feat(settings): per-field scope tags + scope resolution (T-449)

Each settings field gains a scope tag showing where its value lives — folder
= Project (.clide), globe = Always (~/.clide), circle-dashed = Default/unset —
colour-coded (statusSuccess / statusWarning / muted) with a tooltip. Tapping
opens a menu to move the value between the scopes the key supports, or reset
to default; the tag's menu replaces the interim reset button.

Backs it with scope-explicit SettingsStore access — rawAt / setAt / removeAt /
effectiveLayer / writableLayers — over the two storage files (app ~/.clide,
project .clide). ext.* keys layer project-over-app; app.*/project.* keys live
only in their prefix's file, so their menu offers that one scope + reset.

Tests: store scope ops (layering, reload, guards) and the tag (Default vs
All-clide rendering, menu reset).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/builtin/settings_ui/category_view_test.dart

@@ -102,14 +102,28 @@ void main() {
       expect(f.services.settings.get<String>('app.demo.level'), 'debug');
     });
 
-    testWidgets('reset control appears for a non-default value and restores the default', (tester) async {
+  });
+
+  group('scope tag (T-449)', () {
+    testWidgets('an unset field shows the Default scope tag', (tester) async {
+      await tester.pumpWidget(harness(f, _bounded(const SettingsCategoryView(category: _category))));
+      expect(find.bySemanticsLabel('Size scope: Default'), findsOneWidget);
+    });
+
+    testWidgets('a value stored at app scope shows the All clide tag', (tester) async {
       await tester.runAsync(() => f.services.settings.set('app.demo.flag', true));
       await tester.pumpWidget(harness(f, _bounded(const SettingsCategoryView(category: _category))));
-      final reset = find.bySemanticsLabel('Reset to default');
-      expect(reset, findsOneWidget);
-      await tester.tap(reset);
+      expect(find.bySemanticsLabel('Flag scope: All clide'), findsOneWidget);
+    });
+
+    testWidgets('the scope menu resets the value to default', (tester) async {
+      await tester.runAsync(() => f.services.settings.set('app.demo.flag', true));
+      await tester.pumpWidget(harness(f, _bounded(const SettingsCategoryView(category: _category))));
+      await tester.tap(find.bySemanticsLabel('Flag scope: All clide'));
       await tester.pump();
-      expect(f.services.settings.get<bool>('app.demo.flag'), isFalse);
+      await tester.tap(find.text('Reset to default'));
+      await tester.pump();
+      expect(f.services.settings.effectiveLayer('app.demo.flag'), isNull);
     });
   });
 

test/kernel/src/settings_scope_test.dart

@@ -0,0 +1,71 @@
+import 'dart:io';
+
+import 'package:clide/kernel/kernel.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  late Directory appDir;
+  late Directory projDir;
+  late SettingsStore store;
+
+  setUp(() async {
+    appDir = await Directory.systemTemp.createTemp('clide_app_');
+    projDir = await Directory.systemTemp.createTemp('clide_proj_');
+    store = SettingsStore(appDir: appDir, projectDir: projDir);
+    await store.load();
+  });
+
+  tearDown(() async {
+    store.dispose();
+    await appDir.delete(recursive: true);
+    await projDir.delete(recursive: true);
+  });
+
+  group('SettingsStore scope-explicit access (T-449)', () {
+    test('writableLayers honours the key prefix', () {
+      expect(store.writableLayers('app.x'), [SettingsScope.app]);
+      expect(store.writableLayers('project.x'), [SettingsScope.project]);
+      expect(store.writableLayers('ext.x'), [SettingsScope.project, SettingsScope.app]);
+    });
+
+    test('ext.* value: project overrides app, and effectiveLayer tracks it', () async {
+      await store.setAt(SettingsScope.app, 'ext.k', 'a');
+      expect(store.rawAt(SettingsScope.app, 'ext.k'), 'a');
+      expect(store.effectiveLayer('ext.k'), SettingsScope.app);
+      expect(store.get<String>('ext.k'), 'a');
+
+      await store.setAt(SettingsScope.project, 'ext.k', 'p');
+      expect(store.effectiveLayer('ext.k'), SettingsScope.project);
+      expect(store.get<String>('ext.k'), 'p');
+
+      await store.removeAt(SettingsScope.project, 'ext.k');
+      expect(store.effectiveLayer('ext.k'), SettingsScope.app);
+      expect(store.get<String>('ext.k'), 'a');
+
+      await store.removeAt(SettingsScope.app, 'ext.k');
+      expect(store.effectiveLayer('ext.k'), isNull);
+      expect(store.get<String>('ext.k'), isNull);
+    });
+
+    test('writes survive a reload from disk', () async {
+      await store.setAt(SettingsScope.project, 'ext.k', 'p');
+      await store.setAt(SettingsScope.app, 'app.y', 1);
+      await store.load();
+      expect(store.rawAt(SettingsScope.project, 'ext.k'), 'p');
+      expect(store.get<int>('app.y'), 1);
+    });
+
+    test('setAt(project) with no project open throws', () async {
+      final noProj = SettingsStore(appDir: appDir);
+      await noProj.load();
+      expect(() => noProj.setAt(SettingsScope.project, 'project.x', 1), throwsStateError);
+      noProj.dispose();
+    });
+
+    test('ext is a key class, not a storage layer', () {
+      expect(() => store.setAt(SettingsScope.ext, 'ext.k', 1), throwsArgumentError);
+      expect(() => store.removeAt(SettingsScope.ext, 'ext.k'), throwsArgumentError);
+      expect(store.rawAt(SettingsScope.ext, 'ext.k'), isNull);
+    });
+  });
+}