Std.Http server answers HTTP/1.0 requests with an HTTP/1.0 status-line #16332

Description

RFC 9110 §6.2: "A server SHOULD send a response version equal to the highest version to which the
server is conformant that has a major version less than or equal to the one received in the
request." Std.Http's H1 machine writes the request's version instead (writeHead, version := machine.reader.messageHead.version), so a 1.0 request gets HTTP/1.0 200 OK.

#eval statusLine "GET / HTTP/1.1\r\nHost: a\r\n\r\n"   -- "HTTP/1.1 200 OK"
#eval statusLine "GET / HTTP/1.0\r\n\r\n"              -- "HTTP/1.0 200 OK"

(Repro.lean attached: feeds the bytes to Protocol.H1.Machine .receiving and answers 200.)

Expected

HTTP/1.1 200 OK in both cases, with the 1.0-specific framing (no chunked, Connection: close
unless keep-alive was asked) unchanged.

Versions

v4.35.0, nightly-2026-11-06, master 2026-11-07 (encodeServerHead).

Found while auditing RFC 9110/9112 conformance of Std.Http (Lean v4.35.0, re-checked against master 2026-11-07). Standalone repro available on request.

This report was prepared and written with AI assistance (Claude).