Follow-up to the album-art resolution fix. That change upgraded MusicBrainz
Cover Art Archive thumbnails (/front-250) to the bare /front original — but
/front redirects to archive.org, which is unreliable: probing release-group
covers showed intermittent HTTP 500s (same URL 500s one second, serves the
next) and multi-MB originals (2.9 MB seen). The result was the user-reported
flakiness: cover art that "sometimes works, sometimes shows nothing", and a
huge image embedded into every track when it did work.
The sized thumbnails (/front-250, -500, -1200) are served by CAA's own CDN,
not the archive.org redirect — which is why /front-250 (240p) was always
reliable. Upgrade to /front-1200 instead: 1200x1200 is a massive jump from
240p, reliably CDN-served, and a sane ~40 KB instead of multi-MB.
Applied in all three CAA spots for consistency: the _upgrade_art_url helper
(embed + cover.jpg paths) and both prefer_caa ("CCA") blocks, which fetched
the bare /front directly with no fallback — so CCA-on users hit the same
flakiness. _fetch_art_bytes still falls back to the original /front-250 if
/front-1200 is ever refused.
Tests updated to assert the 1200px target, idempotency, and that the bare
/front original is intentionally left untouched.
abdea631a7