The main thread's Workers tracked no rendered-thumbnail cache until the
first render request carried one. If Clear Preview Cache ran before that
(e.g. starting on an empty filtered view), the per-frame observation in
finished() had nothing to compare with, and the first request only
recorded the already-cleared generation as its baseline. The persisted
ThumbIndex was never invalidated, so once the filter was removed the
request touched the old entry and the worker read the pre-clear JPEG
back from browser storage. Replacing the cache (another library) before
the first request had the same gap.
Workers::start now takes the session's cache and records it, with its
current generation, as the baseline the persisted index belongs to. A
normal start with no clear observes the same cache and generation and
keeps the index. The comparison moves into wire::CacheWatch so it is
tested natively (cargo test --workspace) next to ThumbIndex.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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