refactor(navigation): centralize sidebar focus

lib/mixins/tab_navigation_mixin.dart

@@ -84,7 +84,7 @@ mixin TabNavigationMixin<T extends StatefulWidget> on State<T>, TickerProviderSt
   }
 
   void onTabBarBack() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   /// Shared tab chip builder — eliminates duplication between screens.

lib/navigation/main_screen_scope.dart

@@ -56,6 +56,11 @@ class MainScreenFocusScope extends InheritedModel<MainScreenScopeAspect> {
     return context.getElementForInheritedWidgetOfExactType<MainScreenFocusScope>()?.widget as MainScreenFocusScope?;
   }
 
+  /// Focuses the sidebar without registering an inherited dependency.
+  static void focusSidebarOf(BuildContext context) {
+    of(context, listen: false)?.focusSidebar();
+  }
+
   static MainScreenFocusScope? _dependOn(BuildContext context, MainScreenScopeAspect aspect) {
     return InheritedModel.inheritFrom<MainScreenFocusScope>(context, aspect: aspect);
   }

lib/screens/discover_screen.dart

@@ -362,7 +362,7 @@ class _DiscoverScreenState extends State<DiscoverScreen>
 
   /// Navigate focus to the sidebar
   void _navigateToSidebar() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   @override

lib/screens/downloads/downloads_screen.dart

@@ -220,7 +220,7 @@ class DownloadsScreenState extends State<DownloadsScreen>
                             },
                             onCancel: downloadProvider.cancelDownload,
                             onDelete: downloadProvider.deleteDownload,
-                            onNavigateLeft: () => MainScreenFocusScope.of(context, listen: false)?.focusSidebar(),
+                            onNavigateLeft: () => MainScreenFocusScope.focusSidebarOf(context),
                             onBack: focusTabBar,
                             suppressAutoFocus: suppressAutoFocus,
                           );
@@ -287,7 +287,7 @@ class _DownloadsGridContentState extends State<_DownloadsGridContent> {
 
   /// Navigate focus to the sidebar
   void _navigateToSidebar() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   @override

lib/screens/explore_screen.dart

@@ -133,7 +133,7 @@ class ExploreScreenState extends State<ExploreScreen>
   }
 
   void _navigateToSidebar() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   static IconData _rowIcon(CatalogRowId row) => switch (row) {

lib/screens/libraries/tabs/library_browse_tab.dart

@@ -1198,7 +1198,7 @@ class _LibraryBrowseTabState extends BaseLibraryTabState<MediaItem, LibraryBrows
 
   /// Navigate focus to the sidebar
   void _navigateToSidebar() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   /// Navigate focus to the alpha jump bar

lib/screens/libraries/tabs/library_collections_tab.dart

@@ -252,7 +252,7 @@ class _LibraryCollectionsTabState extends BaseLibraryTabState<MediaItem, Library
   }
 
   void _navigateToSidebar() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   @override

lib/screens/libraries/tabs/library_playlists_tab.dart

@@ -212,7 +212,7 @@ class _LibraryPlaylistsTabState extends BaseLibraryTabState<MediaPlaylist, Libra
   }
 
   void _navigateToSidebar() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   @override

lib/screens/libraries/tabs/library_recommended_tab.dart

@@ -317,7 +317,7 @@ class _LibraryRecommendedTabState extends BaseLibraryTabState<MediaHub, LibraryR
 
   /// Navigate focus to the sidebar
   void _navigateToSidebar() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   // Extra top padding for focus decoration (scale + border extends beyond item bounds)

lib/screens/search_screen.dart

@@ -148,7 +148,7 @@ class _SearchScreenState extends State<SearchScreen>
 
   /// Navigate focus to the sidebar
   void _navigateToSidebar() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   Widget _buildResultsList(BuildContext context) {

lib/screens/settings/settings_screen.dart

@@ -117,7 +117,7 @@ class _SettingsScreenState extends State<SettingsScreen> with FocusableTab, Moun
   }
 
   void _navigateToSidebar() {
-    MainScreenFocusScope.of(context, listen: false)?.focusSidebar();
+    MainScreenFocusScope.focusSidebarOf(context);
   }
 
   KeyEventResult _handleKeyEvent(FocusNode _, KeyEvent event) {

test/navigation/main_screen_scope_test.dart

@@ -0,0 +1,88 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:plezy/navigation/main_screen_scope.dart';
+
+void main() {
+  testWidgets('focusSidebarOf invokes the scope callback', (tester) async {
+    var focusCalls = 0;
+    late BuildContext childContext;
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: MainScreenFocusScope(
+          focusSidebar: () => focusCalls++,
+          focusContent: () {},
+          isSidebarFocused: false,
+          sideNavigationWidth: 0,
+          child: Builder(
+            builder: (context) {
+              childContext = context;
+              return const SizedBox.shrink();
+            },
+          ),
+        ),
+      ),
+    );
+
+    MainScreenFocusScope.focusSidebarOf(childContext);
+
+    expect(focusCalls, 1);
+  });
+
+  testWidgets('focusSidebarOf is a no-op without a scope', (tester) async {
+    late BuildContext childContext;
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Builder(
+          builder: (context) {
+            childContext = context;
+            return const SizedBox.shrink();
+          },
+        ),
+      ),
+    );
+
+    expect(() => MainScreenFocusScope.focusSidebarOf(childContext), returnsNormally);
+  });
+
+  testWidgets('focusSidebarOf does not register an inherited dependency', (tester) async {
+    var isSidebarFocused = false;
+    var childBuilds = 0;
+    var focusCalls = 0;
+    late StateSetter rebuildScope;
+    final child = Builder(
+      builder: (context) {
+        childBuilds++;
+        MainScreenFocusScope.focusSidebarOf(context);
+        return const SizedBox.shrink();
+      },
+    );
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: StatefulBuilder(
+          builder: (context, setState) {
+            rebuildScope = setState;
+            return MainScreenFocusScope(
+              focusSidebar: () => focusCalls++,
+              focusContent: () {},
+              isSidebarFocused: isSidebarFocused,
+              sideNavigationWidth: 0,
+              child: child,
+            );
+          },
+        ),
+      ),
+    );
+
+    expect(childBuilds, 1);
+    expect(focusCalls, 1);
+
+    rebuildScope(() => isSidebarFocused = true);
+    await tester.pump();
+
+    expect(childBuilds, 1);
+    expect(focusCalls, 1);
+  });
+}