build: keep test fixtures out of a no-option build

A plain `zig build` was baking all 11 /test/system/services fixtures into the
production image. Split the bundle: the production set always, the userspace test
fixtures only when -Dtest-case is set — which the QEMU harness passes for every
scenario, exactly when the fixtures are needed on the boot volume. So `zig build`
with no options now ships a clean image (no test binaries in the manifest,
capsule, or FAT tree) and assumes neither -Dtest-case nor -Ddiagnose (the
diagnose display-omission was already gated by the init.csv selection).

Verified: a plain build has zero /test entries in the manifest; -Dtest-case=smoke
includes all fixtures; the args/vfs/device-list QEMU scenarios still pass.

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

build.zig

@@ -773,7 +773,7 @@ pub fn build(b: *std.Build) void {
     // variant that omits the display stack (so the kernel's boot transcript stays
     // on screen); both are bundled at the same /etc/init.csv path.
     const init_csv_source = if (diagnose) "etc/init-diagnose.csv" else "etc/init.csv";
-    const bundled = [_]BundledBinary{
+    const production_bundled = [_]BundledBinary{
         .{ .path = "system/services/init", .binary = init_exe.getEmittedBin() },
         .{ .path = "system/services/fat", .binary = fat_exe.getEmittedBin() },
         .{ .path = "system/services/display", .binary = display_exe.getEmittedBin() },
@@ -798,6 +798,13 @@ pub fn build(b: *std.Build) void {
         .{ .path = "system/drivers/usb-storage", .binary = usb_storage_exe.getEmittedBin() },
         .{ .path = "system/drivers/virtio-gpu", .binary = virtio_gpu_exe.getEmittedBin() },
         .{ .path = "system/drivers/pci-bus", .binary = pci_bus_exe.getEmittedBin() },
+    };
+    // The userspace test fixtures under /test. A plain `zig build` produces a clean
+    // image WITHOUT them; they are bundled only for a test build — which the QEMU
+    // harness signals by passing -Dtest-case=<name> for every scenario, exactly when
+    // these fixtures must be on the boot volume. Merely building this array never
+    // forces a compile: the fixture exes build only if `bundled` (below) includes them.
+    const test_bundled = [_]BundledBinary{
         .{ .path = "test/system/services/vfs-test", .binary = vfstest_exe.getEmittedBin() },
         .{ .path = "test/system/services/fat-test", .binary = fat_test_exe.getEmittedBin() },
         .{ .path = "test/system/services/shared-memory-server", .binary = shared_memory_server_exe.getEmittedBin() },
@@ -810,6 +817,13 @@ pub fn build(b: *std.Build) void {
         .{ .path = "test/system/services/process-test", .binary = process_test_exe.getEmittedBin() },
         .{ .path = "test/system/services/thread-test", .binary = thread_test_exe.getEmittedBin() },
     };
+    // A no-option build assumes neither -Dtest-case nor -Ddiagnose: it ships the
+    // production set only. Test fixtures join in only under -Dtest-case; the
+    // diagnose display-omission is already handled by init_csv_source above.
+    var bundled_list: std.ArrayListUnmanaged(BundledBinary) = .empty;
+    bundled_list.appendSlice(b.allocator, &production_bundled) catch @panic("OOM");
+    if (test_case != null) bundled_list.appendSlice(b.allocator, &test_bundled) catch @panic("OOM");
+    const bundled = bundled_list.items;
 
     // 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
@@ -892,7 +906,7 @@ pub fn build(b: *std.Build) void {
     // 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 /mnt/usb.
-    const fat_image = addBootImage(b, exe.getEmittedBin(), efiexe.getEmittedBin(), manifest_file, capsule_img, &bundled);
+    const fat_image = addBootImage(b, exe.getEmittedBin(), efiexe.getEmittedBin(), manifest_file, capsule_img, bundled);
     const fat_image_install = b.addInstallFile(fat_image, "danos-usb.img");
     b.getInstallStep().dependOn(&fat_image_install.step);
 
@@ -901,7 +915,7 @@ pub fn build(b: *std.Build) void {
     // 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 exe_serial = addKernel(b, kernel_target, optimize, kernel_modules, test_case, true);
-    const fat_image_serial = addBootImage(b, exe_serial.getEmittedBin(), efiexe.getEmittedBin(), manifest_file, capsule_img, &bundled);
+    const fat_image_serial = addBootImage(b, exe_serial.getEmittedBin(), efiexe.getEmittedBin(), manifest_file, capsule_img, 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).