fix: ignore zeroed telemetry gps coords

Fixes #4\nRefs #5\n\nref:

lib/providers/contacts_provider.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/foundation.dart';
+import 'package:latlong2/latlong.dart';
 import '../models/contact.dart';
 import '../services/cayenne_lpp_parser.dart';
 import '../services/contact_storage_service.dart';
@@ -330,10 +331,28 @@ class ContactsProvider with ChangeNotifier {
 
     try {
       // Parse Cayenne LPP data
-      final telemetry = CayenneLppParser.parse(lppData);
+      var telemetry = CayenneLppParser.parse(lppData);
       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}',
+        );
+        telemetry = ContactTelemetry(
+          gpsLocation: null,
+          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)
@@ -359,6 +378,18 @@ class ContactsProvider with ChangeNotifier {
     }
   }
 
+  bool _isInvalidTelemetryGps(LatLng? location) {
+    if (location == null) return false;
+    final lat = location.latitude;
+    final lon = location.longitude;
+
+    if (!lat.isFinite || !lon.isFinite) return true;
+
+    // Many devices report "0000" placeholder GPS as (0.0, 0.0).
+    const epsilon = 1e-7;
+    return lat.abs() < epsilon && lon.abs() < epsilon;
+  }
+
   /// Find contact by public key prefix (6 bytes)
   Contact? _findContactByPrefix(Uint8List prefix) {
     if (prefix.length < 6) return null;

test/providers/contacts_provider_test.dart

@@ -0,0 +1,110 @@
+import 'dart:typed_data';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:meshcore_sar_app/models/contact.dart';
+import 'package:meshcore_sar_app/providers/contacts_provider.dart';
+import 'package:meshcore_sar_app/services/cayenne_lpp_parser.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  group('ContactsProvider.updateTelemetry', () {
+    late ContactsProvider provider;
+    late Uint8List publicKey;
+
+    setUp(() {
+      SharedPreferences.setMockInitialValues({});
+      provider = ContactsProvider();
+      publicKey = Uint8List.fromList([
+        0xAA,
+        0xBB,
+        0xCC,
+        0xDD,
+        0xEE,
+        0xFF,
+        0x01,
+        0x02,
+        0x03,
+        0x04,
+        0x05,
+        0x06,
+        0x07,
+        0x08,
+        0x09,
+        0x0A,
+        0x0B,
+        0x0C,
+        0x0D,
+        0x0E,
+        0x0F,
+        0x10,
+        0x11,
+        0x12,
+        0x13,
+        0x14,
+        0x15,
+        0x16,
+        0x17,
+        0x18,
+        0x19,
+        0x1A,
+      ]);
+
+      provider.addOrUpdateContact(
+        Contact(
+          publicKey: publicKey,
+          type: ContactType.chat,
+          flags: 0,
+          outPathLen: 0,
+          outPath: Uint8List(64),
+          advName: 'Test Contact',
+          lastAdvert: DateTime.now().millisecondsSinceEpoch ~/ 1000,
+          advLat: (46.0569 * 1e6).toInt(),
+          advLon: (14.5058 * 1e6).toInt(),
+          lastMod: DateTime.now().millisecondsSinceEpoch ~/ 1000,
+        ),
+      );
+    });
+
+    test('ignores telemetry GPS at 0,0 and keeps advert location', () {
+      final lppData = CayenneLppParser.createGpsData(
+        latitude: 0.0,
+        longitude: 0.0,
+      );
+
+      provider.updateTelemetry(publicKey.sublist(0, 6), lppData);
+      final updated = provider.findContactByKey(publicKey)!;
+
+      expect(updated.telemetry, isNotNull);
+      expect(updated.telemetry!.gpsLocation, isNull);
+      expect(updated.displayLocation, isNotNull);
+      expect(updated.displayLocation!.latitude, closeTo(46.0569, 0.000001));
+      expect(updated.displayLocation!.longitude, closeTo(14.5058, 0.000001));
+    });
+
+    test('keeps valid telemetry GPS and uses it for display location', () {
+      final lppData = CayenneLppParser.createGpsData(
+        latitude: 45.0001,
+        longitude: 13.9999,
+      );
+
+      provider.updateTelemetry(publicKey.sublist(0, 6), lppData);
+      final updated = provider.findContactByKey(publicKey)!;
+
+      expect(updated.telemetry, isNotNull);
+      expect(updated.telemetry!.gpsLocation, isNotNull);
+      expect(
+        updated.telemetry!.gpsLocation!.latitude,
+        closeTo(45.0001, 0.0001),
+      );
+      expect(
+        updated.telemetry!.gpsLocation!.longitude,
+        closeTo(13.9999, 0.0001),
+      );
+      expect(updated.displayLocation, isNotNull);
+      expect(updated.displayLocation!.latitude, closeTo(45.0001, 0.0001));
+      expect(updated.displayLocation!.longitude, closeTo(13.9999, 0.0001));
+    });
+  });
+}