fix: retain last valid gps data

ref:

lib/providers/contacts_provider.dart

@@ -335,12 +335,9 @@ class ContactsProvider with ChangeNotifier {
       debugPrint('  ✅ Parsed new telemetry');
       debugPrint('  New telemetry timestamp: ${telemetry.timestamp}');
 
-      // Ignore placeholder GPS coordinates (0,0) so we don't overwrite a
-      // previously known/saved position with invalid telemetry data.
-      if (_isInvalidTelemetryGps(telemetry.gpsLocation)) {
-        debugPrint(
-          '  ⚠️ Ignoring invalid telemetry GPS coordinates: ${telemetry.gpsLocation}',
-        );
+      final incomingGps = telemetry.gpsLocation;
+      if (_isInvalidTelemetryGps(incomingGps)) {
+        // Always sanitize invalid placeholder GPS to null first.
         telemetry = ContactTelemetry(
           gpsLocation: null,
           batteryPercentage: telemetry.batteryPercentage,
@@ -353,6 +350,25 @@ class ContactsProvider with ChangeNotifier {
         );
       }
 
+      // Keep last valid GPS for router/chat/room contacts when current
+      // telemetry does not provide a valid GPS fix.
+      if (_shouldRetainLastValidGps(contact, telemetry.gpsLocation)) {
+        debugPrint(
+          '  ⚠️ Retaining last valid GPS. Incoming telemetry GPS is invalid/missing: $incomingGps',
+        );
+        final previousGps = _getValidGpsOrNull(contact.telemetry?.gpsLocation);
+        telemetry = ContactTelemetry(
+          gpsLocation: previousGps,
+          batteryPercentage: telemetry.batteryPercentage,
+          batteryMilliVolts: telemetry.batteryMilliVolts,
+          temperature: telemetry.temperature,
+          timestamp: telemetry.timestamp,
+          humidity: telemetry.humidity,
+          pressure: telemetry.pressure,
+          extraSensorData: telemetry.extraSensorData,
+        );
+      }
+
       // Update contact with new telemetry AND last seen time
       // lastAdvert is Unix timestamp in seconds
       final currentTimestamp = (DateTime.now().millisecondsSinceEpoch / 1000)
@@ -390,6 +406,29 @@ class ContactsProvider with ChangeNotifier {
     return lat.abs() < epsilon && lon.abs() < epsilon;
   }
 
+  LatLng? _getValidGpsOrNull(LatLng? location) {
+    if (location == null || _isInvalidTelemetryGps(location)) {
+      return null;
+    }
+    return location;
+  }
+
+  bool _shouldRetainLastValidGps(Contact contact, LatLng? incomingGps) {
+    final isSupportedType =
+        contact.isChat || contact.isRepeater || contact.isRoom;
+    if (!isSupportedType) {
+      return false;
+    }
+
+    final hasPreviousValidGps =
+        _getValidGpsOrNull(contact.telemetry?.gpsLocation) != null;
+    if (!hasPreviousValidGps) {
+      return false;
+    }
+
+    return incomingGps == null;
+  }
+
   /// Find contact by public key prefix (6 bytes)
   Contact? _findContactByPrefix(Uint8List prefix) {
     if (prefix.length < 6) return null;

test/providers/contacts_provider_test.dart

@@ -9,6 +9,29 @@ import 'package:shared_preferences/shared_preferences.dart';
 void main() {
   TestWidgetsFlutterBinding.ensureInitialized();
 
+  Uint8List createPublicKey(int seed) {
+    return Uint8List.fromList(List<int>.generate(32, (index) => seed + index));
+  }
+
+  Contact createContact({
+    required Uint8List key,
+    required ContactType type,
+    String? name,
+  }) {
+    return Contact(
+      publicKey: key,
+      type: type,
+      flags: 0,
+      outPathLen: 0,
+      outPath: Uint8List(64),
+      advName: name ?? 'Test Contact',
+      lastAdvert: DateTime.now().millisecondsSinceEpoch ~/ 1000,
+      advLat: (46.0569 * 1e6).toInt(),
+      advLon: (14.5058 * 1e6).toInt(),
+      lastMod: DateTime.now().millisecondsSinceEpoch ~/ 1000,
+    );
+  }
+
   group('ContactsProvider.updateTelemetry', () {
     late ContactsProvider provider;
     late Uint8List publicKey;
@@ -106,5 +129,70 @@ void main() {
       expect(updated.displayLocation!.latitude, closeTo(45.0001, 0.0001));
       expect(updated.displayLocation!.longitude, closeTo(13.9999, 0.0001));
     });
+
+    test(
+      'retains last valid gps for chat/repeater/room when telemetry gps is invalid or missing',
+      () {
+        final contactTypes = <ContactType>[
+          ContactType.chat,
+          ContactType.repeater,
+          ContactType.room,
+        ];
+
+        for (var i = 0; i < contactTypes.length; i++) {
+          final scopedProvider = ContactsProvider();
+          final scopedKey = createPublicKey(16 + i);
+          final contactType = contactTypes[i];
+          scopedProvider.addOrUpdateContact(
+            createContact(
+              key: scopedKey,
+              type: contactType,
+              name: 'Contact ${contactType.name}',
+            ),
+          );
+
+          final validGps = CayenneLppParser.createGpsData(
+            latitude: 45.1234,
+            longitude: 13.8765,
+          );
+          scopedProvider.updateTelemetry(scopedKey.sublist(0, 6), validGps);
+
+          // No GPS frame should keep previous valid GPS.
+          final batteryOnly = CayenneLppParser.createBatteryData(3.8);
+          scopedProvider.updateTelemetry(scopedKey.sublist(0, 6), batteryOnly);
+
+          var updated = scopedProvider.findContactByKey(scopedKey)!;
+          expect(updated.telemetry, isNotNull);
+          expect(updated.telemetry!.gpsLocation, isNotNull);
+          expect(
+            updated.telemetry!.gpsLocation!.latitude,
+            closeTo(45.1234, 0.0001),
+          );
+          expect(
+            updated.telemetry!.gpsLocation!.longitude,
+            closeTo(13.8765, 0.0001),
+          );
+
+          // Invalid 0,0 GPS frame should also keep previous valid GPS.
+          final invalidGps = CayenneLppParser.createGpsData(
+            latitude: 0.0,
+            longitude: 0.0,
+          );
+          scopedProvider.updateTelemetry(scopedKey.sublist(0, 6), invalidGps);
+
+          updated = scopedProvider.findContactByKey(scopedKey)!;
+          expect(updated.telemetry, isNotNull);
+          expect(updated.telemetry!.gpsLocation, isNotNull);
+          expect(
+            updated.telemetry!.gpsLocation!.latitude,
+            closeTo(45.1234, 0.0001),
+          );
+          expect(
+            updated.telemetry!.gpsLocation!.longitude,
+            closeTo(13.8765, 0.0001),
+          );
+        }
+      },
+    );
   });
 }