WebSocket upgrade endpoint for ActionCable. Authentication uses the same credentials as HTTP: signed session cookie (browsers) or X-User-Token header (native clients). Unauthorized connections are rejected. Once connected, subscribe to channels by sending a subscribe command over the socket. Currently supported channel:

VarRequestChannel

Subscribe payload (sent by client over the socket): json { "command": "subscribe", "identifier": "{"channel":"VarRequestChannel","id":"<var_request_id>"}" }

The channel rejects the subscription if the VarRequest does not exist or is not owned by the authenticated user. Broadcasts received (one snapshot per state transition; if the VarRequest is already in a terminal state at subscribe time, the terminal snapshot is transmitted immediately): json {"status":"processing"} {"status":"completed","playback_url":"https://...modal.run?run_id=...&filename=overlay.mp4"} {"status":"failed","error":"DRS upstream failed: ..."}

Clients should unsubscribe once a terminal status (completed or failed) is received.