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perf(web): switching threads no longer re-renders the outgoing thread's rows #21123

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Merged
juliusmarminge merged 1 commit into from
Oct 18, 2026
Merged

perf(web): switching threads no longer re-renders the outgoing thread's rows #21123

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170 changes: 88 additions & 82 deletions apps/web/src/components/chat/MessagesTimeline.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -1374,13 +1374,21 @@ const ConversationTimeline = memo(function ConversationTimeline({
contentInsetEndAdjustment,
});

// Each row carries its own provider. LegendList moves rows into their
// containers one commit after this component renders, so a provider around
// the list would re-render the outgoing thread's rows with the incoming
// thread's context just before they unmount. extraData hands a changed
// sharedState to the rows that stay.
const renderItem = ({ item }: { item: MessagesTimelineRow }) => (
<div className="messages-timeline-row-frame">
<div className="chat-content-lane overflow-x-clip" data-timeline-root="true">
<TimelineRowContent row={item} />
<TimelineRowCtx value={sharedState}>
<div className="messages-timeline-row-frame">
<div className="chat-content-lane overflow-x-clip" data-timeline-root="true">
<TimelineRowContent row={item} />
</div>
</div>
</div>
</TimelineRowCtx>
);
const listExtraData = { identity: listIdentityKey, rowCount: rows.length, sharedState };

const forwardMinimapWheel = (event: WheelEvent) => {
const scrollNode = listRef.current?.getScrollableNode();
Expand Down Expand Up @@ -1411,85 +1419,83 @@ const ConversationTimeline = memo(function ConversationTimeline({

return (
<MarkdownFindContext value={findActive}>
<TimelineRowCtx value={sharedState}>
<TimelineRowActivityCtx value={activityState}>
<TooltipScrollDismissArea
ref={setTimelineViewportElement}
className="relative h-full min-h-0"
data-assistant-citation-viewport="true"
>
{onCiteAssistantText && citationThreadRef ? (
<AssistantSelectionToolbar
viewport={timelineViewportElement}
threadRef={citationThreadRef}
onCite={onCiteAssistantText}
/>
) : null}
<LegendList<MessagesTimelineRow>
ref={setTimelineList}
data={rows}
extraData={`${listIdentityKey}:${rows.length}`}
keyExtractor={keyExtractor}
getItemType={getItemType}
renderItem={renderItem}
estimatedItemSize={90}
initialScrollAtEnd={
!findActive && citationRequest === null && rememberedPosition?.atEnd !== false
}
// Legend needs a data refresh to mount new pins without a scroll event.
dataVersion={readyCitationRequest?.key ?? listIdentityKey}
{...(alwaysRender ? { alwaysRender } : {})}
onLoad={handleListLoad}
{...(anchoredEndSpace ? { anchoredEndSpace } : {})}
contentInsetEndAdjustment={anchoredEndSpace ? contentInsetEndAdjustment : 0}
maintainScrollAtEnd={
citationPositioning ||
(restoringThreadPosition && rememberedPosition?.atEnd === false) ||
anchoredEndSpace ||
!liveFollowEnabled ||
fullscreenAppRowId !== null ||
disclosureToggleSettling
? false
: isWorking && !prefersReducedMotion && settlingListIdentity === null
? TIMELINE_MAINTAIN_SCROLL_AT_END_SMOOTH
: TIMELINE_MAINTAIN_SCROLL_AT_END
}
maintainVisibleContentPosition={
findActive ||
citationPositioning ||
(restoringThreadPosition && rememberedPosition?.atEnd === false)
? false
: maintainVisibleContentPosition
}
maintainScrollAtEndThreshold={1}
onScroll={handleScroll}
onItemSizeChanged={handleItemSizeChanged}
className={cn(
"messages-timeline-scroll scrollbar-gutter-both h-full min-h-0 overflow-x-hidden overscroll-y-contain [overflow-anchor:none]",
topFadeEnabled && "topbar-scroll-fade",
)}
ListHeaderComponent={listHeader}
ListFooterComponent={timelineListFooter}
/>
<TimelineMinimap
items={minimapItems}
hasPersistentGutter={minimapHasPersistentGutter}
hitStripWidth={minimapHitStripWidth}
currentIndex={minimapCurrentIndex}
stripMap={minimapStripMap}
onWheel={forwardMinimapWheel}
onSelect={(item) => {
onManualNavigation();
void listRef.current?.scrollToIndex({
index: item.rowIndex,
animated: true,
viewOffset: 24,
});
}}
<TimelineRowActivityCtx value={activityState}>
<TooltipScrollDismissArea
ref={setTimelineViewportElement}
className="relative h-full min-h-0"
data-assistant-citation-viewport="true"
>
{onCiteAssistantText && citationThreadRef ? (
<AssistantSelectionToolbar
viewport={timelineViewportElement}
threadRef={citationThreadRef}
onCite={onCiteAssistantText}
/>
</TooltipScrollDismissArea>
</TimelineRowActivityCtx>
</TimelineRowCtx>
) : null}
<LegendList<MessagesTimelineRow>
ref={setTimelineList}
data={rows}
extraData={listExtraData}
keyExtractor={keyExtractor}
getItemType={getItemType}
renderItem={renderItem}
estimatedItemSize={90}
initialScrollAtEnd={
!findActive && citationRequest === null && rememberedPosition?.atEnd !== false
}
// Legend needs a data refresh to mount new pins without a scroll event.
dataVersion={readyCitationRequest?.key ?? listIdentityKey}
{...(alwaysRender ? { alwaysRender } : {})}
onLoad={handleListLoad}
{...(anchoredEndSpace ? { anchoredEndSpace } : {})}
contentInsetEndAdjustment={anchoredEndSpace ? contentInsetEndAdjustment : 0}
maintainScrollAtEnd={
citationPositioning ||
(restoringThreadPosition && rememberedPosition?.atEnd === false) ||
anchoredEndSpace ||
!liveFollowEnabled ||
fullscreenAppRowId !== null ||
disclosureToggleSettling
? false
: isWorking && !prefersReducedMotion && settlingListIdentity === null
? TIMELINE_MAINTAIN_SCROLL_AT_END_SMOOTH
: TIMELINE_MAINTAIN_SCROLL_AT_END
}
maintainVisibleContentPosition={
findActive ||
citationPositioning ||
(restoringThreadPosition && rememberedPosition?.atEnd === false)
? false
: maintainVisibleContentPosition
}
maintainScrollAtEndThreshold={1}
onScroll={handleScroll}
onItemSizeChanged={handleItemSizeChanged}
className={cn(
"messages-timeline-scroll scrollbar-gutter-both h-full min-h-0 overflow-x-hidden overscroll-y-contain [overflow-anchor:none]",
topFadeEnabled && "topbar-scroll-fade",
)}
ListHeaderComponent={listHeader}
ListFooterComponent={timelineListFooter}
/>
<TimelineMinimap
items={minimapItems}
hasPersistentGutter={minimapHasPersistentGutter}
hitStripWidth={minimapHitStripWidth}
currentIndex={minimapCurrentIndex}
stripMap={minimapStripMap}
onWheel={forwardMinimapWheel}
onSelect={(item) => {
onManualNavigation();
void listRef.current?.scrollToIndex({
index: item.rowIndex,
animated: true,
viewOffset: 24,
});
}}
/>
</TooltipScrollDismissArea>
</TimelineRowActivityCtx>
</MarkdownFindContext>
);
});
Expand Down
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