retryableStatus now treats 408 (Request Timeout) and 429 (Too Many
Requests) as retryable, matching the PHP-side equivalent. Retry loop
parses Retry-After from the response (seconds form OR HTTP-date),
clamps to 60s max, treats past dates as zero delay.
Tests cover: 408 retried, 429 retried, numeric Retry-After honoured,
past-date Retry-After produces zero sleep, long Retry-After capped.
Co-authored-by: Codex <noreply@openai.com>
Closes tasks.lthn.sh/view.php?id=996
2acf186925