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/extension/src/contribution_test.dart

@@ -0,0 +1,62 @@
+import 'package:clide/clide.dart';
+import 'package:clide_app/extension/extension.dart';
+import 'package:clide_app/kernel/kernel.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('ContributionPoint sealed hierarchy', () {
+    test('TabContribution exposes slot + title + i18n fields', () {
+      final t = TabContribution(
+        id: 'welcome.view',
+        slot: Slots.workspace,
+        title: 'Welcome',
+        titleKey: 'tab.title',
+        i18nNamespace: 'builtin.welcome',
+        priority: -100,
+        build: (_) => const SizedBox.shrink(),
+      );
+      expect(t.id, 'welcome.view');
+      expect(t.slot, Slots.workspace);
+      expect(t.title, 'Welcome');
+      expect(t.titleKey, 'tab.title');
+      expect(t.i18nNamespace, 'builtin.welcome');
+      expect(t.priority, -100);
+    });
+
+    test('StatusItemContribution pins the statusbar slot', () {
+      final s = StatusItemContribution(
+        id: 'ipc-status.indicator',
+        build: (_) => const SizedBox.shrink(),
+      );
+      expect(s.slot, Slots.statusbar);
+    });
+
+    test('CommandContribution has no slot', () {
+      final c = CommandContribution(
+        id: 'theme.pick',
+        command: 'theme.pick',
+        run: (_) async => IpcResponse.ok(id: '', data: const {}),
+      );
+      expect(c.slot, isNull);
+    });
+
+    test('TrayItemContribution pins the tray slot', () {
+      final t = TrayItemContribution(
+        id: 't',
+        label: 'Label',
+        onSelected: () {},
+      );
+      expect(t.slot, Slots.tray);
+    });
+
+    test('ToolbarButtonContribution pins the toolbar slot', () {
+      final b = ToolbarButtonContribution(
+        id: 'save',
+        label: 'Save',
+        onPressed: () {},
+      );
+      expect(b.slot, Slots.toolbar);
+    });
+  });
+}