Refines the #144 timeout decision with measured data. A 30-min probe of paced
single z.ai requests: 22/22 succeeded, TTFB 1.6–9.9s, zero timeouts/429s, no
multi-minute hang. So z.ai answers fast when NOT bursted; the reported
"hangs tens of minutes" is the burst path (20-step agent + stacked retries),
addressed by the per-host concurrency gate + 429 backoff.
Therefore headersTimeout/bodyTimeout default to 120s (env-overridable; 0 to
disable) rather than 0/infinite: 120s is ~12× the worst observed paced TTFB, so
it tolerates real slow turns but cuts a genuinely-stuck request with a clear
error instead of hanging for minutes (curl-style "wait forever" was too loose;
#141's 60s was too tight). Sanitizer now falls back to the default on a bad env
value; an explicit env 0 still disables.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
e5effa13e1