The z.ai GLM coding endpoint intermittently accepts the chat request but never
sends response headers; undici's default 300s headersTimeout then hung the user
for five minutes before failing, and UND_ERR_HEADERS_TIMEOUT was not in the
RetryAgent's retried error set, so there was no recovery.
headersTimeout only bounds time-to-FIRST-headers (before any body) — it is NOT
the streaming budget, so lowering it does not truncate live SSE streams. Cap it
(env AI_HTTP_HEADERS_TIMEOUT_MS, default 60s) so a header stall fails fast, and
add UND_ERR_HEADERS_TIMEOUT to the retried error codes so the stalled request is
retried on a fresh connection (which usually responds in seconds). bodyTimeout
kept generous (env AI_HTTP_BODY_TIMEOUT_MS, default 300s) so slow streams with
sparse chunks survive. UND_ERR_BODY_TIMEOUT is deliberately NOT retried (mid-body,
partial SSE already delivered).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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