fix: prevent detail flash on close with fill forwards and rAF cancel#11419
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Two fixes to eliminate a one-frame flash when closing the detail: 1. Add fill: 'forwards' to Web Animations — keeps the final keyframe applied after the animation finishes, preventing the CSS resting state (translate: none from has-detail) from showing between animation end and the finished Promise resolution. Cleaned up when __endTransition cancels the animation, after the callback has already cleared has-detail. 2. Cancel pending ResizeObserver rAF in __endTransition — during the closing animation, ResizeObserver can capture stale layout state (hasDetail: true) into a deferred rAF that would re-apply has-detail on the next frame. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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vursen
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Mar 28, 2026
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Summary
Two fixes to eliminate a one-frame flash when closing the detail panel:
fill: 'forwards'on Web Animations — keeps the final keyframe applied after the animation finishes, preventing the CSS resting state (translate: nonefromhas-detail) from showing between animation end and thefinishedPromise resolution. The fill effect is cleaned up when__endTransitioncancels the animation, which happens after the callback has already clearedhas-detail.cancelAnimationFrame(this.__resizeRaf)in__endTransition— during the closing animation,ResizeObservercan fire and capture stale layout state (hasDetail: true) into a deferredrequestAnimationFrame. When the animation finishes, the callback correctly clearshas-detail, but the stale rAF would re-apply it on the next frame. Cancelling it in__endTransitionprevents the stale state from overwriting the correct post-transition state.Both fixes are needed:
fill: 'forwards'bridges the synchronous gap between animation end and Promise resolution, while the rAF cancel prevents the asynchronous ResizeObserver race.Test plan
yarn test --group master-detail-layout— all tests pass🤖 Generated with Claude Code