A flat 30-minute quarantine retries a weekly subscription limit about
336 times before the window resets. BackendQuarantine now doubles the
cooldown on each consecutive exhaustion of the same credential (no
more than one base cooldown after the previous quarantine's deadline),
capped at 12x the base cooldown (~6h at the 1800s default), and resets
back to the base cooldown once a base-cooldown's worth of quiet has
passed with no further exhaustion.
The flat two-argument constructor is unchanged (equivalent to
multiplier 1.0 / ceiling == base), so all ~20 existing call sites keep
their current shape and behaviour. Production wiring (Fleetd.main)
switches to the new BackendQuarantine.withEscalation factory.
This only touches the exhaustion path (BackendQuarantine's one
production caller is Fleetd.exhaustionSink, fired on BACKEND_EXHAUSTED
alone) and never the separate, unescalated cooling-off mechanism
(BackendOutagePolicy, fixed 60s) that guards against a transient
backend-error storm.
Dai Ha
5a467e1f8b