- Rebuild a bare-path plain-HTTP request's URL from Host, answer 400
"no host in request" when there is none, and refuse with 508 a rebuilt
request that is routed back into the proxy, which would otherwise loop
without end.
- Drop Host when forwarding to an HTTP/2 upstream. Google's servers reset
every stream that carries Host alongside :authority.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>