fix duplicate message

app/sheets.py

@@ -191,7 +191,7 @@ class SheetsClient:
                     vehicle,
                     action,
                     purpose,
-                    json.dumps([timestamp]),
+                    json.dumps(timestamp),
                     str(is_done).lower()
                 ]
 
@@ -221,11 +221,14 @@ class SheetsClient:
                     'originalvehicle': vehicle,
                     'originalaction': action,
                     'originalpurpose': purpose,
-                    'timestamp': [timestamp],
+                    'timestamp': timestamp,
                     'isdone': is_done
                 }
             else:
                 # Update existing conversation
+                if not values:
+                    logger.error("No data in sheet, cannot update conversation.")
+                    return None
                 header = values[0]
                 data_rows = values[1:]
                 logger.info(f"[DEBUG] Gsheet data_rows {data_rows}")