Review follow-up on the #30223 salvage: the original changed the base
cooldown from 60s to 1800s, benching the primary for 30 minutes on the
FIRST 429 (30x regression in primary-restore latency) and breaking the
existing test_rate_limit_exhaustion_keeps_60s_cooldown contract.
Keep upstream's 60s base and escalate per consecutive rate-limit:
60s -> 2m -> 4m -> 8m -> ... capped at 4h. Counter still resets on
successful primary restore (cicae's mechanism, unchanged).
New tests: escalation doubling, 14400s cap, reset-on-restore.
Existing 60s contract test passes UNCHANGED. Mutation-checked:
escalation disabled -> 2 fail; reset disabled -> 1 fails.
