reorg: relocate device/service clients (C3/C4)

- device.zig + device-manager.zig -> library/device/driver/driver.zig (module
  "driver"): the driver author's whole interface — device access (claim/mmioMap/
  irqBind/...) plus the device-manager hello() handshake, folded into one import.
- block.zig -> library/device/block/block.zig (a device type).
- display.zig/input.zig -> library/client/{display,input}/ (userspace-service
  clients — they talk to services, not the kernel).

build.zig module graph updated; the runtime shim now maps runtime.device and
runtime.device_manager onto "driver", so consumers stay untouched (migrated in C2).

zig build green; driver-restart, usb-storage, display-native, input pass.

build.zig

@@ -481,32 +481,31 @@ pub fn build(b: *std.Build) void {
         .root_source_file = b.path("library/kernel/start.zig"),
         .imports = &.{ .{ .name = "process", .module = process_module }, .{ .name = "logging", .module = logging_module } },
     });
-    const device_module = b.addModule("device", .{
-        .root_source_file = b.path("library/kernel/device.zig"),
+    // The driver author's interface (library/device/driver): device access + the
+    // device-manager hello handshake, folded together.
+    const driver_module = b.addModule("driver", .{
+        .root_source_file = b.path("library/device/driver/driver.zig"),
         .imports = &.{
             .{ .name = "abi", .module = abi_module },
             .{ .name = "device-abi", .module = device_abi_module },
             .{ .name = "system-call", .module = system_call_module },
-        },
-    });
-    const device_manager_client_module = b.addModule("device-manager", .{
-        .root_source_file = b.path("library/kernel/device-manager.zig"),
-        .imports = &.{
             .{ .name = "ipc", .module = ipc_module },
             .{ .name = "time", .module = time_module },
             .{ .name = "device-manager-protocol", .module = device_manager_protocol_module },
         },
     });
+    // The block-device client — a device type, so library/device/block.
     const block_client_module = b.addModule("block", .{
-        .root_source_file = b.path("library/kernel/block.zig"),
+        .root_source_file = b.path("library/device/block/block.zig"),
         .imports = &.{
             .{ .name = "ipc", .module = ipc_module },
             .{ .name = "time", .module = time_module },
             .{ .name = "block-protocol", .module = block_protocol_module },
         },
     });
+    // Userspace-service clients live in library/client (they talk to services, not the kernel).
     const display_client_module = b.addModule("display", .{
-        .root_source_file = b.path("library/kernel/display.zig"),
+        .root_source_file = b.path("library/client/display/display.zig"),
         .imports = &.{
             .{ .name = "ipc", .module = ipc_module },
             .{ .name = "time", .module = time_module },
@@ -514,7 +513,7 @@ pub fn build(b: *std.Build) void {
         },
     });
     const input_client_module = b.addModule("input", .{
-        .root_source_file = b.path("library/kernel/input.zig"),
+        .root_source_file = b.path("library/client/input/input.zig"),
         .imports = &.{
             .{ .name = "ipc", .module = ipc_module },
             .{ .name = "time", .module = time_module },
@@ -546,8 +545,7 @@ pub fn build(b: *std.Build) void {
             .{ .name = "logging", .module = logging_module },
             .{ .name = "file-system", .module = file_system_module },
             .{ .name = "start", .module = start_module },
-            .{ .name = "device", .module = device_module },
-            .{ .name = "device-manager", .module = device_manager_client_module },
+            .{ .name = "driver", .module = driver_module },
             .{ .name = "input", .module = input_client_module },
             .{ .name = "block", .module = block_client_module },
             .{ .name = "display", .module = display_client_module },

library/device/driver/driver.zig

@@ -1,12 +1,15 @@
-//! User-space device access: enumerate the kernel's device table, claim a device,
-//! map its MMIO, and bind its interrupt. A driver uses these to find and take
-//! ownership of its hardware; the claim is the capability the kernel checks before
-//! mapping registers or routing an IRQ.
+//! library/device/driver — the driver author's interface: enumerate the kernel's device
+//! table, claim a device, map its MMIO, bind its interrupt (the claim is the capability the
+//! kernel checks before mapping registers or routing an IRQ), and say `hello` to the device
+//! manager at startup. The whole kernel + manager surface a driver needs, in one import.
 
 const std = @import("std");
 const abi = @import("abi");
 const device_abi = @import("device-abi");
 const sc = @import("system-call");
+const ipc = @import("ipc");
+const time = @import("time");
+const device_manager_protocol = @import("device-manager-protocol");
 
 pub const DeviceDescriptor = device_abi.DeviceDescriptor;
 pub const ResourceDescriptor = device_abi.ResourceDescriptor;
@@ -129,3 +132,42 @@ pub fn findDeviceDescriptorByHid(buffer: []DeviceDescriptor, hid_needle: []const
 
     return null;
 }
+
+// --- device-manager handshake (folded in from the former device-manager.zig) ---
+
+/// What kind of driver is announcing itself (a bus that reports children, or a leaf
+/// device). Re-exported so callers name it without importing the protocol.
+pub const Role = device_manager_protocol.Role;
+
+const lookup_attempts: u32 = 100;
+const lookup_pause_ms: u64 = 20;
+
+/// Say hello to the device manager and return its endpoint, or null if there is no manager
+/// (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.
+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;
+        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 reply: [device_manager_protocol.reply_size]u8 = undefined;
+    const length = ipc.call(manager, std.mem.asBytes(&message), &reply) catch {
+        std.log.info("hello call failed", .{});
+        return null;
+    };
+    if (length < device_manager_protocol.reply_size or
+        std.mem.bytesToValue(device_manager_protocol.HelloReply, reply[0..device_manager_protocol.reply_size]).status != 0)
+    {
+        std.log.info("hello refused", .{});
+        return null;
+    }
+    std.log.info("hello acknowledged", .{});
+    return manager;
+}

library/kernel/device-manager.zig

@@ -1,59 +0,0 @@
-//! Client side of the device-manager protocol (docs/device-manager.md): the
-//! calls a supervised driver makes *to* the manager, as opposed to
-//! `device-manager-protocol.zig`, which is the wire contract both sides share.
-//!
-//! Today this is just the hello handshake every spawned driver owes. The
-//! manager arms a hello deadline when it spawns a driver
-//! (system/services/device-manager/device-manager.zig): a driver that stays
-//! silent past it is assumed wedged before `main` and stopped, so every driver
-//! calls `hello` early in its startup. The retry-lookup-call-check this used to
-//! be — copied byte-for-byte into each bus and class driver — lives here once.
-
-const std = @import("std");
-const ipc = @import("ipc");
-const time = @import("time");
-const device_manager_protocol = @import("device-manager-protocol");
-
-/// What kind of driver is announcing itself (a bus that reports children, or a
-/// leaf device). Re-exported so callers name it without importing the protocol.
-pub const Role = device_manager_protocol.Role;
-
-/// Endpoint lookups while the manager is still registering, and the pause
-/// between them: 100 x 20 ms = ~2 s, comfortably inside the manager's 3 s hello
-/// deadline (device-manager.zig `hello_deadline_ms`).
-const lookup_attempts: u32 = 100;
-const lookup_pause_ms: u64 = 20;
-
-/// Say hello to the device manager and return its endpoint, or null if there is
-/// no manager (best-effort standalone bring-up) or it refused the handshake
-/// (version mismatch, unknown sender). Bus drivers keep the returned handle to
-/// report children through; a driver that runs fine unsupervised discards it
-/// with `_ =`, and a driver that requires supervision bails on null.
-///
-/// Logs the outcome itself (attribution is the kernel's, via the process's
-/// binary path), so callers stay a single line.
-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;
-        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 reply: [device_manager_protocol.reply_size]u8 = undefined;
-    const length = ipc.call(manager, std.mem.asBytes(&message), &reply) catch {
-        std.log.info("hello call failed", .{});
-        return null;
-    };
-    if (length < device_manager_protocol.reply_size or
-        std.mem.bytesToValue(device_manager_protocol.HelloReply, reply[0..device_manager_protocol.reply_size]).status != 0)
-    {
-        std.log.info("hello refused", .{});
-        return null;
-    }
-    std.log.info("hello acknowledged", .{});
-    return manager;
-}

library/kernel/runtime.zig

@@ -20,9 +20,9 @@ pub const fs = @import("file-system");
 pub const start = @import("start");
 pub const panic = start.panic;
 
-// Device / service clients (relocated to library/device and library/client in C3/C4).
-pub const device = @import("device");
-pub const device_manager = @import("device-manager");
+// Device / service clients (now in library/device/driver, library/device/block, library/client).
+pub const device = @import("driver");
+pub const device_manager = @import("driver"); // hello() folded into driver
 pub const input = @import("input");
 pub const block = @import("block");
 pub const display = @import("display");