There is no party capable to take responsibility on the other side of the handover protocol.

Yes, this is the thing - an agent is not a counter party. But it role plays one really well.

You would need the agent to be a processing step owned by someone responsible. But the intelligent part of an agent is what makes it viable as something more than a processing step. What to do with an intelligence that can't take responsibility? Not answering this question leads to cognitive debt.