The WebSocket surface.

Events are versioned (v1.write, v1.search) so a change that would break a client can arrive as v2 with this one still answering. Every call goes through the AgentDb facade, and every one answers -- a call that cannot be served comes back as an error the client can act on, and the connection stays usable afterwards.

A call deferred only because a model is still loading is reported distinctly from a call that failed, so a client retries the first rather than concluding the capability is gone.