The sandbox proxy now provides more specific error messages for connection failures:
"CONNECT handshake timed out"— timeout during proxy CONNECT"Proxy closed during CONNECT handshake"— premature close"Proxy refused CONNECT: ..."— non-2xx response from proxy"CONNECT response header too large"— headers exceeding 16KB"Denying malformed host: ..."/"Rejecting malformed SOCKS host: ..."— input validation"Invalid destination host for CONNECT"/"Invalid destination port"— bad target validation"Invalid parent proxy URL, ignoring: ..."— misconfigured parent proxy URL"unsupported scheme or empty host"— bad proxy URL scheme
Evidence
CONNECT tunnel error handling (search for "CONNECT handshake timed out" and "Proxy refused CONNECT")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.