c7ccb5798c
Dual-channel opening: consecutive failures (CHS-compatible, no streak bump) plus windowed failure rate (two 30s buckets, min_calls guard). 429s bypass both channels as backpressure, and a probe hitting 429 releases instead of holding the lease. Open duration doubles per rate/probe reopen up to max_cooldown_s, decaying after stable CLOSED. record_success gains count_attempt so bad-result successes stay out of the window.