Add the shared vocabulary for the polite-fetch subsystem (fetch-policy.md, interfaces.md §3a):
- FeedStatus::Dead, the terminal permanent-gone state (+ is_dead()).
- Feed politeness fields: enabled, etag, last_modified, advertised_min, freshness_until, retry_after_until.
- Seam types: ConditionalCtx, HttpMeta, FetchOutcome, RefreshTrigger, FeedSchedule.
- Pure feed_eligible(schedule, now, trigger): the max(...) politeness floor; Dead never eligible; advisory floors self-heal; unparseable now fails closed.
- Pure backoff_delay(attempt, base, cap, jitter01): full jitter via a caller-supplied fraction, keeping domain rand-free.
- Config: retry_count default 5->3, new retry_base_secs/retry_cap_secs.
chrono added (no clock feature) for the pure date arithmetic. +10 unit tests.
Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com