Reopening a library (or opening another one, or set_disk_cache_bytes
falling back to attaching) replaced MediaCache::rendered with a new
PreviewCache, but render jobs still in flight kept the old object.
Each PreviewCache checked only its own generation, so after a clear on
the new cache the old one's generation was still current: a finishing
thumbnail job wrote its pixels through it into the directory the clear
had just emptied. The UI rejected the result, but the JPEG stayed.
attach_disk_cache now retires the cache it replaces before swapping it:
PreviewCache::retire takes the generation write lock (so it waits for a
write in progress, like clear) and marks the object retired; every
get/put/put_deferred through it is then refused and its clear() is a
no-op, as its directory may now belong to the replacement. Files on
disk are left alone, so a plain reopen still finds its thumbnails, and
resizing the budget in place keeps the same cache object as before.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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