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fix(web): preserve thread reading positions #12144

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Merged
maria-rcks merged 2 commits into from
Sep 17, 2026
Merged

fix(web): preserve thread reading positions #12144

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a2a1053
fix(web): preserve thread reading positions
maria-rcks Sep 16, 2026
dc94cb8
fix(web): let navigation cancel thread restoration
maria-rcks Sep 16, 2026
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35 changes: 14 additions & 21 deletions apps/web/src/components/ChatView.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,7 @@ import { type LegendListRef } from "@legendapp/list/react";
import {
CHAT_TIMELINE_ANCHOR_OFFSET,
getAnchoredTurnMetrics,
readTimelinePosition,
timelineContentOverflowsViewport,
type TimelineScrollMode,
} from "./chat/timelineScrollAnchoring";
Expand Down Expand Up @@ -5222,10 +5223,12 @@ export default function ChatView(props: ChatViewProps) {
const settledTimelineAnchorRef = useRef<MessageId | null>(null);
const activeTimelineAnchorIndexRef = useRef<number | null>(null);
const anchorUserScrollGenerationRef = useRef(0);
const cancelPositionRestoreRef = useRef<(() => void) | null>(null);
const liveFollowUserScrollGenerationRef = useRef<number | null>(0);
// Manual navigation stops live-follow without removing anchored end space.
// Collapsing that space during a gesture clamps the viewport back to the end.
const cancelTimelineLiveFollowForUserNavigation = useCallback(() => {
cancelPositionRestoreRef.current?.();
anchorUserScrollGenerationRef.current += 1;
timelineScrollModeRef.current = "free-scrolling";
liveFollowUserScrollGenerationRef.current = null;
Expand Down Expand Up @@ -5305,6 +5308,7 @@ export default function ChatView(props: ChatViewProps) {
// Live-follow stays active after send/thread-open until an actual list scroll
// gesture opts out.
const scrollToEnd = useCallback((animated = false) => {
cancelPositionRestoreRef.current?.();
isAtEndRef.current = true;
timelineScrollModeRef.current = "following-end";
liveFollowUserScrollGenerationRef.current = anchorUserScrollGenerationRef.current;
Expand All @@ -5320,21 +5324,6 @@ export default function ChatView(props: ChatViewProps) {
void legendListRef.current?.scrollToEnd?.({ animated });
});
}, []);
const displayedTimelineKeyRef = useRef(displayedTimeline.displayThreadKey);
useLayoutEffect(() => {
const displayKey = displayedTimeline.displayThreadKey;
if (displayKey === null || displayKey !== activeThreadKey) {
displayedTimelineKeyRef.current = displayKey;
return;
}
if (displayedTimelineKeyRef.current === displayKey) {
return;
}
displayedTimelineKeyRef.current = displayKey;
// Keep the list mounted across jumps; pin the newly displayed thread to
// its end the way a remount used to via initialScrollAtEnd.
scrollToEnd();
}, [activeThreadKey, displayedTimeline.displayThreadKey, scrollToEnd]);
useLayoutEffect(() => {
if (timelineScrollModeRef.current !== "anchoring-new-turn") {
return;
Expand Down Expand Up @@ -5644,19 +5633,22 @@ export default function ChatView(props: ChatViewProps) {

useEffect(() => {
setPullRequestDialogState(null);
isAtEndRef.current = true;
const followEnd = readTimelinePosition(routeThreadKey)?.atEnd !== false;
isAtEndRef.current = followEnd;
timelineScrollIntentRef.current = null;
timelineScrollModeRef.current = "following-end";
liveFollowUserScrollGenerationRef.current = anchorUserScrollGenerationRef.current;
setTimelineLiveFollowEnabled(true);
timelineScrollModeRef.current = followEnd ? "following-end" : "free-scrolling";
liveFollowUserScrollGenerationRef.current = followEnd
? anchorUserScrollGenerationRef.current
: null;
setTimelineLiveFollowEnabled(followEnd);
pendingTimelineAnchorRef.current = null;
positionedTimelineAnchorRef.current = null;
settledTimelineAnchorRef.current = null;
activeTimelineAnchorIndexRef.current = null;
showScrollDebouncer.current.cancel();
setShowScrollToBottom(false);
setShowScrollToBottom(!followEnd);
// activeThreadRef resets transitively with the active thread.
}, [activeThread?.id]);
}, [activeThread?.id, routeThreadKey]);

useEffect(() => {
if (!activeThread?.id || terminalUiState.terminalOpen) return;
Expand Down Expand Up @@ -9513,6 +9505,7 @@ export default function ChatView(props: ChatViewProps) {
onContentOverflowChange={setTimelineOverflows}
onToolOutputCollapsedAtEnd={onToolOutputCollapsedAtEnd}
onManualNavigation={cancelTimelineLiveFollowForUserNavigation}
cancelPositionRestoreRef={cancelPositionRestoreRef}
hideEmptyPlaceholder={isDraftHeroState || threadDetailLoading}
topFadeEnabled={!hasTimelineTopBanner}
loadEarlier={paintOnlyDisplayedTimeline ? null : loadEarlierTurns}
Expand Down
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