init: data-driven boot service list via /etc/init.csv

Replace init's hardcoded boot_services array with an authoritative,
human-readable service list read at boot, mirroring /etc/devices.csv. Each row
is a service binary path followed by its argv; startup order is file order,
shutdown the reverse. There is no hardcoded fallback — a missing file starts
nothing (the no-ramdisk isolation behavior).

- library/csv: shared CSV helpers (comment strip, field iteration) with unit
  tests; device-registry is refactored onto them so both /etc/*.csv files parse
  through one place.
- init reads /etc/init.csv into fixed-max static tables (the same pattern as the
  device registry) and passes each row's argv straight to spawnSupervised. This
  also makes boot-time modes (e.g. device-manager test-usb-restart) expressible
  as data rather than hardcoded.
- Diagnose mode (-Ddiagnose omits the display stack) becomes build-time file
  selection between etc/init.csv and etc/init-diagnose.csv, so init carries no
  comptime service logic; the diagnose build option is dropped from init.
- build.zig: csv module wired; /etc/init.csv bundled into the initrd; the
  device-registry tests move to a dedicated block since they now import csv.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KJqSiLLchDUUCoXn5jsiwd

library/csv/csv.zig

@@ -0,0 +1,56 @@
+//! Minimal CSV helpers shared by the `/etc/*.csv` config files — the device
+//! registry (`/etc/devices.csv`) and the init service list (`/etc/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.
+
+const std = @import("std");
+
+/// Strip a trailing `#` comment and surrounding whitespace from one raw line.
+/// A blank or comment-only line returns "" (length 0) — the caller's skip signal.
+pub fn stripComment(raw: []const u8) []const u8 {
+    const body = if (std.mem.indexOfScalar(u8, raw, '#')) |hash| raw[0..hash] else raw;
+    return std.mem.trim(u8, body, " \t\r\n");
+}
+
+/// Iterate the comma-separated fields of a line body, each trimmed of spaces and
+/// tabs. Build it from a `stripComment`ed body.
+pub const Fields = struct {
+    inner: std.mem.SplitIterator(u8, .scalar),
+
+    /// The next field, trimmed, or null when the row is exhausted.
+    pub fn next(self: *Fields) ?[]const u8 {
+        const field = self.inner.next() orelse return null;
+        return std.mem.trim(u8, field, " \t");
+    }
+};
+
+pub fn fields(body: []const u8) Fields {
+    return .{ .inner = std.mem.splitScalar(u8, body, ',') };
+}
+
+// --- tests -------------------------------------------------------------------
+
+const testing = std.testing;
+
+test "stripComment trims and drops comments" {
+    try testing.expectEqualStrings("a, b", stripComment("  a, b  # trailing\r\n"));
+    try testing.expectEqualStrings("", stripComment("   # whole-line comment"));
+    try testing.expectEqualStrings("", stripComment("   \t "));
+    try testing.expectEqualStrings("x", stripComment("x"));
+}
+
+test "fields splits and trims each column" {
+    var it = fields(stripComment("pci,  03 , 80  ,  /system/drivers/x  # note"));
+    try testing.expectEqualStrings("pci", it.next().?);
+    try testing.expectEqualStrings("03", it.next().?);
+    try testing.expectEqualStrings("80", it.next().?);
+    try testing.expectEqualStrings("/system/drivers/x", it.next().?);
+    try testing.expect(it.next() == null);
+}
+
+test "a single field yields one column then null" {
+    var it = fields(stripComment("/system/services/input"));
+    try testing.expectEqualStrings("/system/services/input", it.next().?);
+    try testing.expect(it.next() == null);
+}