diff --git a/lib/features/rides/ride_state_machine.dart b/lib/features/rides/ride_state_machine.dart
index ccd6b02..a57771c 100644
--- a/lib/features/rides/ride_state_machine.dart
+++ b/lib/features/rides/ride_state_machine.dart
@@ -12,7 +12,6 @@ import '../../services/audio_alert_service.dart';
 import '../records/records_service.dart';
 import '../garage/garage_providers.dart';
 import '../../services/field_test/field_test_logger.dart';
-import '../../services/github/github_sync_service.dart';
 
 enum RideState { idle, ready, riding, paused, finished }
 
@@ -377,14 +376,6 @@ class RideStateMachine extends StateNotifier<RideSession> {
       }
     } catch (_) {}
 
-    // Offline-first background synchronization to GitHub (if enabled)
-    final completedRideId = state.dbId;
-    if (completedRideId != null) {
-      try {
-        ref.read(githubSyncServiceProvider).queueRideForUpload(completedRideId);
-      } catch (_) {}
-    }
-
     state = state.copyWith(
       state: RideState.finished,
       healthStatus: RecordingHealthStatus.recordingComplete,
diff --git a/lib/main.dart b/lib/main.dart
index 93a1190..2b3e6d2 100644
--- a/lib/main.dart
+++ b/lib/main.dart
@@ -8,7 +8,7 @@ import 'firebase_options.dart';
 import 'core/theme/theme.dart';
 import 'core/router.dart';
 import 'features/records/records_service.dart';
-import 'services/sync/sync_providers.dart';
+import 'services/sync/sync_observer.dart';
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
@@ -47,9 +47,9 @@ class _MotorcycleDashAppState extends ConsumerState<MotorcycleDashApp> {
   @override
   void initState() {
     super.initState();
-    // Eagerly construct the sync manager so persisted outbox work is
-    // reconciled immediately at app startup, not only after visiting a sync UI.
-    ref.read(syncManagerProvider);
+    // Eagerly construct the sync observer so completed rides enter the durable
+    // outbox at startup scope, not only after visiting a sync UI.
+    ref.read(syncObserverProvider);
     _initDeepLinks();
   }
 
diff --git a/test/sync_test.dart b/test/sync_test.dart
index 37d5559..23b6049 100644
--- a/test/sync_test.dart
+++ b/test/sync_test.dart
@@ -1,3 +1,5 @@
+import 'dart:io';
+
 import 'package:flutter_test/flutter_test.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:drift/native.dart';
@@ -428,5 +430,102 @@ void main() {
       observer.onRideSessionChanged(prevSession, nextSession);
       expect(outbox.count, equals(1));
     });
+
+    test('Stage 2B: production startup instantiates the ride sync observer', () {
+      final mainSource = File('lib/main.dart').readAsStringSync();
+
+      expect(mainSource, contains("import 'services/sync/sync_observer.dart';"));
+      expect(mainSource, contains('ref.read(syncObserverProvider);'));
+    });
+
+    test('Stage 2B: completed ride transition enters durable firebase outbox', () async {
+      final outbox = SyncOutbox(prefs);
+      final provider = FakeSyncProvider(
+        providerId: 'firebase',
+        behavior: FakeSyncBehavior.authRequired,
+      );
+      final manager = SyncManager(
+        outbox,
+        initialProviders: [provider],
+        defaultProviderId: 'firebase',
+      );
+      final observer = SyncObserver(manager);
+      addTearDown(manager.dispose);
+
+      final previous = RideSession(
+        dbId: 901,
+        state: RideState.riding,
+        healthStatus: RecordingHealthStatus.recordingActive,
+      );
+      final completed = previous.copyWith(
+        state: RideState.finished,
+        healthStatus: RecordingHealthStatus.recordingComplete,
+      );
+
+      observer.onRideSessionChanged(previous, completed);
+      await Future<void>.delayed(Duration.zero);
+
+      final item = outbox.getItem(901, 'firebase');
+      expect(item, isNotNull);
+      expect(item?.localRideId, 901);
+      expect(item?.providerId, 'firebase');
+      expect(
+        prefs.getString(outbox.storageKey),
+        contains('"localRideId":901'),
+      );
+    });
+
+    test('Stage 2B: automatic completion does not invoke legacy queue path', () {
+      final rideStateMachineSource =
+          File('lib/features/rides/ride_state_machine.dart').readAsStringSync();
+      final legacyServiceSource =
+          File('lib/services/github/github_sync_service.dart').readAsStringSync();
+
+      expect(rideStateMachineSource, isNot(contains('queueRideForUpload')));
+      expect(
+        rideStateMachineSource,
+        isNot(contains('services/github/github_sync_service.dart')),
+      );
+      expect(legacyServiceSource, contains('queueRideForUpload'));
+      expect(legacyServiceSource, contains('uploadRideToGitHub'));
+    });
+
+    test('Stage 2B: duplicate completed emissions keep one active outbox item', () async {
+      final outbox = SyncOutbox(prefs);
+      final manager = SyncManager(
+        outbox,
+        initialProviders: [
+          FakeSyncProvider(
+            providerId: 'firebase',
+            behavior: FakeSyncBehavior.authRequired,
+          ),
+        ],
+        defaultProviderId: 'firebase',
+      );
+      final observer = SyncObserver(manager);
+      addTearDown(manager.dispose);
+
+      final riding = RideSession(
+        dbId: 902,
+        state: RideState.riding,
+        healthStatus: RecordingHealthStatus.recordingActive,
+      );
+      final finished = riding.copyWith(
+        state: RideState.finished,
+        healthStatus: RecordingHealthStatus.recordingComplete,
+      );
+
+      observer.onRideSessionChanged(riding, finished);
+      observer.onRideSessionChanged(riding, finished);
+      observer.onRideSessionChanged(finished, finished);
+      await Future<void>.delayed(Duration.zero);
+
+      expect(outbox.count, 1);
+      expect(
+        outbox.getAllItems().where((item) => item.localRideId == 902),
+        hasLength(1),
+      );
+      expect(outbox.getItem(902, 'firebase'), isNotNull);
+    });
   });
 }