lock in slash typeahead hyphen + Tab-accept behaviour (T-278)

Both T-278 issues — typing '-' breaking the list, and flaky Tab-to-complete —
were resolved by the D-88 ClideTypeahead migration (T-286): the popover now
narrows live as you type (ValueNotifier-bridged suggestions) and the field keeps
focus (captureFocus:false), so '-' filters normally and Tab reliably accepts the
highlight. Add regression coverage: hyphenated queries in slash_commands_test and
a composer widget test that types through a hyphen then Tab-completes.

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

test/builtin/claude/claude_composer_test.dart

@@ -191,6 +191,28 @@ void main() {
       expect(tester.widget<EditableText>(find.byType(EditableText)).controller.text, '/clear ');
     });
 
+    testWidgets('a hyphenated command keeps filtering through the dash and Tab completes it (T-278)', (tester) async {
+      await pumpWithCommands(tester, ['add-dir', 'add-context', 'model']);
+      await tester.enterText(find.byType(EditableText), '/add-');
+      await tester.pump();
+      await tester.pump(); // ClideTypeahead inserts the popover post-frame
+      expect(find.text('/add-dir'), findsOneWidget);
+      expect(find.text('/add-context'), findsOneWidget);
+      expect(find.text('/model'), findsNothing);
+
+      // Typing further through the hyphen narrows the list (it does not empty it).
+      await tester.enterText(find.byType(EditableText), '/add-d');
+      await tester.pump();
+      await tester.pump();
+      expect(find.text('/add-dir'), findsOneWidget);
+      expect(find.text('/add-context'), findsNothing);
+
+      // Tab reliably accepts the highlighted suggestion.
+      await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+      await tester.pump();
+      expect(tester.widget<EditableText>(find.byType(EditableText)).controller.text, '/add-dir ');
+    });
+
     testWidgets('Escape dismisses the typeahead', (tester) async {
       await pumpWithCommands(tester, ['model']);
       await tester.enterText(find.byType(EditableText), '/mo');

test/builtin/claude/slash_commands_test.dart

@@ -69,6 +69,12 @@ void main() {
       // Cursor sits right after "/mo" inside "/model".
       expect(activeSlashQuery('/model', 3), const SlashQuery(start: 0, query: 'mo'));
     });
+
+    test('hyphens are part of the command token, not a boundary (T-278)', () {
+      expect(activeSlashQuery('/add-dir', 8), const SlashQuery(start: 0, query: 'add-dir'));
+      expect(activeSlashQuery('/add-', 5), const SlashQuery(start: 0, query: 'add-'));
+      expect(activeSlashQuery('go /output-st', 13), const SlashQuery(start: 3, query: 'output-st'));
+    });
   });
 
   group('filterSlashCommands', () {
@@ -86,6 +92,14 @@ void main() {
     test('de-duplicates', () {
       expect(filterSlashCommands('p', ['pql', 'pql', 'plan']), ['plan', 'pql']);
     });
+
+    test('keeps filtering through a hyphen in the query (T-278)', () {
+      const hyphenated = ['add-dir', 'add-context', 'agents', 'output-style'];
+      // Typing the '-' narrows rather than emptying the list.
+      expect(filterSlashCommands('add', hyphenated), ['add-context', 'add-dir']);
+      expect(filterSlashCommands('add-', hyphenated), ['add-context', 'add-dir']);
+      expect(filterSlashCommands('add-d', hyphenated), ['add-dir']);
+    });
   });
 
   group('completeSlash', () {