
-pub const OpenReply = extern struct {
+pub const Opened = extern struct {
-    status: i32,
-    endpoint_count: u32,
     device_token: u64,
+    endpoint_count: u32,
     interface_class: u8,
     interface_subclass: u8,
     interface_protocol: u8,
     interface_number: u8,
-    reserved2: u32 = 0,
     endpoints: [max_reported_endpoints]Endpoint = [_]Endpoint{.{ .address = 0, .transfer_type = 0, .max_packet_size = 0, .interval = 0 }} ** max_reported_endpoints,
 };
 
-/// control: one EP0 control transfer. `setup` is a bit-cast `usb_abi.Request`.
+/// `control`: one EP0 control transfer on `Header.target`. `setup` is a bit-cast
-/// For an OUT transfer `data[0..data_length]` is sent; for an IN transfer the
+/// `usb_abi.Request`. For an OUT transfer the data stage is the request's tail;
-/// reply carries up to `data_length` bytes back.
+/// for an IN transfer it comes back as the reply's tail, and `Status.len` is how
-pub const ControlRequest = extern struct {
+/// much of it arrived.
-    operation: u32 = @intFromEnum(Operation.control),
+pub const Control = extern struct {
-    reserved: u32 = 0,
-    device_token: u64,
     setup: [8]u8,
-    direction_in: u8, // 1 = device-to-host (IN), 0 = host-to-device (OUT)
+    /// 1 = device-to-host (IN), 0 = host-to-device (OUT).
-    reserved2: u8 = 0,
+    direction_in: u8,
+    _padding: u8 = 0,
+    /// Bytes of data stage: what an IN transfer asks for, and what an OUT
+    /// transfer's tail carries.
     data_length: u16,
-    reserved3: u32 = 0,
+    _padding2: u32 = 0,
-    data: [max_inline_data]u8 = [_]u8{0} ** max_inline_data,
 };
 
-pub const ControlReply = extern struct {
+/// `interrupt_subscribe`: begin periodic IN polling of an interrupt endpoint of
-    status: i32, // 0 success, negative on failure/stall
+/// `Header.target`. Each report the device returns is pushed to the endpoint the
-    actual_length: u32,
+/// caller handed over at `open`, as an `interrupt_report` event.
-    data: [max_inline_data]u8 = [_]u8{0} ** max_inline_data,
+pub const InterruptSubscribe = extern struct {
-};
-
-/// interrupt_subscribe: begin periodic IN polling of an interrupt endpoint. Each
-/// report the device returns is pushed to the caller's endpoint (handed over at
-/// open) as an asynchronous `InterruptReport`.
-pub const InterruptSubscribeRequest = extern struct {
-    operation: u32 = @intFromEnum(Operation.interrupt_subscribe),
-    reserved: u32 = 0,
-    device_token: u64,
     endpoint_address: u8,
-    reserved2: u8 = 0,
+    _padding: u8 = 0,
-    max_length: u16, // bytes to request per poll (the endpoint's max packet size)
+    /// Bytes to request per poll (the endpoint's max packet size).
+    max_length: u16,
 };
 
-pub const InterruptSubscribeReply = extern struct {
+/// `bulk`: one bulk IN or OUT transfer on `Header.target`. `physical_address` is
-    status: i32,
+/// the class driver's own `dma_alloc`'d buffer — the controller DMAs straight
-    reserved: u32 = 0,
+/// to/from it, so the bulk data never crosses IPC. `endpoint_address`'s bit 7
-};
+/// selects IN vs OUT.
-
+pub const Bulk = extern struct {
-/// bulk: one bulk IN or OUT transfer. `physical_address` is the class driver's own
-/// `dma_alloc`'d buffer — the controller DMAs straight to/from it, so the bulk
-/// data never crosses IPC. `endpoint_address`'s bit 7 selects IN vs OUT.
-pub const BulkRequest = extern struct {
-    operation: u32 = @intFromEnum(Operation.bulk),
-    reserved: u32 = 0,
-    device_token: u64,
     physical_address: u64,
     length: u32,
     endpoint_address: u8,
-    reserved2: u8 = 0,
+    _padding: u8 = 0,
-    reserved3: u16 = 0,
+    _padding2: u16 = 0,
 };
 
-pub const BulkReply = extern struct {
+/// How many bytes a bulk transfer actually moved. It cannot ride `Status.len`
-    status: i32,
+/// the way a control transfer's does: nothing follows a bulk reply, because the
-    actual_length: u32,
+/// data went to the caller's DMA buffer rather than into the packet.
-};
+pub const Transferred = extern struct { actual_length: u32 };
 
-/// An asynchronous interrupt report, pushed with `ipc.send` to a subscriber's
+/// One asynchronous interrupt report, pushed to the endpoint the class driver
-/// endpoint. `Received.isMessage()` is set; there is no reply owed.
+/// handed over at `open`. The device it came from is `Header.target`.
 pub const InterruptReport = extern struct {
-    device_token: u64,
     endpoint_address: u8,
     length: u8,
-    reserved: u16 = 0,
+    _padding: u16 = 0,
     data: [max_report_data]u8 = [_]u8{0} ** max_report_data,
 };
 
-comptime {
+pub const Protocol = envelope.Define(.{
-    const std = @import("std");
+    .name = "usb-transfer",
-    // Every synchronous message must fit one IPC message; the async report must
+    .version = 1,
-    // fit an ipc_send payload slot.
+    .operations = &.{
-    std.debug.assert(@sizeOf(ControlRequest) <= message_maximum);
+        // open: the target is the interface's assigned device id (its argv[1]),
-    std.debug.assert(@sizeOf(ControlReply) <= message_maximum);
+        // and the class driver's receive endpoint rides as the capability.
-    std.debug.assert(@sizeOf(OpenReply) <= message_maximum);
+        .{ .name = "open", .reply = Opened },
-    std.debug.assert(@sizeOf(InterruptReport) <= 64);
+        .{ .name = "control", .request = Control },
+        .{ .name = "interrupt_subscribe", .request = InterruptSubscribe },
+        .{ .name = "bulk", .request = Bulk, .reply = Transferred },
+        // dma_attach: the region capability rides the call's cap slot; the
+        // target says which caller's device is attaching, so there is nothing
+        // left for a body to carry.
+        .{ .name = "dma_attach" },
+    },
+    .events = &.{
+        .{ .name = "interrupt_report", .payload = InterruptReport },
+    },
+});
+
+pub const Operation = Protocol.Operation;
+pub const Event = Protocol.Event;
+
+/// What both sides size their buffers to — the call floor, as every protocol does.
+pub const message_maximum: usize = Protocol.message_maximum;
+
+test "the budgets, re-verified by Define rather than by hand" {
+    // What the hand-rolled comptime asserts used to say, now said by `Define`
+    // — and counting the header, which the old checks did not.
+    try std.testing.expectEqual(@as(usize, 224), max_inline_data);
+    try std.testing.expect(Protocol.request_maximum <= envelope.packet_maximum);
+    try std.testing.expect(Protocol.reply_maximum <= envelope.packet_maximum);
+    // The report was 48 bytes of data in a 64-byte struct that had no room left
+    // for a header. Folding the device token into the target and trimming the
+    // data to 40 leaves the whole packet at 60 of the 64-byte push floor.
+    try std.testing.expectEqual(@as(usize, 44), @sizeOf(InterruptReport));
+    try std.testing.expectEqual(@as(usize, 60), Protocol.event_maximum);
+    try std.testing.expect(Protocol.event_maximum <= envelope.post_maximum);
+}
+
+test "the verb numbering, and the device token in the header" {
+    try std.testing.expectEqual(@as(u32, 16), @intFromEnum(Operation.open));
+    try std.testing.expectEqual(@as(u32, 17), @intFromEnum(Operation.control));
+    try std.testing.expectEqual(@as(u32, 18), @intFromEnum(Operation.interrupt_subscribe));
+    try std.testing.expectEqual(@as(u32, 19), @intFromEnum(Operation.bulk));
+    try std.testing.expectEqual(@as(u32, 20), @intFromEnum(Operation.dma_attach));
+    try std.testing.expectEqual(@as(u32, 16), @intFromEnum(Event.interrupt_report));
+
+    var buffer: [message_maximum]u8 = undefined;
+    const packet = Protocol.encodeRequest(.control, 9, .{
+        .setup = .{ 0, 6, 0, 1, 0, 0, 18, 0 },
+        .direction_in = 1,
+        .data_length = 18,
+    }, &.{}, &buffer).?;
+    try std.testing.expectEqual(@as(u64, 9), envelope.headerOf(packet).?.target);
+    try std.testing.expectEqual(@as(u16, 18), Protocol.decodeRequest(.control, packet).?.data_length);
+}
+
+test "a control OUT carries its data stage as the packet's tail" {
+    var buffer: [message_maximum]u8 = undefined;
+    const payload = [_]u8{ 1, 2, 3, 4 };
+    const packet = Protocol.encodeRequest(.control, 5, .{
+        .setup = .{ 0x21, 11, 0, 0, 0, 0, 4, 0 },
+        .direction_in = 0,
+        .data_length = payload.len,
+    }, &payload, &buffer).?;
+    try std.testing.expectEqualSlices(u8, &payload, Protocol.requestTail(.control, packet));
+
+    // And the answer to an IN: the bytes follow the (empty) fixed reply part,
+    // with `Status.len` counting exactly them.
+    const answered = Protocol.encodeReply(.control, 0, {}, &payload, &buffer).?;
+    try std.testing.expectEqual(@as(u32, payload.len), envelope.statusOf(answered).?.len);
+    try std.testing.expectEqualSlices(u8, &payload, Protocol.replyTail(.control, answered));
 }

library/protocol/vfs/vfs-protocol.zig

@@ -1,40 +1,30 @@
-//! The VFS wire protocol — the message format spoken between a client (via the file
+//! The VFS wire protocol — what a client (through the file API,
-//! API) and the user-space VFS server over IPC. A request is a fixed `Request` header
+//! library/kernel/file-system.zig) says to a filesystem backend over IPC. Defined
-//! followed by an inline payload (a path, or write bytes); a reply is a fixed `Reply`
+//! through the envelope (docs/os-development/protocol-namespace.md), so every
-//! header followed by an inline payload (read bytes, or a FileStatus). Everything fits
+//! packet begins with the folded `Header`: the verb in `Header.operation`, and
-//! in one IPC message (<= ipc MESSAGE_MAXIMUM = 256 bytes).
+//! **the open node id in `Header.target`** — the field that used to be
+//! `Request.node`. A path appears in the conversation once, at `open`; every
+//! packet after it addresses that integer.
 //!
-//! This is a danos-native contract, so it uses danos names throughout. The client
+//! This is a danos-native contract, so it uses danos names throughout. It is
-//! side is `runtime.fs` (library/runtime/fs.zig), which programs use directly.
+//! user-space only — the kernel knows nothing of files or paths; it only routes
+//! (`fs_resolve`) and moves the bytes. The backends that serve it today are the
+//! FAT server (system/services/fat/) and the protocol registry inside PID 1
+//! (system/services/init/), which is a *synthetic* backend: `/protocol` holds
+//! contracts rather than files.
 //!
-//! This is user-space only — the kernel knows nothing of files or paths; it only moves the bytes.
+//! **An `open` reply may carry a capability.** The `open` request rides
-//! Shared by library/runtime/fs.zig (the client) and the mount backends that serve it (today
+//! `ipc_call`, and the reply direction of a call can hand back an endpoint
-//! the fat server, system/services/fat/). The standalone user-space VFS server it was first
+//! (`ipc.callCap`'s `Reply.cap`). A file backend never uses it — FAT answers with
-//! written against has retired — path routing moved into the kernel (system/kernel/vfs.zig,
+//! a node id and nothing else — but the registry does: opening a
-//! fs_resolve) — but the protocol module outlived it.
+//! `NodeKind.protocol` node under `/protocol` returns the provider's endpoint,
+//! which is the channel. The convention is per-backend, not per-operation: a
+//! client that did not ask a synthetic backend simply gets no capability back.
 
-pub const Operation = enum(u32) {
+const envelope = @import("envelope");
-    open, // open(path) -> node id
-    close, // close(node)
-    read, // read(node, offset, len) -> bytes
-    write, // write(node, offset, bytes) -> count
-    status, // status(node) -> FileStatus
-    // Appended for the mount router (M5). Values stay stable, so existing clients
-    // and the flat-ramfs tests are unaffected.
-    readdir, // readdir(dir_node, cursor=offset) -> one DirectoryEntry (len==0 => EOF)
-    mount, // mount(prefix payload, capability = backend endpoint)
-    unmount, // unmount(prefix payload)
-    // Appended for filesystem mutation (Phase 2). Path-based (the path is the
-    // payload); a mounted backend handles them, the flat ramfs refuses them.
-    mkdir, // mkdir(path payload) -> status
-    unlink, // unlink(path payload) -> status
-    // rename: the payload is the old path, a single 0x00 separator, then the new
-    // path. Same-directory rename only (the router requires both under one mount).
-    rename, // rename(old\0new payload) -> status
-};
 
-/// The type of a filesystem node, aligned to the FSH file-type table
+/// The type of a filesystem node, aligned to the node-kind table
-/// (docs/danos-file-system-hierarchy-FSH.md). Fills `FileStatus.kind` and
+/// (docs/file-system-development/file-system-hierarchy.md). Fills `FileStatus.kind` and
 /// `DirectoryEntry.kind`; `regular = 0` keeps the historical hardcoded value.
 pub const NodeKind = enum(u32) {
     regular = 0,
@@ -44,40 +34,26 @@ pub const NodeKind = enum(u32) {
     symbolic_link = 4,
     fifo = 5,
     socket = 6,
+    /// A node that names a *contract*, not a file: opening it establishes a
+    /// channel to whatever process currently provides that protocol, delivered
+    /// as an endpoint capability in the reply rather than a node id. This is
+    /// what lives under `/protocol`; `readdir` lists these like any other node,
+    /// so the tree stays browsable for diagnosis.
+    protocol = 7,
 };
 
-/// One directory entry, returned by `readdir`: a fixed header followed inline in
+/// One directory entry: the fixed part of a `readdir` reply, followed inline by
-/// the reply payload by `name_len` bytes of name. A zero-length reply is EOF.
+/// `name_len` bytes of name. **A zero `name_len` is end of directory** — the
+/// reply's own length cannot say so any more, because the envelope always sends
+/// the fixed part.
 pub const DirectoryEntry = extern struct {
-    kind: u32, // a NodeKind
+    kind: u32 = 0, // a NodeKind
-    name_len: u32,
+    name_len: u32 = 0,
-    size: u64,
+    size: u64 = 0,
 };
 
 pub const directory_entry_size: usize = @sizeOf(DirectoryEntry);
 
-/// Request header. `node` is the server-side open-file id (from a prior open);
-/// for `open` the path is the payload and `len` is its length. `offset`/`len`
-/// carry the read/write position and count.
-pub const Request = extern struct {
-    operation: Operation,
-    node: u64,
-    offset: u64,
-    len: u32,
-    flags: u32,
-};
-
-/// Reply header. `status` is 0 on success or a negative errno; `node` is the new
-/// open-file id (for `open`); `len` is the payload length (bytes read, or the
-/// FileStatus size).
-pub const Reply = extern struct {
-    status: i32,
-    _padding: u32 = 0,
-    node: u64 = 0,
-    len: u32 = 0,
-    _padding2: u32 = 0,
-};
-
 /// A file's metadata (the danos-native answer to a `status` request). The POSIX
 /// layer maps this onto `struct stat`.
 pub const FileStatus = extern struct {
@@ -89,13 +65,84 @@ pub const FileStatus = extern struct {
     mtime: u64 = 0,
 };
 
-pub const message_maximum: usize = 256;
+// --- the per-operation request and reply parts ------------------------------
-pub const request_size: usize = @sizeOf(Request);
+//
-pub const reply_size: usize = @sizeOf(Reply);
+// Each names the bytes AFTER the prefix. Nothing here carries an operation or a
-/// Largest inline payload that still fits one IPC message alongside a header.
+// node id: those are the packet header's, folded in once.
-pub const maximum_payload: usize = message_maximum - request_size;
 
-/// Open flags (danos-native; `runtime.fs.OpenOptions` maps its booleans onto these).
+/// `open(flags)` with the path as the packet's tail. The one verb that spends a
+/// path; everything after it addresses the node id this returns.
+pub const Open = extern struct { flags: u32 = 0 };
+
+/// The node id an `open` established — the integer every later packet puts in
+/// `Header.target`. Meaningful only between this client and this backend.
+pub const Opened = extern struct { node: u64 };
+
+/// `read(offset, len)` on `Header.target`; the bytes come back as the reply tail.
+pub const Read = extern struct {
+    offset: u64,
+    len: u32,
+    _padding: u32 = 0,
+};
+
+/// `write(offset, len)` on `Header.target`, with the data as the packet's tail.
+pub const Write = extern struct {
+    offset: u64,
+    len: u32,
+    _padding: u32 = 0,
+};
+
+/// How many bytes a `write` actually took — it may be short.
+pub const Written = extern struct { count: u32 };
+
+/// `readdir(cursor)` on `Header.target`: one entry per call, cursor-advanced.
+pub const Readdir = extern struct { cursor: u64 };
+
+/// The contract, whole. Verbs number from `envelope.first_protocol_operation`
+/// (16) in this order; the reserved verbs below it mean what they mean
+/// everywhere. `readdir` stays a protocol verb rather than folding into the
+/// reserved `enumerate`: it enumerates the children of one *node*, where
+/// `enumerate` names a provider's targets.
+pub const Protocol = envelope.Define(.{
+    .name = "vfs",
+    .version = 1,
+    .operations = &.{
+        .{ .name = "open", .request = Open, .reply = Opened },
+        .{ .name = "close" },
+        .{ .name = "read", .request = Read },
+        .{ .name = "write", .request = Write, .reply = Written },
+        .{ .name = "status", .reply = FileStatus },
+        .{ .name = "readdir", .request = Readdir, .reply = DirectoryEntry },
+        // The mount router's two verbs. Path routing lives in the kernel now
+        // (system/kernel/vfs.zig), so no backend implements either; they keep
+        // their numbers so the vocabulary stays the one docs/vfs-protocol.md
+        // describes.
+        .{ .name = "mount" }, // tail = the prefix, capability = the backend's endpoint
+        .{ .name = "unmount" }, // tail = the prefix
+        // Filesystem mutation, path-based: the path is the packet's tail.
+        .{ .name = "mkdir" },
+        .{ .name = "unlink" },
+        // rename: the tail is the old path, a single 0x00 separator, then the
+        // new path. Same-directory rename only.
+        .{ .name = "rename" },
+        // The registry's claim verb (P2): the name is the tail and the
+        // provider's endpoint rides the call as its capability. A file backend
+        // refuses it; only init implements it.
+        .{ .name = "bind" },
+    },
+});
+
+pub const Operation = Protocol.Operation;
+
+/// What a backend sizes its buffers to — the call floor, as every protocol does.
+pub const message_maximum: usize = Protocol.message_maximum;
+
+/// The most inline payload any request may carry: the floor less the header and
+/// the widest fixed request part, so one bound serves every verb (a path, write
+/// data, a read's answer).
+pub const maximum_payload: usize = envelope.packet_maximum - Protocol.request_maximum;
+
+/// Open flags (danos-native; `file_system.OpenOptions` maps its booleans onto these).
 pub const create: u32 = 1;
 /// Open a directory (for readdir) rather than a file. A mounted backend uses
 /// this to open a directory node; the flat ramfs ignores it.
@@ -105,13 +152,42 @@ pub const directory: u32 = 2;
 /// backend frees the old cluster chain; the flat ramfs ignores it.
 pub const truncate: u32 = 4;
 
-test "protocol struct sizes and node kinds" {
+test "the stable wire values: node kinds, entry layout, and the verb numbering" {
     const std = @import("std");
     try std.testing.expectEqual(@as(u32, 0), @intFromEnum(NodeKind.regular));
     try std.testing.expectEqual(@as(u32, 1), @intFromEnum(NodeKind.directory));
+    // Appended with the protocol namespace; every earlier value keeps its own.
+    try std.testing.expectEqual(@as(u32, 6), @intFromEnum(NodeKind.socket));
+    try std.testing.expectEqual(@as(u32, 7), @intFromEnum(NodeKind.protocol));
     try std.testing.expectEqual(@as(usize, 16), @sizeOf(DirectoryEntry));
-    // The appended operations keep the original values.
+
-    try std.testing.expectEqual(@as(u32, 0), @intFromEnum(Operation.open));
+    // The numbering the envelope gives this protocol. These are NEW values: the
-    try std.testing.expectEqual(@as(u32, 4), @intFromEnum(Operation.status));
+    // rebase moved every verb above the reserved range, so the old 0..11 are
-    try std.testing.expectEqual(@as(u32, 5), @intFromEnum(Operation.readdir));
+    // gone and 16..27 are what the wire carries. Pinned because both sides of a
+    // flag-day have to agree on them, not because they may never change again.
+    try std.testing.expectEqual(@as(u32, 16), @intFromEnum(Operation.open));
+    try std.testing.expectEqual(@as(u32, 17), @intFromEnum(Operation.close));
+    try std.testing.expectEqual(@as(u32, 18), @intFromEnum(Operation.read));
+    try std.testing.expectEqual(@as(u32, 19), @intFromEnum(Operation.write));
+    try std.testing.expectEqual(@as(u32, 20), @intFromEnum(Operation.status));
+    try std.testing.expectEqual(@as(u32, 21), @intFromEnum(Operation.readdir));
+    try std.testing.expectEqual(@as(u32, 26), @intFromEnum(Operation.rename));
+    try std.testing.expectEqual(@as(u32, 27), @intFromEnum(Operation.bind));
+    // The payload bound is what it always was, arrived at the other way round:
+    // the header plus the widest fixed request part is 32 bytes of the floor.
+    try std.testing.expectEqual(@as(usize, 224), maximum_payload);
+}
+
+test "the node id rides the header, and a path rides the tail" {
+    const std = @import("std");
+    var buffer: [message_maximum]u8 = undefined;
+
+    const opening = Protocol.encodeRequest(.open, 0, .{ .flags = create }, "/a/b", &buffer).?;
+    try std.testing.expectEqual(@as(u32, create), Protocol.decodeRequest(.open, opening).?.flags);
+    try std.testing.expectEqualStrings("/a/b", Protocol.requestTail(.open, opening));
+    try std.testing.expectEqual(@as(u64, 0), envelope.headerOf(opening).?.target);
+
+    const reading = Protocol.encodeRequest(.read, 7, .{ .offset = 512, .len = 64 }, &.{}, &buffer).?;
+    try std.testing.expectEqual(@as(u64, 7), envelope.headerOf(reading).?.target);
+    try std.testing.expectEqual(@as(u64, 512), Protocol.decodeRequest(.read, reading).?.offset);
 }

library/xkeyboard-config/build.zig

@@ -0,0 +1,31 @@
+//! The "xkeyboard-config" library domain: keyboard layouts compiled from the
+//! X11 xkeyboard-config database into native Zig (keycode + modifiers ->
+//! keysym/character). The `layouts` tables are generated by
+//! tools/make-xkeyboard-config.py; `xkeyboard-config` is the hand-written API
+//! over them.
+
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    const layouts = b.addModule("layouts", .{
+        .root_source_file = b.path("generated/layouts.zig"),
+    });
+    _ = b.addModule("xkeyboard-config", .{
+        .root_source_file = b.path("xkeyboard-config.zig"),
+        .imports = &.{.{ .name = "layouts", .module = layouts }},
+    });
+
+    // Standalone `zig build test` for this domain alone; the root build keeps
+    // its aggregate test step. The keycode->character assertions are the
+    // end-to-end proof that the xkb-data -> generator -> Zig-lookup pipeline
+    // is correct.
+    const test_step = b.step("test", "Run the xkeyboard-config unit tests");
+    const xkb_tests = b.addTest(.{
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("xkeyboard-config.zig"),
+            .target = b.resolveTargetQuery(.{}),
+            .imports = &.{.{ .name = "layouts", .module = layouts }},
+        }),
+    });
+    test_step.dependOn(&b.addRunArtifact(xkb_tests).step);
+}

library/xkeyboard-config/build.zig.zon

@@ -0,0 +1,8 @@
+.{
+    .name = .xkeyboard_config,
+    .version = "0.0.0",
+    .fingerprint = 0xea5abe82f08b6eae, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{},
+    .paths = .{""},
+}

system/abi.zig

@@ -1,6 +1,6 @@
 //! The **private kernel ↔ runtime** ABI: the raw system_call contract — the call
 //! numbers, `mmap` protection flags, the page size those calls work in, and the IPC
-//! name-registry ids and notification bit. Shared by the kernel dispatcher
+//! notification bits. Shared by the kernel dispatcher
 //! (system/kernel/process.zig) and the user-space runtime library (library/runtime/),
 //! so the two can never drift.
 //!
@@ -33,8 +33,13 @@ pub const SystemCall = enum(u64) {
     mmap = 4, // mmap(len, prot) -> base: grant zeroed, page-aligned user pages
     munmap = 5, // munmap(base, len): release pages from a prior mmap
     create_ipc_endpoint = 6, // create_ipc_endpoint() -> handle: a new IPC endpoint
-    ipc_register = 7, // ipc_register(service_id, handle): publish an endpoint by well-known id
+    // 7 and 8 were ipc_register/ipc_lookup — the flat ServiceId name registry,
-    ipc_lookup = 8, // ipc_lookup(service_id) -> handle: find a published endpoint
+    // retired with the protocol namespace (docs/os-development/protocol-namespace.md).
+    // A service now binds its name at the registry (init, over /protocol) and a
+    // client resolves and opens that path; neither is a system call any more. The
+    // numbers stay vacant rather than being reused: every other entry is
+    // position-fixed by an explicit value, so a hole costs nothing and a reused
+    // number would silently mean two things across a rebuild boundary.
     ipc_call = 9, // ipc_call(h, message, len, reply, cap) -> reply_len: send + block for reply
     ipc_reply_wait = 10, // ipc_reply_wait(h, reply, len, receive, cap) -> receive_len (+badge in rdx)
     device_enumerate = 11, // device_enumerate(buffer, maximum) -> count: snapshot the device table
@@ -76,6 +81,10 @@ pub const SystemCall = enum(u64) {
     fs_node = 47, // fs_node(op, node_token, offset, buf_ptr, buf_len) -> bytes/0/-errno: read/status/readdir on a kernel-served node (op values mirror the vfs-protocol Operation numbers)
     fs_mount = 48, // fs_mount(prefix_ptr, prefix_len, backend_handle, rewrite_ptr, rewrite_len) -> 0/-errno: mount a userspace filesystem's endpoint at an absolute prefix (possession of the handle is the capability)
     fs_unmount = 49, // fs_unmount(prefix_ptr, prefix_len) -> 0/-errno: remove a backend mount
+    iommu_fault_drain = 50, // iommu_fault_drain() -> count: drain + log pending IOMMU translation faults (a diagnostic; the count of faults seen this call)
+    dma_bind = 51, // dma_bind(device_id, region_handle) -> 0/-errno: map a DMA-region capability into the claimed device's IOMMU domain (idempotent). The caller must own the device and hold the handle
+    dma_unbind = 52, // dma_unbind(device_id, region_handle) -> 0/-errno: unmap a previously bound region from the device's domain and invalidate
+    handle_close = 53, // handle_close(handle) -> 0/-errno: drop one capability handle and free its table slot (endpoints, shared-memory, DMA regions)
     _,
 };
 
@@ -113,6 +122,7 @@ pub const msi_address_base: u64 = 0xFEE0_0000;
 pub const dma_coherent: u64 = 1; // strong-uncacheable — the default, the only portable one
 pub const dma_write_combining: u64 = 2; // write-combining (framebuffers); needs PAT
 pub const dma_below_4g: u64 = 4; // physical address must fit 32 bits (legacy DMA engines)
+pub const dma_shareable: u64 = 8; // return a capability handle (r8) so the region can be delegated + dma_bound
 
 /// Set in the badge returned by `ipc_reply_wait` when what arrived is an
 /// **asynchronous notification** (a device interrupt bound with `irq_bind`, or a
@@ -242,8 +252,11 @@ pub const klog_maximum_message: usize = 256;
 pub const fs_route_kernel: u64 = 0; // rdx = node token; serve via fs_node
 pub const fs_route_backend: u64 = 1; // rdx = endpoint handle; speak vfs-protocol
 
-/// fs_node operations — the same numbers as the vfs-protocol Operation enum, so
+/// fs_node operations. These were once the vfs-protocol Operation numbers; the
-/// client code shares one vocabulary.
+/// rebase onto the envelope moved every protocol verb above the reserved range
+/// (16 and up), and these did not follow — they are a *syscall* selector, not a
+/// packet's verb, and renumbering a kernel ABI to track a wire format would be
+/// coupling in the wrong direction. The two vocabularies are simply separate now.
 pub const fs_node_read: u64 = 2;
 pub const fs_node_status: u64 = 4;
 pub const fs_node_readdir: u64 = 5;
@@ -279,23 +292,11 @@ pub const KlogStatus = extern struct {
     boot_unix_seconds: u64, // wall-clock time of boot (RTC anchor)
 };
 
-/// Well-known IPC service ids for the bootstrap name registry (create_ipc_endpoint +
+// The `ServiceId` enum lived here: a flat, compile-time list of well-known
-/// ipc_register/ipc_lookup). Small integers, so no string interning is needed
+// service ids backed by a 16-slot kernel table. It is gone with the protocol
-/// during bring-up. The VFS server registers under `vfs`; clients look it up.
+// namespace — names are strings resolved under `/protocol` at run time, so a
-pub const ServiceId = enum(u32) {
+// third-party program can introduce a contract the ABI never heard of, and the
-    vfs = 1, // RETIRED: the router moved into the kernel (fs_resolve); the slot stays reserved
+// registrar (init) decides who may claim one.
-    input = 2,
-    ps2_bus = 3, // the 8042 owner; child device drivers attach here for raw bytes
-    device_manager = 4, // the tree, the matcher, the supervisor (docs/device-manager.md)
-    power = 5, // system power: events (button, lid, battery) + shutdown (docs/power.md; domain-named per docs/discovery.md — the acpi service registers it on x86, a PSCI service will on ARM)
-    usb_bus = 6, // the xHCI host-controller driver's transfer endpoint; USB class drivers look it up and `callCap`-open their device to get a private per-device transfer channel (docs/driver-model.md)
-    block = 7, // a block-device driver (USB mass storage today): read/write of fixed-size blocks, the storage a filesystem sits on
-    fat = 8, // the FAT filesystem server; the VFS mounts it and forwards paths under its mount point (/mnt/usb) to it
-    display = 9, // the display service: owns the framebuffer, composites a layer stack, presents frames (docs/display.md)
-    shared_memory_test = 10, // the shared-memory test server (V2): a client passes it a shared-memory capability, it maps + verifies (docs/display-v2.md)
-    scanout = 11, // a native scanout driver (virtio-gpu): the compositor finds it here to upgrade off the GOP framebuffer (docs/display-v2.md)
-    _,
-};
 
 /// Protection flags for `mmap` (matching the usual C bit values).
 pub const prot_read: u64 = 1;

system/configuration/devices.csv

@@ -1,4 +1,4 @@
-# /etc/devices.csv — the device→driver registry.
+# /system/configuration/devices.csv — the device→driver registry.
 #
 # The device manager reads this at boot and binds each device a bus driver
 # reports to the driver named here. It is AUTHORITATIVE: a device that no row

system/configuration/init-diagnose.csv

@@ -1,9 +1,10 @@
-# /etc/init.csv — diagnose variant (-Ddiagnose), bundled at /etc/init.csv.
+# /system/configuration/init.csv — diagnose variant (-Ddiagnose), bundled at
+# /system/configuration/init.csv.
 #
 # The display stack (display, display-demo) is omitted so the kernel's timestamped
 # on-screen boot transcript is never suppressed — the bring-up timeline (USB,
-# storage, logger) stays readable on real hardware with no serial. See etc/init.csv
+# storage, logger) stays readable on real hardware with no serial. See
-# for the format; this file must otherwise track it.
+# system/configuration/init.csv for the format; this file must otherwise track it.
 #
 # service                          args...
 /system/services/input

system/configuration/init.csv

@@ -1,4 +1,4 @@
-# /etc/init.csv — the services init (PID 1) starts at boot, in order.
+# /system/configuration/init.csv — the services init (PID 1) starts at boot, in order.
 #
 # init reads this at startup and spawns each service supervised (restarting it on
 # a crash, up to a cap). Startup order is top->bottom; shutdown is the reverse, so
@@ -9,7 +9,7 @@
 # '#' starts a comment (whole-line or trailing); blank lines are ignored. The
 # first field is the service binary path; any fields after it are the service's
 # argv. Drivers are absent on purpose — the device manager discovers hardware and
-# spawns those (see /etc/devices.csv).
+# spawns those (see /system/configuration/devices.csv).
 #
 # service                          args...
 /system/services/input

system/configuration/protocol.csv

@@ -0,0 +1,175 @@
+# /system/configuration/protocol.csv — who may claim, and who may reach, a name
+# under /protocol (docs/os-development/protocol-namespace.md).
+#
+# init is the registrar: it serves /protocol, and every bind AND every open is
+# checked against this file. It is AUTHORITATIVE — a name no row grants cannot be
+# bound or reached, and a missing file means nothing may be bound or reached at
+# all.
+#
+# A refused open is answered exactly as a name nobody bound is: -ENOENT, and no
+# capability. That is not politeness, it is the model — the namespace IS the
+# restriction, so what a process may not open simply does not exist for it, and
+# there is no "permission denied" for it to tell apart from "no such contract".
+# Which is why a missing row here shows up as a client retrying forever rather
+# than as an error: check this file first, and `readdir /protocol` second.
+#
+# '#' starts a comment (whole-line or trailing); blank lines are ignored.
+# Whitespace around a field is trimmed, so columns may be padded. Four
+# comma-separated fields per row:
+#
+#   binary      the claimant's binary path, exactly as the kernel stamped it at
+#               spawn (argv[0]) — unforgeable, read from the process records
+#   supervisor  the authorized supervising TASK, written as the binary it runs —
+#               the path init was started as for its own services, the device
+#               manager's path for the drivers it starts. The one word that is not
+#               a path is 'kernel', because a kernel task has no binary; that is
+#               what the test harness's direct spawns look like.
+#               Matched by IDENTITY, not by spelling. Name alone is not identity —
+#               spawn is ungated, so a hostile process can start a granted binary
+#               itself and inherit its grants; and it can equally start its own
+#               instance of the *supervisor's* binary and have that spawn the
+#               granted one, at which point both names read correctly (the
+#               laundering deputy). So init also asks which task the supervisor
+#               is: 'kernel' means supervisor id 0, which only the kernel can
+#               confer; init's own path means this init; any other path means a
+#               task init spawned itself or one the kernel spawned. Task ids are
+#               monotonic and never reused, so an id cannot be borrowed.
+#   permission  bind (provide this contract) | open (speak to it) |
+#               supervise (stand in someone else's chain — see below)
+#   name        the contract, relative to /protocol
+#
+# A trailing '*' on any field matches any tail — how a subtree is granted whole.
+#
+# 'supervise' exists because attestation is one hop deep and the driver tree is
+# three: the device manager starts the PS/2 bus, and the bus starts the keyboard
+# and mouse drivers. Init never met the bus, so it cannot vouch for it by
+# acquaintance — and it must not vouch for it by name, or the laundering deputy
+# walks straight in. A 'supervise' row is the manifest saying it: a task running
+# this binary, under this supervisor, may be the supervising task an 'open' row
+# names, for this contract and no other. It grants the delegate nothing itself,
+# and it is deliberately open-only — a delegate may vouch for what its children
+# REACH, never for what they CLAIM, so every bind refusal is untouched by it.
+#
+# binary                                     supervisor                       permission  name
+
+# --- the services init spawns from init.csv ---------------------------------
+/system/services/input,                      /system/services/init,           bind,       input
+/system/services/device-manager,             /system/services/init,           bind,       device-manager
+/system/services/fat,                        /system/services/init,           bind,       vfs
+/system/services/display,                    /system/services/init,           bind,       display
+
+# The discovery service ships under one neutral name per firmware (docs/discovery.md);
+# on x86 it is the acpi service, and what it provides is the power contract.
+/system/services/discovery,                  /system/services/device-manager, bind,       power
+
+# --- the drivers, which the device manager spawns ---------------------------
+/system/drivers/ps2-bus,                     /system/services/device-manager, bind,       ps2-bus
+/system/drivers/usb-xhci-bus,                /system/services/device-manager, bind,       usb-transfer
+/system/drivers/usb-storage,                 /system/services/device-manager, bind,       block
+/system/drivers/virtio-gpu,                  /system/services/device-manager, bind,       scanout
+
+# --- the same providers when the kernel test harness starts them directly ---
+# A scenario boot spawns its own providers instead of letting init do it
+# (docs/security-track-plan.md, decision 9), so the same binaries appear with
+# 'kernel' as the supervisor. Nothing else changes: the binary must still match.
+/system/services/input,                      kernel,                          bind,       input
+/system/services/device-manager,             kernel,                          bind,       device-manager
+/system/services/fat,                        kernel,                          bind,       vfs
+/system/services/display,                    kernel,                          bind,       display
+/system/services/discovery,                  kernel,                          bind,       power
+
+# --- test fixtures ----------------------------------------------------------
+# The subtree rule, dogfooded: anything installed under /test may claim anything
+# under /protocol/test, and nothing above it — whether the harness spawned it or
+# another fixture did.
+/test/*,                                     kernel,                          bind,       test/*
+/test/*,                                     /test/*,                         bind,       test/*
+
+
+# ============================================================================
+# open — who may REACH each contract. One row per client per contract; a client
+# with no row here simply finds the name absent, forever.
+# ============================================================================
+
+# --- init's own services ----------------------------------------------------
+# fat reaches the block device behind the volume it mounts; the compositor
+# reaches the scanout its driver announced, its own endpoint (the mouse-listener
+# thread opens /protocol/display like any other client — threads share no
+# handles), and the input stream that moves the cursor.
+/system/services/fat,                        /system/services/init,           open,       block
+/system/services/display,                    /system/services/init,           open,       scanout
+/system/services/display,                    /system/services/init,           open,       display
+/system/services/display,                    /system/services/init,           open,       input
+/system/services/display-demo,               /system/services/init,           open,       display
+
+# --- the same two when the kernel test harness starts them directly ---------
+/system/services/display,                    kernel,                          open,       scanout
+/system/services/display,                    kernel,                          open,       display
+/system/services/display,                    kernel,                          open,       input
+/system/services/display-demo,               kernel,                          open,       display
+
+# --- the drivers, and the discovery service ---------------------------------
+# Every driver says hello to the manager that started it — one row for the whole
+# subtree, because that handshake is what being a driver means. The rest are per
+# driver: the storage and HID class drivers talk to their controller, the HID
+# drivers publish into the input stream, and the GPU driver announces its scanout
+# to the compositor.
+/system/drivers/*,                           /system/services/device-manager, open,       device-manager
+/system/services/discovery,                  /system/services/device-manager, open,       device-manager
+/system/drivers/usb-storage,                 /system/services/device-manager, open,       usb-transfer
+/system/drivers/usb-hid-keyboard,            /system/services/device-manager, open,       usb-transfer
+/system/drivers/usb-hid-keyboard,            /system/services/device-manager, open,       input
+/system/drivers/usb-hid-mouse,               /system/services/device-manager, open,       usb-transfer
+/system/drivers/usb-hid-mouse,               /system/services/device-manager, open,       input
+/system/drivers/virtio-gpu,                  /system/services/device-manager, open,       display
+
+# --- the PS/2 child drivers, one hop further down ---------------------------
+# The keyboard and mouse drivers are started by the BUS driver, not by the
+# device manager — the one three-deep chain in the tree. Init cannot vouch for
+# the bus by acquaintance (it never started it), so the manifest authorizes it
+# explicitly, and only for the two contracts its children need.
+/system/drivers/ps2-bus,                     /system/services/device-manager, supervise,  ps2-bus
+/system/drivers/ps2-bus,                     /system/services/device-manager, supervise,  input
+/system/drivers/ps2-keyboard,                /system/drivers/ps2-bus,         open,       ps2-bus
+/system/drivers/ps2-keyboard,                /system/drivers/ps2-bus,         open,       input
+/system/drivers/ps2-mouse,                   /system/drivers/ps2-bus,         open,       ps2-bus
+/system/drivers/ps2-mouse,                   /system/drivers/ps2-bus,         open,       input
+
+# --- test fixtures ----------------------------------------------------------
+# The /protocol/test subtree is theirs whole, the way the bind rows give it to
+# them. Everything ABOVE that subtree is named one fixture at a time, so a
+# fixture reaches a system contract only where a scenario needs it — which is
+# what leaves the rest genuinely absent for the rest of them (the protocol-denied
+# case asks for one it was not given, and is told there is no such thing).
+/test/*,                                     kernel,                          open,       test/*
+/test/*,                                     /test/*,                         open,       test/*
+/test/*,                                     kernel,                          open,       device-manager
+/test/*,                                     /system/services/device-manager, open,       device-manager
+/test/system/services/input-source,          kernel,                          open,       input
+/test/system/services/input-test,            kernel,                          open,       input
+
+# The guessable-id probe (test/system/services/badge-scope-test) runs as two
+# processes of one binary: the owner, which the scenario spawns, and the intruder,
+# which the owner spawns with the ids it holds. Both reach the compositor — the
+# owner to create the layer, the intruder to be refused it — so the binary is
+# named twice, once per supervisor. The second row needs no 'supervise'
+# delegation: the owner was spawned by the KERNEL, which is a chain init can
+# vouch for on its own.
+/test/system/services/badge-scope-test,      kernel,                          open,       display
+/test/system/services/badge-scope-test,      /test/*,                         open,       display
+
+# The conformance probe (test/system/services/protocol-conformance-test) asks
+# every provider its boot bound for the envelope's reserved verbs. It reaches
+# ONLY the two contracts its own scenario boots a provider for, named one at a
+# time exactly like the two rows above — no subtree, no wildcard. Everything else
+# under /protocol stays absent for it, which is the point: the fixture walks the
+# namespace listing and reports what it could not open rather than being handed
+# the tree to make the test look broad.
+/test/system/services/protocol-conformance-test, kernel,                      open,       input
+/test/system/services/protocol-conformance-test, kernel,                      open,       display
+
+# The laundering-deputy probe (test/system/services/protocol-registry-test) runs
+# a grandchild whose supervisor is a fixture nobody authorized — that is the
+# point of it, and its bind must stay refused. It still has to report the verdict
+# it got, so its reporting channel, and nothing else, is delegated.
+/test/*,                                     /test/*,                         supervise,  test/verdict

system/drivers/pci-bus/build.zig

@@ -0,0 +1,18 @@
+//! The pci-bus driver as a binary package (docs/build-packages-plan.md):
+//! this file names the binary and EXACTLY the modules its source imports —
+//! build-support resolves each name from the domains this zon declares.
+
+const std = @import("std");
+const build_support = @import("build-support");
+
+pub fn build(b: *std.Build) void {
+    const exe = build_support.userBinary(b, .{
+        .name = "pci-bus",
+        .root_source_file = b.path("pci-bus.zig"),
+        .imports = &.{
+            "device-manager-protocol", "driver", "ipc", "logging", "memory", "pci-class",
+            "process", "service",
+        },
+    });
+    b.installArtifact(exe);
+}

system/drivers/pci-bus/build.zig.zon

@@ -0,0 +1,16 @@
+.{
+    .name = .pci_bus,
+    .version = "0.0.0",
+    .fingerprint = 0x283fca121f0bb145, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{
+        // build-support supplies the shared recipe; kernel is implicit in
+        // every binary (the root shim + link script live there). The rest
+        // are exactly the homes of this binary's declared imports.
+        .@"build-support" = .{ .path = "../../../build-support" },
+        .kernel = .{ .path = "../../../library/kernel" },
+        .device = .{ .path = "../../../library/device" },
+        .protocol = .{ .path = "../../../library/protocol" },
+    },
+    .paths = .{""},
+}

system/drivers/pci-bus/pci-bus.zig

@@ -21,7 +21,7 @@ const logging = @import("logging");
 const device_manager_protocol = @import("device-manager-protocol");
 const pci_class = @import("pci-class");
 
-/// Log a discovered function as its would-be /etc/devices.csv columns (bus, base,
+/// Log a discovered function as its would-be /system/configuration/devices.csv columns (bus, base,
 /// class, prog_if, vendor, device, subsystem) followed by the human-readable
 /// class/subclass/prog-IF names — so a row for a new driver reads straight off the
 /// boot log. `subsystem` prints as `*` when the function has none, matching the CSV
@@ -154,7 +154,7 @@ fn registerAndReport(bus: u64, dev: u64, function: u64, class_triple: u32) void
     descriptor.class = @intFromEnum(device.DeviceClass.pci_device);
     descriptor.pci_class = class_triple;
     // Vendor/device from the first config dword (0x00): low half vendor, high half
-    // device. These carry to the manager's /etc/devices.csv matcher so a function
+    // device. These carry to the manager's /system/configuration/devices.csv matcher so a function
     // can bind on its exact 1AF4:1050 identity, not just its class triple.
     const vendor_device = configRead(bus, dev, function, 0x00);
     descriptor.vendor = @truncate(vendor_device);
@@ -229,27 +229,30 @@ fn registerAndReport(bus: u64, dev: u64, function: u64, class_triple: u32) void
         std.log.info("register refused for {d}:{d}.{d}", .{ bus, dev, function });
         return;
     };
-    const report = device_manager_protocol.ChildAdded{
+    // The registered device id is the packet's target — the manager's object
+    // addressing — so the report body carries only where on the bus it sits and
+    // what it is.
+    var packet: [device_manager_protocol.message_maximum]u8 = undefined;
+    const framed = device_manager_protocol.Protocol.encodeRequest(.child_added, registered, .{
         .bus = @intFromEnum(device_manager_protocol.BusKind.pci),
         .parent = bridge_id,
         .bus_address = (bus << 8) | (dev << 3) | function,
         .identity = class_triple,
-        .device_id = registered,
         .vendor = descriptor.vendor,
         .device = descriptor.device,
         .subsystem = descriptor.subsystem,
-    };
+    }, &.{}, &packet) orelse return;
     var reply: [device_manager_protocol.message_maximum]u8 = undefined;
-    _ = ipc.call(manager_handle, std.mem.asBytes(&report), &reply) catch {
+    _ = ipc.call(manager_handle, framed, &reply) catch {
         std.log.info("child report for {d}:{d}.{d} failed", .{ bus, dev, function });
     };
 }
 
-fn onMessage(message: []const u8, reply: []u8, sender: u32, capability: ?ipc.Handle) usize {
+fn onMessage(message: []const u8, reply: []u8, sender: u32, arrived: *ipc.Arrival) usize {
     _ = message;
     _ = reply;
     _ = sender;
-    _ = capability;
+    _ = arrived; // nothing here takes a capability: the harness closes what arrives
     return 0;
 }
 

system/drivers/ps2-bus/build.zig

@@ -0,0 +1,50 @@
+//! The ps2-bus driver as a binary package (docs/build-packages-plan.md):
+//! this file names the binary and EXACTLY the modules its source imports —
+//! build-support resolves each name from the domains this zon declares.
+
+const std = @import("std");
+const build_support = @import("build-support");
+
+pub fn build(b: *std.Build) void {
+    const ps2_bus_exe = build_support.userBinary(b, .{
+        .name = "ps2-bus",
+        .root_source_file = b.path("ps2-bus.zig"),
+        .imports = &.{ "acpi-ids", "channel", "driver", "ipc", "logging", "memory", "process", "service", "time" },
+    });
+    b.installArtifact(ps2_bus_exe);
+
+    const ps2_keyboard_exe = build_support.userBinary(b, .{
+        .name = "ps2-keyboard",
+        .root_source_file = b.path("keyboard.zig"),
+        .imports = &.{
+            "acpi-ids",       "channel", "driver", "input-client", "input-protocol", "ipc",
+            "logging",        "memory",  "process", "time",         "xkeyboard-config",
+        },
+    });
+    b.installArtifact(ps2_keyboard_exe);
+
+    const ps2_mouse_exe = build_support.userBinary(b, .{
+        .name = "ps2-mouse",
+        .root_source_file = b.path("mouse.zig"),
+        .imports = &.{
+            "acpi-ids", "channel", "driver", "input-client", "input-protocol", "ipc", "logging",
+            "memory",   "process", "time",
+        },
+    });
+    b.installArtifact(ps2_mouse_exe);
+
+    // Standalone `zig build test`; the root aggregate depends on this step.
+    const test_step = b.step("test", "Run the ps2-bus unit tests");
+    for ([_][]const u8{
+        "scancode.zig", // set-2 decode + keyboard state machine
+        "mouse-packet.zig", // 3-byte mouse packet assembly
+    }) |test_root| {
+        const unit_tests = b.addTest(.{
+            .root_module = b.createModule(.{
+                .root_source_file = b.path(test_root),
+                .target = b.resolveTargetQuery(.{}),
+            }),
+        });
+        test_step.dependOn(&b.addRunArtifact(unit_tests).step);
+    }
+}

system/drivers/ps2-bus/build.zig.zon

@@ -0,0 +1,18 @@
+.{
+    .name = .ps2_bus,
+    .version = "0.0.0",
+    .fingerprint = 0x642a365353bf7de9, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{
+        // build-support supplies the shared recipe; kernel is implicit in
+        // every binary (the root shim + link script live there). The rest
+        // are exactly the homes of this binary's declared imports.
+        .@"build-support" = .{ .path = "../../../build-support" },
+        .kernel = .{ .path = "../../../library/kernel" },
+        .client = .{ .path = "../../../library/client" },
+        .device = .{ .path = "../../../library/device" },
+        .protocol = .{ .path = "../../../library/protocol" },
+        .@"xkeyboard-config" = .{ .path = "../../../library/xkeyboard-config" },
+    },
+    .paths = .{""},
+}

system/drivers/ps2-bus/keyboard.zig

@@ -16,10 +16,11 @@
 
 const std = @import("std");
 const device = @import("driver");
+const channel = @import("channel");
 const ipc = @import("ipc");
 const process = @import("process");
 const time = @import("time");
-const input = @import("input");
+const input = @import("input-client");
 const memory = @import("memory");
 const logging = @import("logging");
 const xkb = @import("xkeyboard-config");
@@ -27,12 +28,12 @@ const ps2 = @import("ps2-library.zig");
 const scancode = @import("scancode.zig");
 const input_protocol = @import("input-protocol");
 
-/// Look up the ps2-bus service, retrying while the bus (which spawned us before
+/// Open `/protocol/ps2-bus`, retrying while the bus (which spawned us before
-/// registering) is still coming up.
+/// binding) is still coming up.
 fn lookupBus() ?ipc.Handle {
     var attempts: usize = 0;
     while (attempts < 100) : (attempts += 1) {
-        if (ipc.lookup(.ps2_bus)) |handle| return handle;
+        if (channel.openEndpoint("ps2-bus")) |handle| return handle;
         time.sleepMillis(50);
     }
     return null;

system/drivers/ps2-bus/mouse.zig

@@ -16,22 +16,23 @@
 
 const std = @import("std");
 const device = @import("driver");
+const channel = @import("channel");
 const ipc = @import("ipc");
 const process = @import("process");
 const time = @import("time");
-const input = @import("input");
+const input = @import("input-client");
 const memory = @import("memory");
 const logging = @import("logging");
 const ps2 = @import("ps2-library.zig");
 const mouse_packet = @import("mouse-packet.zig");
 const input_protocol = @import("input-protocol");
 
-/// Look up the ps2-bus service, retrying while the bus (which spawned us before
+/// Open `/protocol/ps2-bus`, retrying while the bus (which spawned us before
-/// registering) is still coming up.
+/// binding) is still coming up.
 fn lookupBus() ?ipc.Handle {
     var attempts: usize = 0;
     while (attempts < 100) : (attempts += 1) {
-        if (ipc.lookup(.ps2_bus)) |handle| return handle;
+        if (channel.openEndpoint("ps2-bus")) |handle| return handle;
         time.sleepMillis(50);
     }
     return null;

system/drivers/ps2-bus/ps2-bus.zig

@@ -11,6 +11,7 @@
 //!        - irq 0xc len 0x1
 const std = @import("std");
 const device = @import("driver");
+const channel = @import("channel");
 const ipc = @import("ipc");
 const process = @import("process");
 const service = @import("service");
@@ -62,7 +63,13 @@ var port_device_types = [_]?ps2.DeviceType{ null, null };
 /// Handle a child driver's `AttachRequest`: record the endpoint capability it
 /// passed as the forwarding target for the port whose device matches its type.
 /// Writes an `AttachReply` into `out` and returns its length.
-fn handleAttach(message: []const u8, got: ipc.Received, out: []u8) usize {
+/// A child driver's AttachRequest. The endpoint it hands over arrives under the
+/// same ownership rule the service harness states (`ipc.Arrival`): the turn owns
+/// it, and only the path that records it in `port_endpoints` says `take`. Every
+/// refusal here simply returns, and the loop closes what arrived — otherwise a
+/// stranger (this is a named contract, reachable by anyone) spends one of this
+/// driver's thirty-two handle slots per malformed attach.
+fn handleAttach(message: []const u8, out: []u8, arrived: *ipc.Arrival) usize {
     const reply = struct {
         fn write(buffer: []u8, status: ps2.AttachStatus) usize {
             const header = ps2.AttachReply{ .status = @intFromEnum(status) };
@@ -73,12 +80,17 @@ fn handleAttach(message: []const u8, got: ipc.Received, out: []u8) usize {
 
     if (message.len < @sizeOf(ps2.AttachRequest)) return reply.write(out, .invalid_request);
     const request = std.mem.bytesToValue(ps2.AttachRequest, message[0..@sizeOf(ps2.AttachRequest)]);
-    const endpoint = got.cap orelse return reply.write(out, .missing_endpoint);
+    const endpoint = arrived.peek() orelse return reply.write(out, .missing_endpoint);
 
     for (&port_device_types, 0..) |maybe_type, port_index| {
         const device_type = maybe_type orelse continue;
         if (@intFromEnum(device_type) != request.device_type) continue;
-        port_endpoints[port_index] = endpoint;
+        // Claimed. A re-attach supersedes the previous driver's endpoint, and the
+        // one it displaces is closed: the slot holds exactly one reference.
+        if (port_endpoints[port_index]) |previous| {
+            if (previous != endpoint) _ = ipc.close(previous);
+        }
+        port_endpoints[port_index] = arrived.take();
         std.log.info("{s} driver attached", .{@tagName(device_type)});
         return reply.write(out, .ok);
     }
@@ -213,15 +225,16 @@ pub fn main() void {
         return;
     };
 
-    // The endpoint the child drivers attach to and IRQ1 wakes. Registered under a
+    // The endpoint the child drivers attach to and IRQ1 wakes. Bound as the
-    // well-known id so the children can find it, the way input subscribers find
+    // `ps2-bus` contract so the children can find it by name, the way input
-    // the input service.
+    // subscribers find the input service. This driver runs its own loop rather
+    // than the service harness, so it binds by hand — same call the harness makes.
     const endpoint = ipc.createIpcEndpoint() orelse {
         _ = logging.write("/system/drivers/ps2-bus: no endpoint\n");
         return;
     };
-    if (!ipc.register(.ps2_bus, endpoint)) {
+    if (!channel.bindPatiently("ps2-bus", endpoint)) {
-        _ = logging.write("/system/drivers/ps2-bus: register failed\n");
+        _ = logging.write("/system/drivers/ps2-bus: could not bind /protocol/ps2-bus\n");
         return;
     }
 
@@ -273,6 +286,13 @@ pub fn main() void {
     var receive: [@sizeOf(ps2.AttachRequest)]u8 = undefined;
     while (true) {
         const got = ipc.replyWait(endpoint, reply_buffer[0..reply_len], &receive, null);
+        // The turn owns whatever capability arrived and closes it unless
+        // `handleAttach` claims it (`ipc.Arrival`) — the kernel installs one
+        // whatever the message's length or kind, so this covers the notification
+        // path and every refusal below it.
+        var arrived: ipc.Arrival = .{ .handle = got.cap };
+        defer arrived.release();
+
         if (got.isNotification()) {
             reply_len = 0;
             if (got.isMessage() or got.isChildExit()) continue; // nothing sends us these
@@ -301,6 +321,6 @@ pub fn main() void {
             }
             continue;
         }
-        reply_len = handleAttach(receive[0..got.len], got, &reply_buffer);
+        reply_len = handleAttach(receive[0..got.len], &reply_buffer, &arrived);
     }
 }

system/drivers/usb-hid/build.zig

@@ -0,0 +1,42 @@
+//! The usb-hid driver as a binary package (docs/build-packages-plan.md):
+//! this file names the binary and EXACTLY the modules its source imports —
+//! build-support resolves each name from the domains this zon declares.
+
+const std = @import("std");
+const build_support = @import("build-support");
+
+pub fn build(b: *std.Build) void {
+    const usb_hid_keyboard_exe = build_support.userBinary(b, .{
+        .name = "usb-hid-keyboard",
+        .root_source_file = b.path("keyboard.zig"),
+        .imports = &.{
+            "driver", "input-client", "input-protocol", "ipc", "logging", "process", "service",
+            "usb", "usb-abi", "xkeyboard-config",
+        },
+    });
+    b.installArtifact(usb_hid_keyboard_exe);
+
+    const usb_hid_mouse_exe = build_support.userBinary(b, .{
+        .name = "usb-hid-mouse",
+        .root_source_file = b.path("mouse.zig"),
+        .imports = &.{
+            "driver", "input-client", "input-protocol", "ipc", "logging", "process", "service",
+            "usb", "usb-abi",
+        },
+    });
+    b.installArtifact(usb_hid_mouse_exe);
+
+    // Standalone `zig build test`; the root aggregate depends on this step.
+    const test_step = b.step("test", "Run the usb-hid unit tests");
+    for ([_][]const u8{
+        "hid-report.zig", // HID boot-report keyboard/mouse decode
+    }) |test_root| {
+        const unit_tests = b.addTest(.{
+            .root_module = b.createModule(.{
+                .root_source_file = b.path(test_root),
+                .target = b.resolveTargetQuery(.{}),
+            }),
+        });
+        test_step.dependOn(&b.addRunArtifact(unit_tests).step);
+    }
+}

system/drivers/usb-hid/build.zig.zon

@@ -0,0 +1,18 @@
+.{
+    .name = .usb_hid,
+    .version = "0.0.0",
+    .fingerprint = 0x66328b738fffff01, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{
+        // build-support supplies the shared recipe; kernel is implicit in
+        // every binary (the root shim + link script live there). The rest
+        // are exactly the homes of this binary's declared imports.
+        .@"build-support" = .{ .path = "../../../build-support" },
+        .kernel = .{ .path = "../../../library/kernel" },
+        .client = .{ .path = "../../../library/client" },
+        .device = .{ .path = "../../../library/device" },
+        .protocol = .{ .path = "../../../library/protocol" },
+        .@"xkeyboard-config" = .{ .path = "../../../library/xkeyboard-config" },
+    },
+    .paths = .{""},
+}

system/drivers/usb-hid/keyboard.zig

@@ -18,7 +18,7 @@ const std = @import("std");
 const ipc = @import("ipc");
 const process = @import("process");
 const service = @import("service");
-const input = @import("input");
+const input = @import("input-client");
 const device_manager = @import("driver");
 const logging = @import("logging");
 const usb = @import("usb");
@@ -112,9 +112,10 @@ pub fn main(init: process.Init) void {
             if (signals.has(.terminate)) return;
             continue;
         }
-        if (!got.isMessage() or got.len < @sizeOf(usb.InterruptReport)) continue;
+        if (!got.isMessage()) continue;
-
+        // An `interrupt_report` event packet: the verb in its folded header, the
-        const message = std.mem.bytesToValue(usb.InterruptReport, receive[0..@sizeOf(usb.InterruptReport)]);
+        // report after it. Anything else on this endpoint is not ours.
+        const message = usb.reportOf(receive[0..got.len]) orelse continue;
         if (message.length < @sizeOf(hid.KeyboardReport)) continue;
         const report = std.mem.bytesToValue(hid.KeyboardReport, message.data[0..@sizeOf(hid.KeyboardReport)]);
         const transitions = decoder.feed(report);

system/drivers/usb-hid/mouse.zig

@@ -14,7 +14,7 @@ const std = @import("std");
 const ipc = @import("ipc");
 const process = @import("process");
 const service = @import("service");
-const input = @import("input");
+const input = @import("input-client");
 const device_manager = @import("driver");
 const logging = @import("logging");
 const usb = @import("usb");
@@ -74,9 +74,10 @@ pub fn main(init: process.Init) void {
             if (signals.has(.terminate)) return;
             continue;
         }
-        if (!got.isMessage() or got.len < @sizeOf(usb.InterruptReport)) continue;
+        if (!got.isMessage()) continue;
-
+        // An `interrupt_report` event packet: the verb in its folded header, the
-        const message = std.mem.bytesToValue(usb.InterruptReport, receive[0..@sizeOf(usb.InterruptReport)]);
+        // report after it. Anything else on this endpoint is not ours.
+        const message = usb.reportOf(receive[0..got.len]) orelse continue;
         const length = @min(message.length, message.data.len);
         const report = hid.parseMouse(message.data[0..length]) orelse continue;
         const mask = buttonMask(report.buttons);

system/drivers/usb-storage/build.zig

@@ -0,0 +1,33 @@
+//! The usb-storage driver as a binary package (docs/build-packages-plan.md):
+//! this file names the binary and EXACTLY the modules its source imports —
+//! build-support resolves each name from the domains this zon declares.
+
+const std = @import("std");
+const build_support = @import("build-support");
+
+pub fn build(b: *std.Build) void {
+    const exe = build_support.userBinary(b, .{
+        .name = "usb-storage",
+        .root_source_file = b.path("usb-storage.zig"),
+        .imports = &.{
+            "block-protocol", "driver", "envelope", "ipc", "logging", "memory", "process",
+            "service",        "time",   "usb",
+        },
+    });
+    b.installArtifact(exe);
+
+    // Standalone `zig build test`; the root aggregate depends on this step.
+    const test_step = b.step("test", "Run the usb-storage unit tests");
+    for ([_][]const u8{
+        "bulk-only-transport.zig", // CBW/CSW wrapper sizes
+        "scsi.zig", // SCSI CDB encodings (big-endian)
+    }) |test_root| {
+        const unit_tests = b.addTest(.{
+            .root_module = b.createModule(.{
+                .root_source_file = b.path(test_root),
+                .target = b.resolveTargetQuery(.{}),
+            }),
+        });
+        test_step.dependOn(&b.addRunArtifact(unit_tests).step);
+    }
+}

system/drivers/usb-storage/build.zig.zon

@@ -0,0 +1,16 @@
+.{
+    .name = .usb_storage,
+    .version = "0.0.0",
+    .fingerprint = 0xce09fdc4c50bb4fe, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{
+        // build-support supplies the shared recipe; kernel is implicit in
+        // every binary (the root shim + link script live there). The rest
+        // are exactly the homes of this binary's declared imports.
+        .@"build-support" = .{ .path = "../../../build-support" },
+        .kernel = .{ .path = "../../../library/kernel" },
+        .device = .{ .path = "../../../library/device" },
+        .protocol = .{ .path = "../../../library/protocol" },
+    },
+    .paths = .{""},
+}

system/drivers/usb-storage/usb-storage.zig

@@ -22,8 +22,16 @@ const logging = @import("logging");
 const usb = @import("usb");
 const scsi = @import("scsi.zig");
 const bot = @import("bulk-only-transport.zig");
+const envelope = @import("envelope");
 const block_protocol = @import("block-protocol");
 
+/// The generated block dispatch. One device per process, so the handler context
+/// is empty and the geometry stays in this file's globals.
+const Serve = block_protocol.Protocol.Provider(void);
+
+const Invocation = envelope.Invocation;
+const Answer = envelope.Answer;
+
 var device_id: u64 = 0;
 var device: usb.Device = undefined;
 var bulk_in: usb.Endpoint = undefined;
@@ -90,9 +98,22 @@ fn initialise(endpoint: ipc.Handle) bool {
         bring_up_failed = true;
         return false;
     };
-    command_wrapper = memory.dmaAlloc(4096, memory.dma_coherent) orelse return false;
+    // Shareable, so each buffer's capability can be handed to the controller: usb-storage
-    status_wrapper = memory.dmaAlloc(4096, memory.dma_coherent) orelse return false;
+    // owns no device, so its buffers are not auto-bound anywhere — the controller reaches
-    command_data = memory.dmaAlloc(4096, memory.dma_coherent) orelse return false;
+    // them only once attached. (No-op binding when no IOMMU is enforcing.)
+    command_wrapper = memory.dmaAlloc(4096, memory.dma_coherent | memory.dma_shareable) orelse return false;
+    status_wrapper = memory.dmaAlloc(4096, memory.dma_coherent | memory.dma_shareable) orelse return false;
+    command_data = memory.dmaAlloc(4096, memory.dma_coherent | memory.dma_shareable) orelse return false;
+    for ([_]memory.DmaRegion{ command_wrapper, status_wrapper, command_data }) |region| {
+        if (region.handle) |handle| {
+            if (!device.attachDma(handle)) {
+                _ = logging.write("/system/drivers/usb-storage: could not attach a DMA buffer to the controller\n");
+                bring_up_failed = true;
+                return false;
+            }
+            _ = ipc.close(handle); // the binding holds its own reference now
+        }
+    }
 
     // Bring the LUN up: wait for it to be ready (clearing the initial unit-attention
     // with REQUEST SENSE), identify it, and read its capacity.
@@ -131,45 +152,65 @@ fn initialise(endpoint: ipc.Handle) bool {
     return true;
 }
 
-/// Serve the block protocol: geometry, and whole-block read/write to/from the
+// --- serving the block protocol ---------------------------------------------
-/// caller's DMA buffer (named by physical address).
+//
-fn onMessage(message: []const u8, reply: []u8, sender: u32, capability: ?ipc.Handle) usize {
+// Geometry, and whole-block read/write to and from the caller's DMA buffer
-    _ = sender;
+// (named by physical address). One device per process, so `Header.target` is
-    _ = capability;
+// always 0 and no handler reads it.
-    if (message.len < block_protocol.request_size) return 0;
+
-    const request = std.mem.bytesToValue(block_protocol.Request, message[0..block_protocol.request_size]);
+/// A transfer the device refused. Every failure here is the same one — the SCSI
-    switch (request.operation) {
+/// command did not complete — so there is one errno for all of them.
-        @intFromEnum(block_protocol.Operation.geometry) => {
+const refused: isize = -envelope.ENOENT;
-            return writeReply(reply, .{ .status = 0, .block_size = block_size, .block_count = block_count });
+
-        },
+fn onGeometry(_: void, _: Invocation(void), answer: Answer(block_protocol.Geometry)) isize {
-        @intFromEnum(block_protocol.Operation.read) => {
+    answer.set(.{ .block_size = block_size, .block_count = block_count });
-            const count: u16 = @intCast(request.count);
+    return 0;
-            const cdb = scsi.read10(@intCast(request.lba), count);
-            const ok = transact(&cdb, true, request.physical, request.count * block_size);
-            return writeReply(reply, .{ .status = if (ok) 0 else -1, .block_size = block_size, .block_count = if (ok) request.count else 0 });
-        },
-        @intFromEnum(block_protocol.Operation.write) => {
-            const count: u16 = @intCast(request.count);
-            const cdb = scsi.write10(@intCast(request.lba), count);
-            const ok = transact(&cdb, false, request.physical, request.count * block_size);
-            return writeReply(reply, .{ .status = if (ok) 0 else -1, .block_size = block_size, .block_count = if (ok) request.count else 0 });
-        },
-        @intFromEnum(block_protocol.Operation.flush) => {
-            // SYNCHRONIZE CACHE: commit the device's write cache to flash. No data
-            // stage. Makes prior writes durable before a caller (init at shutdown)
-            // cuts power. A device without a volatile cache reports success anyway.
-            const cdb = scsi.synchronizeCache10();
-            const ok = transact(&cdb, false, 0, 0);
-            return writeReply(reply, .{ .status = if (ok) 0 else -1, .block_size = block_size, .block_count = 0 });
-        },
-        else => return 0,
-    }
 }
 
-fn writeReply(reply: []u8, value: block_protocol.Reply) usize {
+fn onRead(_: void, invocation: Invocation(block_protocol.Transfer), answer: Answer(block_protocol.Transferred)) isize {
-    const bytes = std.mem.asBytes(&value);
+    const request = invocation.request;
-    @memcpy(reply[0..bytes.len], bytes);
+    const cdb = scsi.read10(@intCast(request.lba), @intCast(request.count));
-    return bytes.len;
+    if (!transact(&cdb, true, request.physical, request.count * block_size)) return refused;
+    answer.set(.{ .count = request.count });
+    return 0;
+}
+
+fn onWrite(_: void, invocation: Invocation(block_protocol.Transfer), answer: Answer(block_protocol.Transferred)) isize {
+    const request = invocation.request;
+    const cdb = scsi.write10(@intCast(request.lba), @intCast(request.count));
+    if (!transact(&cdb, false, request.physical, request.count * block_size)) return refused;
+    answer.set(.{ .count = request.count });
+    return 0;
+}
+
+/// SYNCHRONIZE CACHE: commit the device's write cache to flash. No data stage.
+/// Makes prior writes durable before a caller (init at shutdown) cuts power. A
+/// device without a volatile cache reports success anyway.
+fn onFlush(_: void, _: Invocation(void), _: Answer(void)) isize {
+    const cdb = scsi.synchronizeCache10();
+    return if (transact(&cdb, false, 0, 0)) 0 else refused;
+}
+
+/// The filesystem's DMA buffer: forward its capability to the controller so the
+/// device can reach it. Never claimed — the binding holds its own reference, so
+/// our copy is the turn's to close, on this path and on the refusal alike.
+fn onAttach(_: void, invocation: Invocation(void), _: Answer(void)) isize {
+    const handle = invocation.capability orelse return -envelope.EPROTO;
+    return if (device.attachDma(handle)) 0 else refused;
+}
+
+const handlers = Serve.Handlers{
+    .geometry = onGeometry,
+    .read = onRead,
+    .write = onWrite,
+    .flush = onFlush,
+    .attach = onAttach,
+};
+
+fn onMessage(message: []const u8, reply: []u8, sender: u32, arrived: *ipc.Arrival) usize {
+    // Peeked, never taken: `attach` forwards the capability and the controller's
+    // binding takes its own reference, so this copy stays the turn's to close.
+    return Serve.dispatch({}, handlers, message, sender, arrived.peek(), reply);
 }
 
 pub fn main(init: process.Init) void {
@@ -182,7 +223,7 @@ pub fn main(init: process.Init) void {
         return;
     };
     service.run(block_protocol.message_maximum, .{
-        .service = .block,
+        .service = "block",
         .init = initialise,
         .on_message = onMessage,
     });

system/drivers/usb-xhci-bus/build.zig

@@ -0,0 +1,20 @@
+//! The usb-xhci-bus driver as a binary package (docs/build-packages-plan.md):
+//! this file names the binary and EXACTLY the modules its source imports —
+//! build-support resolves each name from the domains this zon declares.
+
+const std = @import("std");
+const build_support = @import("build-support");
+
+pub fn build(b: *std.Build) void {
+    const exe = build_support.userBinary(b, .{
+        .name = "usb-xhci-bus",
+        .root_source_file = b.path("usb-xhci-bus.zig"),
+        .imports = &.{
+            "channel", "device-manager-protocol", "driver",  "envelope",
+            "input-client", "ipc",                  "logging", "memory",
+            "mmio",    "pci",                       "process", "service",
+            "time",    "usb-abi",                   "usb-ids", "usb-transfer-protocol",
+        },
+    });
+    b.installArtifact(exe);
+}