raise on misdirected websocket handshake
Responding "HTTP/1.1 101 Switching Protocols" to a HEAD or POST request is unlikely intended.
Spec says **"MUST stop"** for non-GET requests: https://datatracker.ietf.org/doc/html/rfc6455#section-4.2.1
There is precedent for being strict about 1xx informational responses that might confuse a proxy, see expect-100 processing.