Send a context clear marker to an agent's conversation with a user.

The agent treats only messages after the latest marker as conversation history; everything earlier stays stored and reachable through its conversation tools.

Participants see a divider.

The cut applies to the conversation regardless of who sent the marker.

Two modes, consistent with the message commands:

Owner mode: both names identify the conversation; the marker is

sent as you (owner guest-send), using your login.

mutiro agent conversation clear myagent_AB12 someuser

Agent-key mode: the agent is implied by the key; the marker is

sent as the agent (e.g.

task-boundary clears from scripts).

mutiro agent conversation clear someuser --api-key

Useful headlessly for eval hygiene: clear the eval conversation before a suite run so earlier probes cannot contaminate the behavior being measured.

mutiro agent conversation clear [agent] [username] [flags]