Fix timezone handling in cluster client uptime calculation

- Store connected_at as UTC ISO string with Z suffix
- Handle datetime objects from database as UTC timestamps
- Ensure uptime calculation uses correct UTC times regardless of server timezone

vidai/database.py

@@ -1656,14 +1656,15 @@ def save_cluster_client(client_id: str, token: str, hostname: str, ip_address: s
     if connected_at is None:
         connected_at = time.time()
 
-    # Store as Unix timestamp (float) to avoid timezone issues
-    connected_at_value = connected_at
+    # Store as ISO UTC string with Z suffix to avoid timezone issues
+    from datetime import datetime
+    connected_at_str = datetime.utcfromtimestamp(connected_at).isoformat() + 'Z'
 
     config = get_db_config()
     if config['type'] == 'mysql':
         cursor.execute('''
             INSERT INTO cluster_clients (client_id, token, hostname, ip_address, weight, gpu_info, available_backends, connected, connected_at, last_seen)
-            VALUES (?, ?, ?, ?, ?, ?, ?, 1, FROM_UNIXTIME(?), CURRENT_TIMESTAMP)
+            VALUES (?, ?, ?, ?, ?, ?, ?, 1, ?, CURRENT_TIMESTAMP)
             ON DUPLICATE KEY UPDATE
                 hostname = VALUES(hostname),
                 ip_address = VALUES(ip_address),
@@ -1671,16 +1672,16 @@ def save_cluster_client(client_id: str, token: str, hostname: str, ip_address: s
                 gpu_info = VALUES(gpu_info),
                 available_backends = VALUES(available_backends),
                 connected = 1,
-                connected_at = FROM_UNIXTIME(?),
+                connected_at = VALUES(connected_at),
                 last_seen = CURRENT_TIMESTAMP
-        ''', (client_id, token, hostname, ip_address, weight, gpu_info_json, available_backends_json, connected_at_value, connected_at_value))
+        ''', (client_id, token, hostname, ip_address, weight, gpu_info_json, available_backends_json, connected_at_str))
     else:
         # For SQLite
         cursor.execute('''
             INSERT OR REPLACE INTO cluster_clients
             (client_id, token, hostname, ip_address, weight, gpu_info, available_backends, connected, connected_at, last_seen)
-            VALUES (?, ?, ?, ?, ?, ?, ?, 1, datetime(?, 'unixepoch'), CURRENT_TIMESTAMP)
-        ''', (client_id, token, hostname, ip_address, weight, gpu_info_json, available_backends_json, connected_at_value))
+            VALUES (?, ?, ?, ?, ?, ?, ?, 1, ?, CURRENT_TIMESTAMP)
+        ''', (client_id, token, hostname, ip_address, weight, gpu_info_json, available_backends_json, connected_at_str))
 
     conn.commit()
     success = cursor.rowcount > 0

vidai/web.py

@@ -444,11 +444,22 @@ def api_cluster_nodes():
             connected_at = client.get('connected_at')
             if connected_at:
                 if isinstance(connected_at, str):
-                    # Parse timestamp string
+                    # Parse ISO UTC string (with Z suffix)
                     import datetime
+                    if connected_at.endswith('Z'):
+                        connected_at = datetime.datetime.fromisoformat(connected_at[:-1] + '+00:00').timestamp()
+                    else:
+                        # Fallback for other formats
                         connected_at = datetime.datetime.fromisoformat(connected_at.replace('Z', '+00:00')).timestamp()
                 elif hasattr(connected_at, 'timestamp'):
-                    # datetime object
+                    # datetime object - assume it's in UTC (make it timezone aware)
+                    import datetime
+                    if connected_at.tzinfo is None:
+                        # Naive datetime, assume it's UTC
+                        utc_dt = connected_at.replace(tzinfo=datetime.timezone.utc)
+                        connected_at = utc_dt.timestamp()
+                    else:
+                        # Already timezone aware
                         connected_at = connected_at.timestamp()
                 # If it's already a float/int timestamp, use it directly
                 uptime_seconds = current_time - connected_at