fix(mobile): prevent iOS status bar scroll to top during transitions (#30717)

mobile/lib/main.dart

@@ -277,7 +277,7 @@ class ImmichAppState extends ConsumerState<ImmichApp> with WidgetsBindingObserve
         ),
         routerConfig: router.config(
           deepLinkBuilder: _deepLinkBuilder,
-          navigatorObservers: () => [AppNavigationObserver(ref: ref)],
+          navigatorObservers: () => [AppNavigationObserver(ref: ref), TransitioningRouteObserver()],
         ),
       ),
     );

mobile/lib/presentation/widgets/timeline/timeline.widget.dart

@@ -26,6 +26,7 @@ import 'package:immich_mobile/providers/infrastructure/readonly_mode.provider.da
 import 'package:immich_mobile/providers/infrastructure/settings.provider.dart';
 import 'package:immich_mobile/providers/infrastructure/timeline.provider.dart';
 import 'package:immich_mobile/providers/timeline/multiselect.provider.dart';
+import 'package:immich_mobile/routing/app_navigation_observer.dart';
 import 'package:immich_mobile/widgets/common/immich_sliver_app_bar.dart';
 import 'package:immich_mobile/widgets/common/mesmerizing_sliver_app_bar.dart';
 import 'package:immich_mobile/widgets/common/selection_sliver_app_bar.dart';
@@ -190,7 +191,14 @@ class _SliverTimelineState extends ConsumerState<_SliverTimeline> with WidgetsBi
     // may be in a background tab. In either case, `handleStatusBarTap()` still fires
     // Make sure the timeline is the primary route before scrolling to the top
     final routeData = context.findAncestorWidgetOfExactType<RouteDataScope>()?.routeData;
-    if (ModalRoute.of(context)?.isCurrent == true && routeData?.isActive == true) {
+    // The tap is generated async, so it can arrive after a route pop has started (due to a back button or similar)
+    // Check if route is alive and not exiting before taking action
+    final observers = Navigator.maybeOf(context)?.widget.observers ?? const <NavigatorObserver>[];
+    final isRouteTransitioning = observers.whereType<TransitioningRouteObserver>().any(
+      (observer) => observer.hasTransitioningRoute,
+    );
+
+    if (ModalRoute.of(context)?.isCurrent == true && routeData?.isActive == true && !isRouteTransitioning) {
       _scrollToTop();
     }
   }

mobile/lib/routing/app_navigation_observer.dart

@@ -30,3 +30,22 @@ class AppNavigationObserver extends AutoRouterObserver {
     ref.invalidate(isAssetViewerOpenProvider);
   }
 }
+
+/// Tracks routes that are undergoing a pop transition
+class TransitioningRouteObserver extends NavigatorObserver {
+  int _transitioningRoutes = 0;
+
+  /// Whether a "popping" route is still on screen
+  bool get hasTransitioningRoute => _transitioningRoutes > 0;
+
+  @override
+  void didPop(Route route, Route? previousRoute) {
+    if (route is! TransitionRoute) {
+      return;
+    }
+
+    _transitioningRoutes += 1;
+    // Transition completed and route disposed
+    unawaited(route.completed.whenComplete(() => _transitioningRoutes -= 1));
+  }
+}

mobile/test/presentation/widgets/timeline/timeline_scroll_to_top_test.dart

@@ -13,6 +13,7 @@ import 'package:immich_mobile/domain/services/timeline.service.dart';
 import 'package:immich_mobile/presentation/widgets/timeline/timeline.widget.dart';
 import 'package:immich_mobile/providers/infrastructure/settings.provider.dart';
 import 'package:immich_mobile/providers/infrastructure/timeline.provider.dart';
+import 'package:immich_mobile/routing/app_navigation_observer.dart';
 
 import '../../../fixtures/asset.stub.dart';
 
@@ -62,7 +63,9 @@ void main() {
           timelineServiceProvider.overrideWithValue(service),
           appConfigProvider.overrideWithValue(const AppConfig()),
         ],
-        child: MaterialApp.router(routerConfig: router.config()),
+        child: MaterialApp.router(
+          routerConfig: router.config(navigatorObservers: () => [TransitioningRouteObserver()]),
+        ),
       ),
     );
     // Segment stream resolves
@@ -96,9 +99,14 @@ void main() {
     await tester.pumpAndSettle();
     expect(position.pixels, initialScrolledPosition, reason: 'ignored while behind a pushed route');
 
-    // Once the timeline is visible, taps on the status bar should scroll to the top
+    // The tap is async, so it can arrive while a pushed route is transitioning to popped
-    await router.maybePop();
+    unawaited(router.maybePop());
+    await tester.pump();
+    await tapStatusBar();
     await tester.pumpAndSettle();
+    expect(position.pixels, initialScrolledPosition, reason: 'ignored while the pushed route pops');
+
+    // Once the timeline is visible, taps on the status bar should scroll to the top
     await tapStatusBar();
     await tester.pumpAndSettle();
     expect(position.pixels, 0, reason: 'scrolls the foreground timeline');