📝 Bug Description

The syncOfflineQueue function in src/services/syncQueue.ts silently skips every queued session when currentUserId is null (user not logged in), returning { synced: 0, failed: 0 } as if everything completed successfully. The caller assumes sync was successful with nothing to sync, but the queue still contains pending sessions that will never be delivered.

Bug location — src/services/syncQueue.ts:52-59:

export async function syncOfflineQueue(): Promise<SyncResult> {
  const currentUserId = getAuth().currentUser?.uid;  // null if not logged in
  const queue = getQueue();
  let synced = 0;
  let failed = 0;

  for (const session of queue) {
    if (!currentUserId || session.userId !== currentUserId) {
      continue;  // ← silently skips ALL sessions when currentUserId is null
    }
    // ... upload logic never reached ...
  }
  return { synced, failed };  // { synced: 0, failed: 0 }
}

When currentUserId is null:

• First condition !currentUserId is true for EVERY session
• Every session is skipped via continue
• Function returns { synced: 0, failed: 0 } — caller assumes success
• Queue data stays in localStorage forever

🔄 Steps To Reproduce

1. Record workout sessions while offline (or while not authenticated)
2. Data gets pushed to the offline queue in localStorage
3. User does NOT log in / auth session expires
4. syncOfflineQueue() is called (e.g., via auto-sync timer)
5. currentUserId is null
6. All sessions skipped silently
7. Returns { synced: 0, failed: 0 }
8. Caller assumes nothing to sync — queue never retried or cleared
9. Offline data lost permanently

✅ Expected Behavior

• When currentUserId is null, either:
  • Wait for authentication before attempting sync
  • Or return an error/status indicating auth is required
  • Or at minimum, log a warning that sessions are pending authentication

❌ Actual Behavior

• Returns success with zero counts — indistinguishable from "nothing to sync"
• Offline data permanently orphaned
• No warning to user or developer

🌐 Browser

Chrome

💻 Operating System

All

📦 Node.js Version

v20.x

📌 Additional Context

Impact: Offline workout data is silently lost when user is not authenticated during sync. User has no indication that data was not uploaded.
Level: 2 (Intermediate) — add auth-state check and appropriate handling