Codex/OpenAI upstream switched from a WebSocket pool to HTTP/2. The
outbound H2 transport set neither ReadIdleTimeout nor ResponseHeaderTimeout
(the OpenAI profile forces ResponseHeaderTimeout=0), so a pooled H2
connection silently killed by a proxy/NAT becomes a "dead connection":
both ends believe it is alive and a request assigned to it hangs until the
OS TCP retransmit timeout (minutes) before the first byte — observed as an
8m37s TTFT with an eventual 200. Occasional (only when a request lands on a
dead pooled conn) and across all groups (shared OpenAI transport); worse on
larger idle pools.
Explicitly configure http2 on the openai_h2 transport and enable active
PING health checks (ReadIdleTimeout=15s, PingTimeout=15s) so dead
connections are detected and evicted at the source, instead of relying on
ResponseHeaderTimeout as an after-the-fact backstop. Scoped to the
openai_h2 path only; Claude/Gemini (default) and h1 modes are untouched.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
