fix(#672): end a silent contact stream after 30 s on its own

The 30 s staleness rule only ran when a later getContacts call checked it.
If the radio drops END (firmware #1283 can refuse it like any frame) and
nothing else asks for contacts, the request stayed in flight: the loading
state stuck and a queued refresh never ran.

A watchdog now fires at the stale mark, re-arms if frames are still
arriving, and otherwise ends the request and runs the queued one. It never
prunes: an unfinished stream is not a complete sync.

Found by the pre-PR Gemini review.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/connector/meshcore_connector.dart

@@ -454,6 +454,7 @@ class MeshCoreConnector extends ChangeNotifier {
   bool _contactStreamStarted = false;
   DateTime _contactRequestLastActivity = DateTime.fromMillisecondsSinceEpoch(0);
   ({int? since, bool preserveExisting})? _queuedContactRequest;
+  Timer? _contactRequestWatchdog;
 
   @visibleForTesting
   DateTime Function() contactSyncClock = DateTime.now;
@@ -3145,6 +3146,8 @@ class MeshCoreConnector extends ChangeNotifier {
     _contactSyncDeliveredKeys.clear();
     _contactSyncRetryUsed = false;
     _contactSyncDecisionPending = false;
+    _contactRequestWatchdog?.cancel();
+    _contactRequestWatchdog = null;
     _contactRequestInFlight = false;
     _contactStreamStarted = false;
     _queuedContactRequest = null;
@@ -3724,6 +3727,7 @@ class MeshCoreConnector extends ChangeNotifier {
     _contactRequestInFlight = true;
     _contactStreamStarted = false;
     _contactRequestLastActivity = contactSyncClock();
+    _armContactRequestWatchdog();
 
     _isLoadingContacts = true;
     _contactSyncTotal = null;
@@ -3765,12 +3769,47 @@ class MeshCoreConnector extends ChangeNotifier {
   }
 
   void _endContactRequest() {
+    _contactRequestWatchdog?.cancel();
+    _contactRequestWatchdog = null;
     _contactRequestInFlight = false;
     _contactStreamStarted = false;
     _isLoadingContacts = false;
     _contactSyncIsFull = false;
   }
 
+  void _armContactRequestWatchdog() {
+    _contactRequestWatchdog?.cancel();
+    final idle = contactSyncClock().difference(_contactRequestLastActivity);
+    final wait = contactRequestStaleAfter - idle;
+    _contactRequestWatchdog = Timer(
+      wait.isNegative ? Duration.zero : wait,
+      checkStaleContactRequest,
+    );
+  }
+
+  /// Ends a request whose stream went silent for [contactRequestStaleAfter]
+  /// without END, so it cannot hold the queue or the loading state until some
+  /// later refresh happens to run. Nothing is pruned: an unfinished stream is
+  /// never a complete sync.
+  @visibleForTesting
+  void checkStaleContactRequest() {
+    if (!_contactRequestInFlight) return;
+    final idle = contactSyncClock().difference(_contactRequestLastActivity);
+    if (idle < contactRequestStaleAfter) {
+      _armContactRequestWatchdog();
+      return;
+    }
+    _appDebugLogService?.warn(
+      'Contact request had no reply for ${idle.inSeconds}s; ending it, saved '
+      'contacts kept',
+      tag: 'ContactSync',
+    );
+    _endContactRequest();
+    _hasLoadedContacts = true;
+    notifyListeners();
+    _runQueuedContactRequest();
+  }
+
   void _runQueuedContactRequest() {
     final queued = _queuedContactRequest;
     if (queued == null || _contactRequestInFlight) return;
@@ -8802,6 +8841,7 @@ class MeshCoreConnector extends ChangeNotifier {
     _gpsLocationPollTimer?.cancel();
     _radioStatsPollTimer?.cancel();
     _channelsChangedDebounce?.cancel();
+    _contactRequestWatchdog?.cancel();
     radioStatsNotifier.dispose();
     _receivedFramesController.close();
     _usbManager.dispose();

test/connector/contact_sync_test.dart

@@ -296,6 +296,26 @@ void main() {
       expect(contactRequests(), 1);
     });
 
+    test('a stream that never ends is ended at 30 s without pruning', () async {
+      seedSaved();
+      await connector.getContacts();
+      connector.handleFrameForTest(_start(3));
+      connector.handleFrameForTest(_contactFrame(0x11, 'Alpha'));
+      await connector.getContacts(since: 5, preserveExisting: true);
+
+      now = now.add(const Duration(seconds: 29));
+      connector.checkStaleContactRequest();
+      expect(connector.isLoadingContacts, isTrue, reason: 'live at 29 s');
+
+      now = now.add(const Duration(seconds: 2));
+      connector.checkStaleContactRequest();
+      await Future<void>.delayed(Duration.zero);
+
+      expect(names(), {'Alpha', 'Bravo', 'Charlie'});
+      expect(contactRequests(), 2, reason: 'the queued request ran');
+      expect(sent.last.length, 5, reason: 'the queued incremental request');
+    });
+
     test('a failed send does not leave refreshes blocked', () async {
       connector.sendFrameOverrideForTest = (_) => throw Exception('usb gone');
       await expectLater(connector.getContacts(), throwsException);