build: phase 2 wave A — services build as packages

init, fat, display, display-demo, device-manager, input, logger, and
the two discovery fillers (acpi, fdt — each exporting an artifact named
"discovery"; the root -Ddiscovery picks which ships) convert to binary
packages on the pci-bus template. init's serial heartbeat flag rides
the dependency options (the root forwards its -Dserial). fat's and
display's unit tests move into their packages and the root aggregate
delegates to them. Boot-image file list unchanged.

system/services/init/build.zig

@@ -0,0 +1,31 @@
+//! init (PID 1) as a binary package (docs/build-packages-plan.md, phase 2):
+//! this file names only what is specific to init — the shared recipe and the
+//! default-import wiring live in build-support. The root build consumes the
+//! artifact for the boot image and forwards its -Dserial here.
+
+const std = @import("std");
+const build_support = @import("build-support");
+
+pub fn build(b: *std.Build) void {
+    const exe = build_support.userBinary(b, .{
+        .name = "init",
+        .root_source_file = b.path("init.zig"),
+        .domains = build_support.domains(b),
+    });
+    // init speaks the power protocol (orderly shutdown, docs/power.md) and
+    // parses its boot service list from /etc/init.csv with the shared csv
+    // helpers. Which services it starts is data, not a compile-time option:
+    // the root build selects which init.csv variant is bundled (-Ddiagnose).
+    build_support.programModule(exe).addImport("power-protocol", b.dependency("protocol", .{}).module("power-protocol"));
+    build_support.programModule(exe).addImport("csv", b.dependency("csv", .{}).module("csv"));
+    // init reads the same `serial` flag the kernel does: its liveness heartbeat
+    // is a serial/test-build diagnostic (the QEMU harness's init tests assert
+    // on it, and -Dserial images emit it), so a flashable image runs a purely
+    // event-driven PID 1 that wakes only for real work. The root build forwards
+    // its top-level -Dserial as this dependency option.
+    const serial = b.option(bool, "serial", "Compile the serial liveness heartbeat in (forwarded from the root -Dserial)") orelse false;
+    const init_options = b.addOptions();
+    init_options.addOption(bool, "serial", serial);
+    build_support.programModule(exe).addImport("build_options", init_options.createModule());
+    b.installArtifact(exe);
+}

system/services/init/build.zig.zon

@@ -0,0 +1,16 @@
+.{
+    .name = .init,
+    .version = "0.0.0",
+    .fingerprint = 0xc674e474eeeced43, // Changing this has security and trust implications.
+    .minimum_zig_version = "0.16.0",
+    .dependencies = .{
+        .@"build-support" = .{ .path = "../../../build-support" },
+        .kernel = .{ .path = "../../../library/kernel" },
+        .device = .{ .path = "../../../library/device" },
+        .client = .{ .path = "../../../library/client" },
+        .@"xkeyboard-config" = .{ .path = "../../../library/xkeyboard-config" },
+        .protocol = .{ .path = "../../../library/protocol" },
+        .csv = .{ .path = "../../../library/csv" },
+    },
+    .paths = .{""},
+}