Soft-delete an agent (tombstone) in the graph database.

Overview: The Python query service marks the agent instance deleted inside a transaction. List and search endpoints exclude tombstoned agents. Toolsets, tools, and knowledge linked to the agent are not removed by this call.

Permissions: Only the agent owner may delete (can_delete on the permission check).

Warning: All conversations with this agent will become inaccessible.

Gateway not-found behavior: Unknown agentKey, deleting an already-deleted agent, deleting another user's agent that is not shared with the caller, and GET /agents/{agentKey} after delete return HTTP 404 with an ErrorResponse body.

The route reads neither a query nor a body; anything sent is ignored.

{
  "message": "Agent deleted successfully",
  "deleted": {
    "agents": 1
  }
}