add app test suite — unit, widget, golden, a11y (168 tests)

Four layers under app/test/:

  * kernel/, extension/ — unit tests for every kernel service and
    the extension contract. i18n fallback chain gets the full
    matrix (exact/lang/default/placeholder, namespace isolation,
    unknown namespace, interpolation). Theme resolver and
    extension-manager topo sort covered.
  * widgets/, builtin/ — widget tests for every primitive and each
    Tier 0 built-in. Assertions reach into the Semantics node so
    a missing label fails structurally, not visually.
  * goldens/ — Alchemist + Ahem font for cross-platform pixel
    stability; primitives only (button, tab bar, icon set). No
    goldens for compositions — they'd churn through every tier.
  * a11y/ — contract-level gate: semantic coverage walks the
    built-in catalogue, contrast walks every token pair in every
    bundled theme against WCAG-AA thresholds (catches real
    regressions: the first run caught `tab.inactive_text` at 2.81
    in summer-night), i18n coverage asserts every referenced key
    exists in its catalog (exists-in-map, not "key == value" — too
    ambiguous for keys that happen to equal their translation).

Helpers under helpers/: `KernelFixture.create()` boots a
KernelServices with in-memory stores + a FakeDaemonClient (no
socket, drivable connected-state), `widget_harness` wraps a
widget in the minimum tree that resolves theme + i18n.

Co-Authored-By: Claude <noreply@anthropic.com>

app/test/builtin/default_layout/widget_test.dart

@@ -0,0 +1,52 @@
+import 'package:clide_app/builtin/default_layout/default_layout.dart';
+import 'package:clide_app/extension/extension.dart';
+import 'package:clide_app/kernel/kernel.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../../helpers/kernel_fixture.dart';
+
+void main() {
+  group('DefaultLayoutExtension', () {
+    late KernelFixture f;
+
+    setUp(() async => f = await KernelFixture.create());
+    tearDown(() async => f.dispose());
+
+    test('activates and applies the classic preset', () async {
+      f.services.extensions.register(DefaultLayoutExtension());
+      await f.services.extensions.activateAll();
+      expect(
+          f.services.arrangement.positionOf(Slots.sidebar), SlotPosition.left);
+      expect(f.services.arrangement.sizeOf(Slots.sidebar), 240);
+      expect(f.services.arrangement.positionOf(Slots.workspace),
+          SlotPosition.center);
+      expect(f.services.arrangement.positionOf(Slots.statusbar),
+          SlotPosition.bottom);
+    });
+
+    test('contributes a layout.reset command', () async {
+      f.services.extensions.register(DefaultLayoutExtension());
+      await f.services.extensions.activateAll();
+      final reset = f.services.commands.get('layout.reset');
+      expect(reset, isNotNull);
+    });
+
+    test('layout.reset re-applies the preset', () async {
+      f.services.extensions.register(DefaultLayoutExtension());
+      await f.services.extensions.activateAll();
+      f.services.arrangement.setSize(Slots.sidebar, 300);
+      expect(f.services.arrangement.sizeOf(Slots.sidebar), 300);
+      final resp = await f.services.commands.execute('layout.reset');
+      expect(resp.ok, true);
+      expect(f.services.arrangement.sizeOf(Slots.sidebar), 240);
+    });
+
+    test('declares a layout preset contribution', () {
+      final ext = DefaultLayoutExtension();
+      expect(
+        ext.contributions.whereType<LayoutPresetContribution>(),
+        hasLength(1),
+      );
+    });
+  });
+}