Fix GPS accuracy circle source/layer errors breaking WASD

Root cause: Uncaught "Source already exists" error in onGPSSuccess
was breaking execution flow before the WASD interval could start.

Fixes:
- Check if source exists before adding (use getSource instead of flag)
- Wrap layer/source removal in try-catch to handle edge cases
- Wrap source/layer creation in try-catch to prevent breaking execution
- Update existing source data instead of recreating when possible

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

index.html

@@ -6421,13 +6421,17 @@
                     gpsMarker.remove();  // MapLibre marker removal
                     gpsMarker = null;
                 }
-                if (gpsAccuracyCircle) {
-                    // Remove MapLibre layers and source
+                // Remove MapLibre GPS accuracy layers and source (always try, ignore errors)
+                try {
                     if (map.getLayer('gps-accuracy-fill')) map.removeLayer('gps-accuracy-fill');
+                } catch (e) { console.log('Could not remove gps-accuracy-fill:', e.message); }
+                try {
                     if (map.getLayer('gps-accuracy-stroke')) map.removeLayer('gps-accuracy-stroke');
+                } catch (e) { console.log('Could not remove gps-accuracy-stroke:', e.message); }
+                try {
                     if (map.getSource('gps-accuracy')) map.removeSource('gps-accuracy');
+                } catch (e) { console.log('Could not remove gps-accuracy source:', e.message); }
                 gpsAccuracyCircle = null;
-                }
 
                 // Sync test position to last known GPS location for seamless manual mode
                 if (userLocation) {
@@ -6563,9 +6567,16 @@
             }
 
             // Update or create accuracy circle (MapLibre GeoJSON version)
-            if (!gpsAccuracyCircle) {
-                // Create circle as GeoJSON using turf.js
             const circleGeoJSON = createCircleGeoJSON([lng, lat], accuracy);
+            const existingSource = map.getSource('gps-accuracy');
+
+            if (existingSource) {
+                // Update existing source
+                existingSource.setData(circleGeoJSON);
+                gpsAccuracyCircle = true;
+            } else {
+                // Create new source and layers
+                try {
                     map.addSource('gps-accuracy', {
                         type: 'geojson',
                         data: circleGeoJSON
@@ -6588,12 +6599,9 @@
                             'line-width': 1
                         }
                     });
-                gpsAccuracyCircle = true;  // Flag that source exists
-            } else {
-                // Update existing source
-                const source = map.getSource('gps-accuracy');
-                if (source) {
-                    source.setData(createCircleGeoJSON([lng, lat], accuracy));
+                    gpsAccuracyCircle = true;
+                } catch (e) {
+                    console.log('Error creating GPS accuracy circle:', e.message);
                 }
             }