test sweep: mop up kernel/src/theme residuals (T-91)

10 small tests in test/kernel/src/theme/mop_up_test.dart covering the
scattered last-mile gaps across the theme subsystem:

- ClideTheme.of and ClideTheme.controllerOf inherited-widget lookups
  (both happy path + the FlutterError-throw branch when no ancestor).
- contrast._composite alpha-mix branch via a partially-transparent
  foreground in contrastRatio.
- ContrastFailure.toString format with embedded pair name / ratio /
  minimum.
- ThemeLoader.fromYamlString FormatException on a non-map root.
- ThemeLoader.fromFile happy path with a tempdir YAML.
- Palette.names and SemanticRoles.roles iterables.

Coverage: theme/controller.dart 37/42 -> 42/42; theme/contrast.dart
54/64 -> 62/64 (remaining 2 lines are the failingPairs add-to-list
path, needs a constructed-broken SurfaceTokens to fire);
theme/loader.dart 48/54 -> 53/54 (1 const-ctor phantom);
theme/palette.dart 9/10 -> 10/10; theme/semantic.dart 2/3 -> 3/3.

Total coverage 74.55% -> 74.79%.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/kernel/src/theme/mop_up_test.dart

@@ -0,0 +1,204 @@
+/// Mop-up tests for the small residuals across `lib/kernel/src/theme/`:
+/// ClideTheme.of / .controllerOf inherited-widget lookups, the alpha
+/// path in _composite, ContrastFailure.toString, ThemeLoader's
+/// non-map / fromFile paths, and the Palette.names / SemanticRoles.roles
+/// getters.
+library;
+
+import 'dart:io';
+import 'dart:ui';
+
+import 'package:clide/kernel/kernel.dart';
+import 'package:clide/kernel/src/theme/contrast.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('ClideTheme inherited-widget lookups', () {
+    testWidgets('of() returns the current theme data when wrapped', (tester) async {
+      final controller = ThemeController(
+        bundled: [
+          ThemeDefinition(
+            name: 't',
+            displayName: 't',
+            dark: true,
+            palette: Palette(const {
+              'primary': Color(0xFF000000),
+              'foreground': Color(0xFFFFFFFF),
+              'background': Color(0xFF000000),
+              'surface': Color(0xFF111111),
+              'panel': Color(0xFF222222),
+              'accent': Color(0xFFFF00FF),
+              'success': Color(0xFF00FF00),
+              'warning': Color(0xFFFFFF00),
+              'error': Color(0xFFFF0000),
+            }),
+          ),
+        ],
+        initialName: 't',
+      );
+      addTearDown(controller.dispose);
+      late ClideThemeData captured;
+      await tester.pumpWidget(Directionality(
+        textDirection: TextDirection.ltr,
+        child: ClideTheme(
+          controller: controller,
+          child: Builder(builder: (ctx) {
+            captured = ClideTheme.of(ctx);
+            return const SizedBox();
+          }),
+        ),
+      ));
+      expect(captured, isNotNull);
+    });
+
+    testWidgets('of() throws when no ClideTheme ancestor', (tester) async {
+      late Object captured;
+      await tester.pumpWidget(Directionality(
+        textDirection: TextDirection.ltr,
+        child: Builder(builder: (ctx) {
+          try {
+            ClideTheme.of(ctx);
+          } catch (e) {
+            captured = e;
+          }
+          return const SizedBox();
+        }),
+      ));
+      expect(captured, isA<FlutterError>());
+    });
+
+    testWidgets('controllerOf() returns the wrapped controller', (tester) async {
+      final controller = ThemeController(
+        bundled: [
+          ThemeDefinition(
+            name: 't',
+            displayName: 't',
+            dark: true,
+            palette: Palette(const {
+              'primary': Color(0xFF000000),
+              'foreground': Color(0xFFFFFFFF),
+              'background': Color(0xFF000000),
+              'surface': Color(0xFF111111),
+              'panel': Color(0xFF222222),
+              'accent': Color(0xFFFF00FF),
+              'success': Color(0xFF00FF00),
+              'warning': Color(0xFFFFFF00),
+              'error': Color(0xFFFF0000),
+            }),
+          ),
+        ],
+        initialName: 't',
+      );
+      addTearDown(controller.dispose);
+      late ThemeController captured;
+      await tester.pumpWidget(Directionality(
+        textDirection: TextDirection.ltr,
+        child: ClideTheme(
+          controller: controller,
+          child: Builder(builder: (ctx) {
+            captured = ClideTheme.controllerOf(ctx);
+            return const SizedBox();
+          }),
+        ),
+      ));
+      expect(captured, same(controller));
+    });
+
+    testWidgets('controllerOf() throws when no ClideTheme ancestor', (tester) async {
+      late Object captured;
+      await tester.pumpWidget(Directionality(
+        textDirection: TextDirection.ltr,
+        child: Builder(builder: (ctx) {
+          try {
+            ClideTheme.controllerOf(ctx);
+          } catch (e) {
+            captured = e;
+          }
+          return const SizedBox();
+        }),
+      ));
+      expect(captured, isA<FlutterError>());
+    });
+  });
+
+  group('contrast tail paths', () {
+    test('contrastRatio composites partially-transparent colours onto the neutral grey', () {
+      // alpha < 0.999 → _composite mix branch.
+      const semiRed = Color.from(alpha: 0.5, red: 1.0, green: 0.0, blue: 0.0);
+      const opaqueBlack = Color(0xFF000000);
+      final ratio = contrastRatio(semiRed, opaqueBlack);
+      // Mixed-with-grey red on black still produces a finite ratio > 1.
+      expect(ratio, greaterThan(1.0));
+      expect(ratio, lessThan(21.0));
+    });
+
+    test('ContrastFailure.toString embeds the pair name, ratio, and minimum', () {
+      const failure = ContrastFailure(
+        pair: ContrastPair(
+          name: 'global.text_on_background',
+          foreground: Color(0xFF888888),
+          background: Color(0xFF7F7F7F),
+        ),
+        ratio: 1.23,
+        minimum: 4.5,
+      );
+      final s = failure.toString();
+      expect(s, contains('global.text_on_background'));
+      expect(s, contains('1.23'));
+      expect(s, contains('4.5'));
+    });
+  });
+
+  group('ThemeLoader error + file paths', () {
+    test('fromYamlString throws when the root is not a map', () {
+      expect(
+        () => const ThemeLoader().fromYamlString('- this\n- is\n- a list'),
+        throwsA(isA<FormatException>()),
+      );
+    });
+
+    test('fromFile loads the same content as fromYamlString', () async {
+      final tmp = await File.fromUri(
+        Uri.file('${Directory.systemTemp.path}/clide-theme-${DateTime.now().microsecondsSinceEpoch}.yaml'),
+      ).create();
+      addTearDown(() async {
+        if (tmp.existsSync()) await tmp.delete();
+      });
+      await tmp.writeAsString('''
+name: tmp
+palette:
+  foreground: "#FFFFFF"
+  background: "#000000"
+  primary: "#FF00FF"
+  accent: "#00FFFF"
+  surface: "#111111"
+  panel: "#222222"
+  success: "#00FF00"
+  warning: "#FFFF00"
+  error: "#FF0000"
+''');
+      final def = await const ThemeLoader().fromFile(tmp);
+      expect(def.name, 'tmp');
+      expect(def.palette.lookup('foreground')?.toARGB32(), 0xFFFFFFFF);
+    });
+  });
+
+  group('Palette / SemanticRoles iterables', () {
+    test('Palette.names yields every registered colour key', () {
+      final p = Palette(const {
+        'primary': Color(0xFF000000),
+        'accent': Color(0xFFFFFFFF),
+      });
+      expect(p.names, containsAll(['primary', 'accent']));
+    });
+
+    test('SemanticRoles.roles yields every registered role key', () {
+      final s = SemanticRoles(const {
+        'text': Color(0xFFFFFFFF),
+        'background': Color(0xFF000000),
+      });
+      expect(s.roles, containsAll(['text', 'background']));
+    });
+  });
+}