The CAA proxy was caching all fetch failures (including 503s and
timeouts) as empty files, treating them as permanent 'no art' misses.
During Internet Archive outages, this meant every album got cached
as having no cover art, and the cache persisted after IA recovered.
Now only 404 responses (no cover art exists) are cached as permanent
misses. 503, timeouts, and other transient errors are not cached,
so the next request retries the fetch.
Also cleared 33 incorrectly cached 0-byte miss files from a
concurrent IA outage.
yonlu
d5f34f242f