gps manipulations tailored to sim7600h hat

pi/ui/lib/app_root.dart

@@ -41,6 +41,7 @@ class _AppRootState extends State<AppRoot> {
     // Show all items from the start so the row doesn't jump around
     _updateStatus('Config', '...');
     _updateStatus('UART', '...');
+    _updateStatus('GPS', '...');
     _updateStatus('Navigator', '...');
 
     // Config must load first (everything else depends on it)
@@ -48,11 +49,13 @@ class _AppRootState extends State<AppRoot> {
     await ConfigService.instance.load();
     _updateStatus('Config', 'Ready');
 
-    // UART health check and navigator image preload run truly in parallel
+    // UART, GPS, and navigator image preload run truly in parallel
     _updateStatus('UART', 'Connecting');
+    _updateStatus('GPS', 'Waiting');
     _updateStatus('Navigator', 'Loading');
     await Future.wait([
       _waitForUart(),
+      _waitForGps(),
       _preloadNavigatorImages(),
     ]);
 
@@ -100,6 +103,39 @@ class _AppRootState extends State<AppRoot> {
     _updateStatus('UART', 'Timeout');
   }
 
+  /// Poll backend health endpoint until GPS has a fix, or bail after 7.5s
+  Future<void> _waitForGps() async {
+    final backendUrl = ConfigService.instance.backendUrl;
+    const bailOut = Duration(milliseconds: 7500);
+    const retryDelay = Duration(seconds: 1);
+    final deadline = DateTime.now().add(bailOut);
+
+    _updateStatus('GPS', 'Acquiring');
+
+    while (DateTime.now().isBefore(deadline)) {
+      try {
+        final response = await http
+            .get(Uri.parse('$backendUrl/health'))
+            .timeout(const Duration(seconds: 2));
+
+        if (response.statusCode == 200) {
+          final data = jsonDecode(response.body) as Map<String, dynamic>;
+          if (data['gps_state'] == 'fix') {
+            _updateStatus('GPS', 'Ready');
+            return;
+          }
+        }
+      } catch (e) {
+        // Backend not reachable yet - keep trying
+      }
+
+      await Future.delayed(retryDelay);
+    }
+
+    // Bail out - dashboard will show live GPS state when it arrives
+    _updateStatus('GPS', 'Timeout');
+  }
+
   /// Preload navigator images into Flutter's image cache
   ///
   /// Scans for all PNGs in the navigator folder and precaches them.