The detector previously returned 1 on alerts, which made systemd
mark cis490-fleet-health.service as 'failed' every tick that found
a sick host. That's the wrong UX — a detector finding a fault is
working correctly, not crashing. The alert is the signal (via
WARNING log + alerts.jsonl); the unit's success state should mean
"the detector itself ran cleanly." Test added.
Caught while live-deploying on the Pi: the first run found
elliott-thinkpad fatal-only at 943×4xx + 1425×5xx and correctly
emitted the alert — but systemd showed the unit red, which would
have caused operators to chase the wrong tail.
Side note: the same first run also caught a real bug — pycache for
receiver.store on /opt/cis490 was stale after I deployed the new
app.py + store.py from main, causing 1464 × 500 responses. Cleared
the pycache and the index immediately resumed growing (4465 →
4515 in 30 seconds). The detector earned its keep on the very
first cycle.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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