Gate finding C12 r3 #3 (2ab, toothless): nothing pinned
hermes.cron.store.writable / skipped_runs, and pinning them showed the
gauges never left the process. _OBSERVABLE_METRIC_NAMES is the list the OTLP
exporter observes, and a gauge missing from it is silently dropped, so
dashboards never saw an unwritable store. Register both, and add one test:
a degraded store exports writable=0 with skipped_runs=1, a cleared store
exports writable=1, and both names are registered. The test goes red with
de334a6b37's cron_health hunk reverted and also with this registration
reverted.
7d8ce0d898