Per-key WebSocket connection process for the Responses Provider.
The process owns connection-local optimization state: socket, latest
previous_response_id, prompt input prefix, keepalive timers, and temporary
degraded/backoff state. It does not own Session History. If continuation state is
missing or invalid, the caller can still replay from Pixir's Log over HTTP/SSE or a
fresh WebSocket. The default idle window is deliberately agent-scale so ordinary
pauses between Turns do not erase same-socket continuation evidence.
Summary
Functions
Returns a specification to start this module under a supervisor.