Completes the 7.4 remainder. Fedify's FetchError carries the failed
Response, so a 429 from a remote's outbox now reads Retry-After
(delta-seconds or HTTP-date per RFC 9110), arms a per-host backoff
(15 min default, capped at the 1 h poll interval), and pollRemoteActor
skips backing-off hosts before doing any DB or network work. State is
in-process like the pacing map — a restart costs at most one extra
request that re-arms the backoff. last_polled_at is deliberately not
stamped on a rate-limited poll so the hourly sweep retries.
Unit tests cover the header parser (incl. the V8 footgun where
Date.parse reads bare negative integers as years), default/cap
behavior, and window expiry; an integration test drives the full
FetchError path and asserts the second poll never touches the network.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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