docs: def process_event(self, event_id):
      """Process event in Celery."""
      with db.session.begin_nested():
          event = Event.query.get(event_id)
          event._celery_task = self  # internal binding to a Celery task
          event.receiver.run(event)  # call run directly to avoid circular calls
          flag_modified(event, 'response')
          flag_modified(event, 'response_headers')
          db.session.add(event)
      db.session.commit()