catch and correct possible bad values for lat/lon, add tests

lib/widgets/map_view.dart

@@ -26,9 +26,12 @@ import 'node_limit_indicator.dart';
 import 'proximity_alert_banner.dart';
 import '../dev_config.dart';
 import '../services/proximity_alert_service.dart';
+import '../services/coordinate_validation.dart';
 import 'sheet_aware_map.dart';
+
 import 'custom_scale_bar.dart';
 
+
 class MapView extends StatefulWidget {
   final AnimatedMapController controller;
   const MapView({
@@ -80,6 +83,15 @@ class MapViewState extends State<MapView> {
   
   // Track map center to clear queue on significant panning
   LatLng? _lastCenter;
+
+  // Track the last known-good (finite, in-range) camera center/zoom so we
+  // can self-heal if the camera ever gets pushed into a degenerate state
+  // (e.g. by an edge case in flutter_map's internal gesture-to-camera
+  // pipeline). This mirrors the validation used for persisted map position
+  // in MapPositionManager, applied to the *live* camera as well.
+  LatLng? _lastValidCenter;
+  double? _lastValidZoom;
+
   
   // State for proximity alert banner
   bool _showProximityBanner = false;
@@ -275,6 +287,29 @@ class MapViewState extends State<MapView> {
     return (!appState.offlineMode && appState.isInSearchMode) ? 60.0 : 0.0;
   }
 
+  /// Get a known-good fallback location for [initialCenter], preferring a
+  /// validated GPS location, then a validated persisted position, then a
+  /// hardcoded default. GpsController already validates incoming fixes, but
+  /// this extra check keeps launch resilient even if that guard is ever
+  /// bypassed (e.g. future refactor).
+  LatLng get _safeInitialCenter {
+    final gpsLocation = _gpsController.currentLocation;
+    if (gpsLocation != null &&
+        isValidCoordinate(gpsLocation.latitude) &&
+        isValidCoordinate(gpsLocation.longitude)) {
+      return gpsLocation;
+    }
+    final persisted = _positionManager.initialLocation;
+    if (persisted != null &&
+        isValidCoordinate(persisted.latitude) &&
+        isValidCoordinate(persisted.longitude)) {
+      return persisted;
+    }
+    return LatLng(37.7749, -122.4194);
+  }
+
+
+
 
   @override
   void didUpdateWidget(covariant MapView oldWidget) {
@@ -414,18 +449,55 @@ class MapViewState extends State<MapView> {
               key: ValueKey('map_${appState.selectedTileProvider?.id ?? 'none'}_${appState.selectedTileType?.id ?? 'none'}_${appState.offlineMode}_${_tileManager.mapRebuildKey}'),
               mapController: _controller.mapController,
               options: MapOptions(
-              initialCenter: _gpsController.currentLocation ?? _positionManager.initialLocation ?? LatLng(37.7749, -122.4194),
+              initialCenter: _safeInitialCenter,
             initialZoom: _positionManager.initialZoom ?? 15,
+
             minZoom: 1.0,
             maxZoom: (appState.selectedTileType?.maxZoom ?? 18).toDouble(),
             interactionOptions: _interactionManager.getInteractionOptions(editSession),
             onPositionChanged: (pos, gesture) {
+              // Self-heal if the camera has been pushed into a degenerate
+              // state (non-finite or wildly out-of-range center/zoom). This
+              // has been observed to occur silently during ordinary panning
+              // (no crash, no console output) — likely an edge case in
+              // flutter_map's internal gesture-to-camera math — leaving the
+              // map showing a blank grey view with no tiles or markers,
+              // since every subsequent gesture computes its new position as
+              // a delta from the already-broken center. Snap back to the
+              // last known-good position the moment this is detected rather
+              // than requiring the user to discover the GPS button "fixes"
+              // it (which works only because it supplies a fresh valid
+              // destination).
+              if (!isValidCoordinate(pos.center.latitude) ||
+                  !isValidCoordinate(pos.center.longitude) ||
+                  !isValidZoom(pos.zoom)) {
+
+                debugPrint(
+                  '[MapView] Detected invalid camera position '
+                  '(lat=${pos.center.latitude}, lng=${pos.center.longitude}, zoom=${pos.zoom}) '
+                  '- snapping back to last known-good position',
+                );
+                final recoveryCenter = _lastValidCenter ?? _safeInitialCenter;
+                final recoveryZoom = _lastValidZoom ?? (_positionManager.initialZoom ?? 15.0);
+                WidgetsBinding.instance.addPostFrameCallback((_) {
+                  try {
+                    _controller.mapController.move(recoveryCenter, recoveryZoom);
+                  } catch (e) {
+                    debugPrint('[MapView] Failed to recover camera position: $e');
+                  }
+                });
+                return; // Don't process this invalid position further
+              }
+              _lastValidCenter = pos.center;
+              _lastValidZoom = pos.zoom;
+
               setState(() {}); // Instant UI update for zoom, etc.
               if (gesture) {
                 widget.onUserGesture();
               }
               
               // Enforce minimum zoom level for add/edit node sheets (but not tag sheet)
+
               if ((session != null || editSession != null) && pos.zoom < kMinZoomForNodeEditingSheets) {
                 // User tried to zoom out below minimum - snap back to minimum zoom
                 _controller.animateTo(