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Bohan Jiang
b9bf2653be
Follow-up to #3196. Switching tabs and back on a long issue still landed at scrollTop=0 because issue-detail uses Virtuoso with customScrollParent — Virtuoso wires its scroll/resize observers in a passive useEffect, which fires *after* useLayoutEffect. So at the moment the restore hook ran, the spacer that gives the scroll container its tall scrollHeight hadn't been re-established yet (scrollHeight === clientHeight), and the browser silently clamped `scrollTop = saved` down to 0. Diagnostic console output confirmed this: marker key=true saved=10356.5 currentScrollTop=0 scrollHeight=750 clientHeight=750 → set scrollTop to 10356.5 actually now 0 Fix: keep the synchronous set as the fast path, then if the assignment was clamped, retry across rAF frames for up to ~500ms (30 frames at 60fps). That gives Virtuoso's passive effect time to re-establish the spacer, after which the next tick succeeds. Cancel any in-flight retry when the effect tears down (Activity hidden again or component unmount). Existing 4 tests in use-tab-scroll-restore.test.tsx still pass — the synchronous fast path covers the simple-content case they exercise. A jsdom regression for the Virtuoso scenario didn't reproduce reliably (the clamp + rAF interplay needs a real browser), so this relies on manual verification: open issue-detail, scroll deep into comments, switch tabs, switch back — scroll position now holds.