Soft-delete an agent owned by the caller’s organization
deleted_at on the record. The agent and its
versions remain in the database so existing sessions and message history are
preserved, but the agent is hidden from List Agents
and new work against it is rejected.
The call is idempotent — calling it again on an already-deleted agent returns
the same deleted_at timestamp set by the first call.
After deletion, subsequent calls to
Publish Version and
Create Session for this agent_id
return 404 Not Found.
null if none was active.