Octokit has no throttling plugin, so under a flood of PR-status calls a
primary/secondary rate limit just surfaced as repeated 403s that the cache
masked. Add a shared rate-limit gate: PR-status sub-calls note 403/429
responses, and the route short-circuits to cached/stale data during the
cooldown instead of issuing more doomed requests. Transient failures
(rate limit or the overall timeout) no longer log as hard errors.