Terminals, SSH sessions and port forwards stay open when the API restarts

Previously, an API release closed every open terminal and tunnel. The API now moves each one to the instance that serves next: the server sends {"type":"restart"}, then a resume token, and closes the WebSocket with code 1012 (Service Restart). The JavaScript and Python SDKs, the CLI and the console reconnect with the token immediately and continue from the exact byte where they stopped, with nothing lost or sent twice. Clients that speak the WebSocket protocol directly can follow the same steps; see Resuming terminals and tunnels after a restart.