library.buildPreviews {size: standard (Settings → Performance preview size) | full, ids?,
wait?} renders each photo's grid thumbnail and loupe view into the memory + disk preview cache
(selected photos, else all in view) on a background thread; library.previewProgress /
cancelPreviews. File ▸ Previews: Build Standard-Sized / 1:1, Stop, Discard Preview Cache;
toasts when a build starts and finishes. Also silences the wasm-only unused `threads` warning.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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