New /admin/health rolls up signals already collected — disk/memory sensors,
dead-job + missing-cover backlogs, 24h crawl/analysis failure rates, metadata
cron freshness, and the live crawler session/browser flags — into a flat
checks list (ok/warn/critical) with an overall status and remediation links.
The overview gains a compact Health summary banner linking in.
GET /v1/admin/health evaluates the checks (DB sub-queries run concurrently via
try_join; all hit existing indexes). PUT /v1/admin/health/thresholds persists
the thresholds to app_settings (merged over compiled defaults, forward-compat
via serde(default)), validates ranges (400 on bad input), and audit-logs the
change in one transaction. New repo::crawler::last_metadata_tick_at getter and
a lightweight system::memory_percent_used (no CPU settle delay).
Pure status helpers (over_limit for gauges, exceeds for backlog counts so a
0-limit doesn't false-alarm at 0) are unit-tested; endpoint tests cover shape,
gating, persistence+audit, and validation.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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