- warm_portraits: only 404/410 mark a headshot dead (measured: Plex answers a dead CDN file 404);
a refused token or a 5xx is Plex failing, ends the run after three in a row and marks nothing.
'failed' counts every failure, not only the current streak.
- is_portrait_url: plain path segments only — no dot or empty segment an HTTP client folds onto
one file; person_thumb_url uses the same predicate (27 852 stored headshots all pass).
- Tests: Plex refusing (401/403/429/5xx), failures between successes (portraits and bios), the kept
original served from cache, the audit_clear / demo_reset / discovery_purge rows' counts as data,
and the 0094 backfill on real rows.
