Timeline's items array used to rebuild on every sub-pixel cellSize tick
during the sidebar CSS transition, causing visible jank with thousands
of photos. Row heights now resolve off a ref at virtualizer-measure
time, so items only rebuild when the column count actually changes.
PreviewFilmstrip is horizontally virtualised (~15 cells in the DOM
instead of N), cutting preview open latency on large libraries. Also
honor the user's explicit right-sidebar collapse (don't auto-reopen on
photo selection) and shrink the sonner toasts to a tighter form factor.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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