code: def add_ckpt_state(self, ckpt_id, ckpt_state):
      
      # first flush any buffered tuples
      self._flush_remaining()
      msg = ckptmgr_pb2.StoreInstanceStateCheckpoint()
      istate = ckptmgr_pb2.InstanceStateCheckpoint()
      istate.checkpoint_id = ckpt_id
      istate.state = ckpt_state
      msg.state.CopyFrom(istate)
      self._push_tuple_to_stream(msg)
docs: Add the checkpoint state message to be sent back the stmgr
  
      :param ckpt_id: The id of the checkpoint
      :ckpt_state: The checkpoint state