QuotaCell::observe_at is the one decision for both sensors: a reading older
than the held one is dropped, and a rejection stands against a reading that
only reports utilization (status polled) until its window resets or a reading
that carries its own verdict replaces it. The poll stamps its answer with the
moment it asked. Also: Retry-After in HTTP-date form is honoured; a refused
token is not sent again until it reads differently (the poll thread no longer
exits); the client's timeout is a parameter so a silent endpoint is tested;
tests pin redirects(0), the two-window mapping, the slow-server race, and the
late poll against a rejection.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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