Prepare secure config and reliable workout sync

mobile/lib/services/sync_service.dart

@@ -31,13 +31,12 @@ class SyncService extends GetxService {
   static const String _apiKeyKey = 'api_key';
   static const String _apiSecretKey = 'api_secret';
 
-  @override
-  Future<void> onInit() async {
-    super.onInit();
+  Future<SyncService> init() async {
     await _checkConnectivity();
     _startConnectivityMonitor();
     _startPeriodicSync();
     await _updatePendingCount();
+    return this;
   }
 
   // ─── Connectivity Monitoring ──────────────────────────────────
@@ -107,7 +106,7 @@ class SyncService extends GetxService {
   /// Queue a workout for sync
   Future<void> queueWorkout(Workout workout) async {
     final payload = jsonEncode(workout.toApiPayload());
-    await _db.enqueueSync(workout.id, payload);
+    await _db.saveCompletedWorkout(workout, payload);
     await _updatePendingCount();
 
     // Try immediate sync if online
@@ -116,6 +115,14 @@ class SyncService extends GetxService {
     }
   }
 
+  Future<void> retryWorkout(String workoutId) async {
+    await _db.retryFailedSync(workoutId);
+    await _updatePendingCount();
+    if (_isOnline.value && !_isSyncing.value) {
+      await syncPendingWorkouts();
+    }
+  }
+
   /// Process all pending sync items
   Future<void> syncPendingWorkouts() async {
     if (_isSyncing.value) return;
@@ -135,6 +142,7 @@ class SyncService extends GetxService {
       debugPrint('[SYNC] Processing ${pendingItems.length} pending items');
 
       for (final item in pendingItems) {
+        if (!_isRetryDue(item)) continue;
         await _syncSingleItem(
           id: item['id'] as int,
           workoutId: item['workout_id'] as String,
@@ -177,7 +185,7 @@ class SyncService extends GetxService {
           )
           .timeout(const Duration(seconds: 30));
 
-      if (response.statusCode == 201) {
+      if (response.statusCode == 200 || response.statusCode == 201) {
         await _db.updateSyncQueueItem(id, 'sent');
         await _db.updateSyncStatus(
           workoutId,
@@ -200,8 +208,20 @@ class SyncService extends GetxService {
   }
 
   Future<void> _updatePendingCount() async {
-    final items = await _db.getPendingSyncs();
-    _pendingCount.value = items.length;
+    _pendingCount.value = await _db.getPendingSyncCount();
+  }
+
+  bool _isRetryDue(Map<String, dynamic> item) {
+    if (item['status'] != 'failed') return true;
+    final lastAttempt = item['last_attempt'] as String?;
+    if (lastAttempt == null) return true;
+
+    final retryCount = item['retry_count'] as int? ?? 0;
+    final delaySeconds = (30 * (1 << retryCount)).clamp(30, 3600);
+    final attemptedAt = DateTime.tryParse(lastAttempt);
+    if (attemptedAt == null) return true;
+    return DateTime.now().toUtc().difference(attemptedAt.toUtc()).inSeconds >=
+        delaySeconds;
   }
 
   @override