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/a11y/semantic_coverage_test.dart

@@ -0,0 +1,66 @@
+import 'package:clide_app/builtin/default_layout/default_layout.dart';
+import 'package:clide_app/builtin/ipc_status/ipc_status.dart';
+import 'package:clide_app/builtin/theme_picker/theme_picker.dart';
+import 'package:clide_app/builtin/welcome/welcome.dart';
+import 'package:clide_app/extension/extension.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+/// Cross-extension contract check: every built-in extension declares a
+/// non-empty title + version (so screen readers and the extensions-ui
+/// surface can announce them) and every interactive contribution
+/// carries enough data to build a Semantics node.
+///
+/// Per-widget Semantics-label checks live in each built-in's own
+/// widget_test.dart (`test/builtin/**/widget_test.dart`) — they run
+/// against a real pumped tree and assert the exact `label` + `hint`
+/// reach the user. This file is the "nothing is missing from the
+/// catalog" gate.
+void main() {
+  group('Tier-0 built-in extensions — contract-level coverage', () {
+    final extensions = <ClideExtension>[
+      DefaultLayoutExtension(),
+      WelcomeExtension(),
+      IpcStatusExtension(),
+      ThemePickerExtension(),
+    ];
+
+    for (final ext in extensions) {
+      group(ext.id, () {
+        test('has non-empty title + version', () {
+          expect(ext.title, isNotEmpty);
+          expect(ext.version, isNotEmpty);
+        });
+
+        test('tab contributions carry title + i18n key + namespace', () {
+          final tabs = ext.contributions.whereType<TabContribution>().toList();
+          for (final t in tabs) {
+            expect(t.title, isNotEmpty,
+                reason: '${ext.id} tab ${t.id} missing English title');
+            if (t.titleKey != null) {
+              expect(t.i18nNamespace, isNotNull,
+                  reason:
+                      '${ext.id} tab ${t.id} has titleKey but no namespace');
+            }
+          }
+        });
+
+        test('command contributions carry stable ids', () {
+          final cmds =
+              ext.contributions.whereType<CommandContribution>().toList();
+          for (final c in cmds) {
+            expect(c.command, isNotEmpty);
+            expect(c.id, isNotEmpty);
+          }
+        });
+      });
+    }
+
+    test('every registered tab hits a real slot', () {
+      for (final ext in extensions) {
+        for (final t in ext.contributions.whereType<TabContribution>()) {
+          expect(t.slot.value, isNotEmpty);
+        }
+      }
+    });
+  });
+}