Fix late background alerts and cache starvation

- Increase background refresh threshold: Raised the edge distance check in GpsController from 1000m to 2500m to guarantee new Overpass data is fetched well before the user drives out of the cached bounding box.

- Fix bounding box race condition: Added await to the background fetch handler in MapView so tracking bounds only shift forward after the network request successfully finishes.

- Make debounced fetches awaitable: Refactored fetchAndUpdate in NodeProviderWithCache to return a Future<void> using a Completer, bridging the 400ms debounce timer.

- Prevent hanging futures: Added state checks for _activeCompleter to instantly resolve canceled network requests during rapid map panning, preventing fatal StateError crashes and infinite UI hangs.

lib/widgets/map/gps_controller.dart

@@ -333,9 +333,9 @@ class GpsController {
       final minDist = [northDist, southDist, eastDist, westDist].reduce((a, b) => a < b ? a : b);
 
       // Debug 2: Print the closest distance to the edge
-      debugPrint('[GpsController-Background] Closest edge distance: ${minDist.toStringAsFixed(1)}m (Threshold: 1000m)');
+      debugPrint('[GpsController-Background] Closest edge distance: ${minDist.toStringAsFixed(1)}m (Threshold: 2500m)');
 
-      if (minDist < 1000) {
+      if (minDist < 2500) {
         debugPrint('[GpsController-Background] Threshold crossed. Triggering refresh.');
         needsRefresh = true;
       }
@@ -554,4 +554,4 @@ class GpsController {
     _onMapMovedProgrammatically = null;
     _isUserInteracting = null;
   }
-}
+}

lib/widgets/map_view.dart

@@ -221,7 +221,7 @@ class MapViewState extends State<MapView> with WidgetsBindingObserver {
         if (!mounted) return;
         final appState = context.read<AppState>();
 
-        NodeProviderWithCache.instance.fetchAndUpdate(
+        await NodeProviderWithCache.instance.fetchAndUpdate(
           bounds: bounds,
           profiles: appState.enabledProfiles,
           uploadMode: appState.uploadMode,

lib/widgets/node_provider_with_cache.dart

@@ -17,6 +17,7 @@ class NodeProviderWithCache extends ChangeNotifier {
 
   final NodeDataManager _nodeDataManager = NodeDataManager();
   Timer? _debounceTimer;
+  Completer<void>? _activeCompleter;
 
   /// Get cached nodes for the given bounds, filtered by enabled profiles
   List<OsmNode> getCachedNodesForBounds(LatLngBounds bounds) {
@@ -34,14 +35,21 @@ class NodeProviderWithCache extends ChangeNotifier {
   }
 
   /// Fetch and update nodes for the given view, with debouncing for rapid map movement
-  void fetchAndUpdate({
+  Future<void> fetchAndUpdate({
     required LatLngBounds bounds,
     required List<NodeProfile> profiles,
     UploadMode uploadMode = UploadMode.production,
   }) {
     // Serve cached immediately
     notifyListeners();
-    
+
+    // Prevent hanging awaits by completing the previous request if it gets cancelled
+    if (_activeCompleter != null && !_activeCompleter!.isCompleted) {
+      _activeCompleter!.complete();
+    }
+
+    _activeCompleter = Completer<void>();
+
     // Debounce rapid panning/zooming
     _debounceTimer?.cancel();
     _debounceTimer = Timer(const Duration(milliseconds: 400), () async {
@@ -52,15 +60,21 @@ class NodeProviderWithCache extends ChangeNotifier {
           uploadMode: uploadMode,
           isUserInitiated: true,
         );
-        
+
         // Notify UI of new data
         notifyListeners();
-        
       } catch (e) {
         debugPrint('[NodeProviderWithCache] Node fetch failed: $e');
         // Cache already holds whatever is available for the view
+      } finally {
+        // Ensure we only complete if it hasn't been superseded by another call
+        if (_activeCompleter != null && !_activeCompleter!.isCompleted) {
+          _activeCompleter!.complete();
+        }
       }
     });
+
+    return _activeCompleter!.future;
   }
 
   /// Clear the cache and repopulate with pending nodes from upload queue
@@ -108,4 +122,4 @@ class NodeProviderWithCache extends ChangeNotifier {
     }
     return true;
   }
-}
+}