fix(monitor): improve duration calculation accuracy and robustness

- Use start_time for start event duration calculation to ensure consistency
- Add timestamp backfill for single message submission in task queue
- Ensure robust handling of missing timestamps

Author: [email protected]

src/memos/mem_scheduler/task_schedule_modules/dispatcher.py

@@ -186,7 +186,7 @@ def wrapped_handler(messages: list[ScheduleMessageItem]):
                             else None
                         ),
                         "event_duration_ms": start_delay_ms,
-                        "total_duration_ms": wait_sec * 1000,
+                        "total_duration_ms": self._calc_total_duration_ms(start_time, enq_ts),
                     },
                 )
 

src/memos/mem_scheduler/task_schedule_modules/task_queue.py

@@ -93,6 +93,8 @@ def submit_messages(self, messages: ScheduleMessageItem | list[ScheduleMessageIt
         if len(messages) < 1:
             logger.error("Submit empty")
         elif len(messages) == 1:
+            if getattr(messages[0], "timestamp", None) is None:
+                messages[0].timestamp = get_utc_now()
             enqueue_ts = to_iso(getattr(messages[0], "timestamp", None))
             emit_monitor_event(
                 "enqueue",