add slash-command typeahead to the Claude composer

Typing a slash — anywhere in the message, not just at the start — opens
an anchored typeahead listing matching commands and skills from
ClaudeConfig's slash list. Arrow keys move the selection, Enter/Tab
completes (inserting "/command "), Escape dismisses; with the popup
closed, Enter still submits and Tab still traverses. The recognition,
filtering, and completion are pure functions (slash_commands.dart) so
they're cheaply unit-tested; the overlay is a no-Material
CompositedTransformFollower keyed off the field's focus node.

T-152.

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

test/builtin/claude/claude_composer_test.dart

@@ -130,6 +130,84 @@ void main() {
       expect(find.text('notes.txt'), findsNothing);
     });
 
+    Future<List<String>> pumpWithCommands(
+      WidgetTester tester,
+      List<String> commands,
+    ) async {
+      final submitted = <String>[];
+      await tester.pumpWidget(harness(
+        f,
+        ClaudeComposer(
+          onSubmit: submitted.add,
+          slashCommandsResolver: () => commands,
+        ),
+      ));
+      return submitted;
+    }
+
+    testWidgets('typing a slash opens the typeahead with matching commands', (tester) async {
+      await pumpWithCommands(tester, ['model', 'memory', 'clear']);
+      await tester.enterText(find.byType(EditableText), '/m');
+      await tester.pump();
+
+      expect(find.text('/model'), findsOneWidget);
+      expect(find.text('/memory'), findsOneWidget);
+      expect(find.text('/clear'), findsNothing);
+    });
+
+    testWidgets('an inline slash (mid-message) also opens the typeahead', (tester) async {
+      await pumpWithCommands(tester, ['clear', 'compact']);
+      await tester.enterText(find.byType(EditableText), 'hey /cl');
+      await tester.pump();
+      expect(find.text('/clear'), findsOneWidget);
+    });
+
+    testWidgets('arrow-down + Enter completes the selected command (no submit)', (tester) async {
+      final submitted = await pumpWithCommands(tester, ['model', 'memory']);
+      await tester.enterText(find.byType(EditableText), '/m'); // → [memory, model]
+      await tester.pump();
+
+      await tester.sendKeyEvent(LogicalKeyboardKey.arrowDown); // select 'model'
+      await tester.pump();
+      await tester.sendKeyEvent(LogicalKeyboardKey.enter);
+      await tester.pump();
+
+      expect(tester.widget<EditableText>(find.byType(EditableText)).controller.text, '/model ');
+      expect(submitted, isEmpty, reason: 'Enter completes, it does not submit, while the popup is open');
+      expect(find.text('/memory'), findsNothing, reason: 'popup closes after completion');
+    });
+
+    testWidgets('Tab completes the top suggestion', (tester) async {
+      await pumpWithCommands(tester, ['clear', 'compact']);
+      await tester.enterText(find.byType(EditableText), '/cle');
+      await tester.pump();
+      await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+      await tester.pump();
+      expect(tester.widget<EditableText>(find.byType(EditableText)).controller.text, '/clear ');
+    });
+
+    testWidgets('Escape dismisses the typeahead', (tester) async {
+      await pumpWithCommands(tester, ['model']);
+      await tester.enterText(find.byType(EditableText), '/mo');
+      await tester.pump();
+      expect(find.text('/model'), findsOneWidget);
+
+      await tester.sendKeyEvent(LogicalKeyboardKey.escape);
+      await tester.pump();
+      expect(find.text('/model'), findsNothing);
+    });
+
+    testWidgets('with the popup closed, Enter still submits', (tester) async {
+      final submitted = await pumpWithCommands(tester, ['model']);
+      await tester.enterText(find.byType(EditableText), 'plain message');
+      await tester.pump();
+      expect(find.text('/model'), findsNothing);
+
+      await tester.sendKeyEvent(LogicalKeyboardKey.enter);
+      await tester.pump();
+      expect(submitted, ['plain message']);
+    });
+
     testWidgets('remove × cancels the attachment before send', (tester) async {
       final submitted = <String>[];
       await tester.pumpWidget(harness(

test/builtin/claude/slash_commands_test.dart

@@ -35,4 +35,57 @@ void main() {
       expect(isKnownSlashCommand('/clear\nand more', {'clear'}), isFalse);
     });
   });
+
+  group('activeSlashQuery', () {
+    test('matches a slash token at the cursor, including inline', () {
+      expect(activeSlashQuery('/mod', 4), const SlashQuery(start: 0, query: 'mod'));
+      expect(activeSlashQuery('go /mo', 6), const SlashQuery(start: 3, query: 'mo'));
+      expect(activeSlashQuery('/', 1), const SlashQuery(start: 0, query: ''));
+    });
+
+    test('no match for paths, post-space, or non-slash runs', () {
+      expect(activeSlashQuery('a/b', 3), isNull); // slash mid-token (path)
+      expect(activeSlashQuery('/model sonnet', 13), isNull); // closed after space
+      expect(activeSlashQuery('hello', 5), isNull);
+      expect(activeSlashQuery('/model ', 7), isNull); // cursor right after space
+    });
+
+    test('uses the cursor, not the end of text', () {
+      // Cursor sits right after "/mo" inside "/model".
+      expect(activeSlashQuery('/model', 3), const SlashQuery(start: 0, query: 'mo'));
+    });
+  });
+
+  group('filterSlashCommands', () {
+    const commands = ['model', 'memory', 'clear', 'compact', 'context'];
+
+    test('prefix-filters case-insensitively and sorts', () {
+      expect(filterSlashCommands('co', commands), ['compact', 'context']);
+      expect(filterSlashCommands('M', commands), ['memory', 'model']);
+    });
+
+    test('empty query returns all (sorted, capped)', () {
+      expect(filterSlashCommands('', commands, limit: 3), ['clear', 'compact', 'context']);
+    });
+
+    test('de-duplicates', () {
+      expect(filterSlashCommands('p', ['pql', 'pql', 'plan']), ['plan', 'pql']);
+    });
+  });
+
+  group('completeSlash', () {
+    test('replaces the token with /command and a trailing space', () {
+      const q = SlashQuery(start: 0, query: 'mo');
+      final r = completeSlash('/mo', q, 'model');
+      expect(r.text, '/model ');
+      expect(r.cursor, 7);
+    });
+
+    test('completes an inline token without disturbing surrounding text', () {
+      const q = SlashQuery(start: 3, query: 'mo');
+      final r = completeSlash('go /mo now', q, 'model');
+      expect(r.text, 'go /model  now');
+      expect(r.cursor, 10);
+    });
+  });
 }