fix(web): stop zero-height measurements from desyncing virtualized lists - #943
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sheepbox8646 wants to merge 1 commit into
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fix(web): stop zero-height measurements from desyncing virtualized lists#943sheepbox8646 wants to merge 1 commit into
sheepbox8646 wants to merge 1 commit into
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Rows in measured-row virtualizers (sidebar Recents, model pickers) can be (re)measured while they cannot be laid out — their pane is display:none behind a v-show'd sidebar view, or the node was just detached by a window shift. Those measurements report height 0, and recording them poisons the virtualizer twice over: the spacer collapses, and the later 0-to-real re-measure runs scroll compensation on an element whose scrollTop cannot move, walking the virtualizer's internal offset away from the element's real scrollTop one row at a time. Recents then opens with a dead gap at the top and only the oldest sessions visible until a real scroll event resyncs it. Add measureVirtualRow, a shared measureElement guard that treats a zero-height measurement as "unmeasurable right now" and keeps the last known row size, and wire it into the three measured-row virtualizers. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Problem
The sidebar Recents list would randomly open with a dead gap below the header and only the oldest sessions visible — newly created sessions seemed to disappear. A re-login (full reload) fixed it temporarily; it later came back. Reproduced deterministically on a dev bot's initial load.
Root cause
Rows in measured-row virtualizers can be (re)measured while they cannot be laid out — their pane is
display:nonebehind av-show'd sidebar view, or the node was just detached by a virtualizer window shift. Those measurements report height 0 and get written into@tanstack/vue-virtual'sitemSizeCache.That poisons the virtualizer twice over:
applyScrollAdjustmentassumes theelement.scrollTo()landed and bumps the internal offset anyway, one row height at a time (observed +36px × 18 rows → internal offset 648 while the real scrollTop stayed 0).The virtualizer then renders its window mid-list: a dead gap at the top where the newest sessions belong, only the tail rows painted. Any real scroll event resyncs it, which is why the bug looked random and self-healing.
Fix
Add
measureVirtualRow(apps/web/src/utils/virtual-row-measure.ts), a sharedmeasureElementguard: a zero-height measurement means "unmeasurable right now", so keep the last known size (or the estimate) instead of recording 0. Wired into the three measured-row virtualizers:components/sidebar/recents.vue(the reported list)components/searchable-select-popover/index.vuepages/bots/components/model-options.vueVerification
/bot/helloreproduced on first load (first rendered row index 14 at translateY 288, six 0-height cache entries, +36 adjustment cascade in the scroll log); after the fix, row 0 renders at y=0, full scrollHeight restored, and scroll-to-bottom / panel switch away+back / bot switch while the pane is hidden all stay clean.measureVirtualRow; existing sidebar + chat-list suites pass (139 tests);vue-tsc, ESLint, and the UI contract guard are clean.🤖 Generated with Claude Code