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npub1mn7jgtj4w2pd0g0zeuhxsa6jy6p0rewxz4kujt98my82ahfmp72sxjexk7andWill Pfleger
b0426006b5
Loading older messages under virtualization let three writers fight over scrollTop on overlapping frames, so the anchored row jittered or collapsed to the top (~33% of prepends) and the library's reconcile spun the full 5s MAX_RECONCILE_MS valve. Establish a single owner of scroll position across the whole fetch+restore window: - useLoadOlderOnScroll restores by scrollTop ONLY (drop scrollToIndex), via one getOffsetForIndex(anchorIndex + prepended, "start")[0] + intra-row gap write. getOffsetForIndex is a pure measurement-cache read, so no library scrollState is set and the reconcile loop has nothing to fight. - The viewport ResizeObserver in useTimelineScrollManager no longer runs a competing restore during a fetch: it skips while isFetchingOlder is true (the spinner's clientHeight 720->590 mount-shift fires before the lock is set) and otherwise defers to lockedScrollTopRef when the load-older restore holds it. MessageTimeline threads isFetchingOlder into the manager. The defect was invisible to unit tests (jsdom getBoundingClientRect -> 0) and to static traces; the new load-older E2E drives a real prepend on six fresh page loads and asserts the anchor holds every run, the scroller genuinely grew, and the reconcile terminates. emitMockHistory now honors the relay filter's until/limit so the mock relay paginates like a real one, which the E2E needs to exercise a genuine older page. Co-authored-by: Will Pfleger <pfleger.will@gmail.com> Signed-off-by: Will Pfleger <pfleger.will@gmail.com>