Reports whether close has run — a LIFECYCLE-only read that reaches no adapter and performs no I/O (M90b).

isHealthy() answers two questions at once: the service's own lifecycle AND the adapter's readiness. The database health indicator gates on lifecycle uncached — a closed database must read down immediately, never from an outcome cached before close — and bounds the adapter question inside its cached probe. Reading isHealthy() for the gate therefore called the adapter on the ONE path that is deliberately outside that bound, and made a poll cost two readiness reads instead of one. This is the gate.