starting the session fails silently when websockets are blocked

[binford2k]

If a firewall or DPI between the user and the server alters the websocket packets (e.g., degrading them to standard HTTP) then the terminal just silently fails to load. In the js console you see unexpected 200 statuses. It's expecting a 101 Switching Protocols instead.

This indicates that a websocket connection was attempted, but the packets weren't valid, so the server responds with the standard HTML page. The WebSocket() call in js doesn't know how to respond to that and just fails.

Instead, we should detect that, or catch errors, and display an informative error message.