The ops dashboard marked subscription-notifier DOWN ~2/3 of the time after the
notifier was gated to a single leader worker. It judged the daemon by whether
its thread was present on whichever worker answered /api/v2/metrics, but only
the leader runs it — so polls landing on the other two workers saw no thread and
reported DOWN for a perfectly healthy notifier. Per-worker thread checks can't
describe a single-leader daemon, and worse, they could no longer distinguish a
real crash from a normal non-leader.
Report it by liveness instead: the notifier stamps a heartbeat (timestamp +
expected interval) into the shared metrics store each loop iteration, including
once at startup so the dashboard shows it up immediately after a restart. Since
the beat lives in the shared SQLite store, any worker's metrics response carries
it, so the dashboard sees the notifier's health whichever worker it polls.
- metrics.py: both stores record/expose heartbeats (SQLite reuses the meta
table, so every worker's beats share one file); snapshot() converts each beat
to a server-computed age so readers needn't reconcile clock skew.
- notify.py: beat at loop start and every wake.
- dashboard.py: judge heartbeat daemons by freshness (up to 2 missed intervals
before DOWN, with beat age shown); neighbor-warmer keeps its per-worker thread
check, which is correct since every worker runs it.
- Tests: heartbeat store/snapshot shape + cross-worker sharing; dashboard
fresh/stale/missing rendering and the unchanged warmer check. 194 passed.
Co-authored-by: root <root@vmi3417050.contaboserver.net>
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