refactor(widgets): name SheetHandle's container key explicitly

Replace the constructor that accepted `key` and forwarded it to the
inner Container while passing null to super. Swallowing `key` made
SheetHandle(key: k) silently unkeyed, which is surprising for a shared
widget. An explicit `handleKey` keeps the three drag-handle test
assertions matching a single Container and leaves `key` behaving
normally.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017B31wKKL578bV18hcpXyE2

Author: claude

lib/widgets/festival_menu_sheets.dart

@@ -91,7 +91,7 @@ class FestivalSelectorSheet extends StatelessWidget {
         mainAxisSize: MainAxisSize.min,
         crossAxisAlignment: CrossAxisAlignment.start,
         children: [
-          const SheetHandle(key: Key('festival_selector_drag_handle')),
+          const SheetHandle(handleKey: Key('festival_selector_drag_handle')),
           const SizedBox(height: 16),
           Row(
             children: [
@@ -449,7 +449,7 @@ class SettingsSheet extends StatelessWidget {
         mainAxisSize: MainAxisSize.min,
         crossAxisAlignment: CrossAxisAlignment.start,
         children: [
-          const SheetHandle(key: Key('settings_sheet_drag_handle')),
+          const SheetHandle(handleKey: Key('settings_sheet_drag_handle')),
           const SizedBox(height: 16),
           Text('Settings', style: theme.textTheme.titleLarge),
           const SizedBox(height: 16),
@@ -500,7 +500,7 @@ class ThemeSelectorSheet extends StatelessWidget {
         mainAxisSize: MainAxisSize.min,
         crossAxisAlignment: CrossAxisAlignment.start,
         children: [
-          const SheetHandle(key: Key('theme_selector_sheet_drag_handle')),
+          const SheetHandle(handleKey: Key('theme_selector_sheet_drag_handle')),
           const SizedBox(height: 16),
           Text('Theme', style: theme.textTheme.titleLarge),
           const SizedBox(height: 16),

lib/widgets/sheet_handle.dart

@@ -3,21 +3,22 @@ import 'package:flutter/material.dart';
 /// Drag handle shown at the top of every modal bottom sheet in this app
 /// (filter sheets, festival selector, settings, theme selector).
 ///
-/// The key passed to this widget is applied to the inner [Container] rather
-/// than to [SheetHandle] itself, so callers that key the drag handle for
-/// tests (`SheetHandle(key: Key('some_drag_handle'))`) can keep finding a
-/// [Container] with that key — matching the pre-refactor widget tree where
-/// the key lived directly on the hand-rolled `Container`.
+/// [handleKey] is applied to the inner [Container] rather than to this widget,
+/// so callers that key the drag handle for tests keep finding a [Container]
+/// with that key — matching the pre-refactor widget tree, where the key lived
+/// directly on the hand-rolled `Container`. Keying the widget itself via [key]
+/// remains available and behaves normally.
 class SheetHandle extends StatelessWidget {
-  const SheetHandle({Key? key}) : _handleKey = key, super(key: null);
+  const SheetHandle({this.handleKey, super.key});
 
-  final Key? _handleKey;
+  /// Key applied to the inner container, for tests locating the handle.
+  final Key? handleKey;
 
   @override
   Widget build(BuildContext context) {
     return Center(
       child: Container(
-        key: _handleKey,
+        key: handleKey,
         width: 32,
         height: 4,
         decoration: BoxDecoration(

test/widgets/sheet_handle_test.dart

@@ -34,13 +34,17 @@ void main() {
       );
     });
 
-    testWidgets('honours a passed key on the inner container', (tester) async {
+    testWidgets('applies handleKey to the inner container', (tester) async {
       await tester.pumpWidget(
         const MaterialApp(
-          home: Scaffold(body: SheetHandle(key: Key('my_drag_handle'))),
+          home: Scaffold(body: SheetHandle(handleKey: Key('my_drag_handle'))),
         ),
       );
 
+      // Exactly one match: the key lands on the Container only, never on the
+      // SheetHandle itself, so tester.widget<Container>() stays unambiguous.
+      expect(find.byKey(const Key('my_drag_handle')), findsOneWidget);
+
       final container = tester.widget<Container>(
         find.byKey(const Key('my_drag_handle')),
       );
@@ -50,6 +54,20 @@ void main() {
       );
     });
 
+    testWidgets('keys the widget itself normally via key', (tester) async {
+      await tester.pumpWidget(
+        const MaterialApp(
+          home: Scaffold(body: SheetHandle(key: Key('handle_widget'))),
+        ),
+      );
+
+      expect(find.byKey(const Key('handle_widget')), findsOneWidget);
+      expect(
+        tester.widget(find.byKey(const Key('handle_widget'))),
+        isA<SheetHandle>(),
+      );
+    });
+
     testWidgets('uses onSurfaceVariant from the current theme', (tester) async {
       final lightTheme = buildAppTheme(Brightness.light);