StripPathPrefix and the redirect from / and /browse still read
X-Forwarded-Prefix from any peer, after BaseURL and BasePathPrefix
were gated on --trusted-proxies. A client could make the server strip
a path prefix or add one to a redirect.
Gate both on the same trusted-proxy resolver. The resolver is now
stamped into the request before StripPathPrefix runs, and the check is
exported as ForwardedHeadersTrusted. The explorer has no
--trusted-proxies option and keeps its old behavior by trusting every
peer for this one header. The docs say that the prefix needs a trusted
proxy.
Assisted-by: Claude:claude-sonnet-5-5 go-test