docs: def send(self, frame):
          """
          Handle the SEND command: Delivers a message to a queue or topic (default).
          """
          dest = frame.headers.get('destination')
          if not dest:
              raise ProtocolError('Missing destination for SEND command.')
  
          if dest.startswith('/queue/'):
              self.engine.queue_manager.send(frame)
          else:
              self.engine.topic_manager.send(frame)