32200c7b5f
internal/quiesce had no failure counter, no backoff and no breaker, and the driver is a plain 5-minute ticker — so a tier that was due and kept failing stopped and restarted every customer app stack every 5 minutes indefinitely. Live on demo-felhom 2026-07-27: three cycles in eleven minutes against an unreachable PBS tier; it ended only because PBS recovered. The breaker gates the QUIESCE, not the backup — the harm was the outage taken to attempt it, so backed-off tiers are dropped before any stack is stopped. Per target (a broken offsite tier must not suppress a healthy local one), 15m→30m→ 1h→2h→4h capped, reset on success, never permanent, never applied to TriggerNow, and stillRunning is not a failure. State is in-memory on purpose: forgetting a backoff costs one attempt; persisting one could outlive the fix. Part 3 invariant recorded on scheduledRunAllowed — a missing value means UNKNOWN, and only a positive 'never' may fire the safety valve. Fourth instance of the class (hub v0.12.0, v0.73.0, R-81, R-88). Part 2 (unknown != never) is NOT in this commit: the agent returns byte-identical responses for 'read errored' and 'never backed up', so the controller cannot tell them apart. That needs an agent wire change and is tracked separately.