fix(virtual-core): viewport drifts when above-viewport rows resize over multiple frames#1212
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piecyk merged 1 commit intoJun 30, 2026
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…er multiple frames Folding adjustments eagerly into `scrollOffset` means the browser's scroll event for an adjustment write now arrives at exactly the offset we already hold, and the direction computation classified that equality as `'backward'`. With `isScrolling` held for `isScrollingResetDelay` after the event, the default `shouldAdjustScrollPositionOnItemSizeChange` then skipped every above-viewport re-measure compensation until the reset — so multi-frame reflows (a side pane's width animation re-wrapping rows while the user is scrolled up) drifted the viewport, with only ~1 frame in 9 compensated. An event at the held offset carries no directional information, so keep the previous direction for it instead of computing the comparison. Real gestures still latch normally (their read-backs never equal the held offset, which moves with each event), an equality read-back during a real backward gesture correctly stays `'backward'`, and the `isScrolling === false` reset emission still clears the direction.
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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🎯 Changes
Folding adjustments eagerly into
scrollOffsetmeans the browser's scroll event for an adjustment write now arrives at exactly the offset we already hold, and the direction computation classified that equality as'backward'. WithisScrollingheld forisScrollingResetDelayafter the event, the defaultshouldAdjustScrollPositionOnItemSizeChangethen skipped every above-viewport re-measure compensation until the reset — so multi-frame reflows (a side pane's width animation re-wrapping rows while the user is scrolled up) drifted the viewport, with only ~1 frame in 9 compensated.An event at the held offset carries no directional information, so keep the previous direction for it instead of computing the comparison. Real gestures still latch normally (their read-backs never equal the held offset, which moves with each event), an equality read-back during a real backward gesture correctly stays
'backward', and theisScrolling === falsereset emission still clears the direction.✅ Checklist
pnpm run test:pr.🚀 Release Impact
This PR was assisted by Claude Code.
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