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Merged
juliusmarminge merged 4 commits into from
Aug 7, 2026
Merged

fix(web): stabilize chat timeline positioning #5449

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e640034
bump web legend list to 3.3.3
jmeistrich Aug 5, 2026
79b89e9
fix: stabilize chat timeline anchoring
jmeistrich Aug 5, 2026
5fa2e03
fix: preserve timeline position during disclosure toggles
jmeistrich Aug 5, 2026
1072164
fix: preserve sent message anchor during manual scroll
jmeistrich Aug 5, 2026
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2 changes: 1 addition & 1 deletion apps/web/package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,7 @@
"@dnd-kit/utilities": "^3.2.2",
"@effect/atom-react": "catalog:",
"@formkit/auto-animate": "^0.9.0",
"@legendapp/list": "3.2.0",
"@legendapp/list": "3.3.3",
"@lexical/react": "^0.41.0",
"@pierre/diffs": "catalog:",
"@pierre/trees": "1.0.0-beta.4",
Expand Down
136 changes: 32 additions & 104 deletions apps/web/src/components/ChatView.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -3527,12 +3527,8 @@ function ChatViewContent(props: ChatViewProps) {
const activeTimelineAnchorIndexRef = useRef<number | null>(null);
const anchorUserScrollGenerationRef = useRef(0);
const liveFollowUserScrollGenerationRef = useRef<number | null>(0);
const pendingAnchorScrollRestoreRef = useRef<{
readonly messageId: MessageId;
readonly offset: number;
readonly userScrollGeneration: number;
} | null>(null);
const anchorScrollRestoreFrameRef = useRef<number | null>(null);
// 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(() => {
anchorUserScrollGenerationRef.current += 1;
timelineScrollModeRef.current = "free-scrolling";
Expand All @@ -3542,11 +3538,6 @@ function ChatViewContent(props: ChatViewProps) {
positionedTimelineAnchorRef.current = null;
settledTimelineAnchorRef.current = null;
activeTimelineAnchorIndexRef.current = null;
pendingAnchorScrollRestoreRef.current = null;
if (anchorScrollRestoreFrameRef.current !== null) {
cancelAnimationFrame(anchorScrollRestoreFrameRef.current);
anchorScrollRestoreFrameRef.current = null;
}
}, []);
const cancelTimelineLiveFollowForUserNavigationRef = useRef(
cancelTimelineLiveFollowForUserNavigation,
Expand Down Expand Up @@ -3602,7 +3593,6 @@ function ChatViewContent(props: ChatViewProps) {
},
[composerOverlayHeight],
);

// Live-follow stays active after send/thread-open until an actual list scroll
// gesture opts out.
const scrollToEnd = useCallback((animated = false) => {
Expand All @@ -3614,7 +3604,12 @@ function ChatViewContent(props: ChatViewProps) {
activeTimelineAnchorIndexRef.current = null;
showScrollDebouncer.current.cancel();
setShowScrollToBottom(false);
void legendListRef.current?.scrollToEnd?.({ animated });
setTimelineAnchor((current) =>
current.messageId === null ? current : { ...current, messageId: null },
);
requestAnimationFrame(() => {
void legendListRef.current?.scrollToEnd?.({ animated });
});
}, []);
useEffect(() => {
let removeListeners: (() => void) | null = null;
Expand Down Expand Up @@ -3753,75 +3748,23 @@ function ChatViewContent(props: ChatViewProps) {
}
return;
}
const scrollNode = list.getScrollableNode();
let finished = false;
const finishAnimatedPositioning = () => {
if (finished) {
return;
}
finished = true;
window.clearTimeout(fallbackTimer);
scrollNode.removeEventListener("scrollend", finishAnimatedPositioning);
if (positionedTimelineAnchorRef.current !== messageId) {
return;
}
const scrollOffset = list.getState().scroll;
void list.scrollToOffset({ offset: scrollOffset, animated: false });
settledTimelineAnchorRef.current = messageId;
};
const fallbackTimer = window.setTimeout(finishAnimatedPositioning, 750);
scrollNode.addEventListener("scrollend", finishAnimatedPositioning, { once: true });
void list.scrollToIndex({
index: anchorIndex,
animated: true,
viewPosition: 0,
viewOffset: CHAT_LIST_ANCHOR_OFFSET,
});
void list
.scrollToIndex({
index: anchorIndex,
animated: true,
viewPosition: 0,
viewOffset: CHAT_LIST_ANCHOR_OFFSET,
})
.then(() => {
if (positionedTimelineAnchorRef.current !== messageId) {
return;
}
settledTimelineAnchorRef.current = messageId;
});
});
};
requestAnimationFrame(() => positionAnchor(12));
}, []);
const onTimelineAnchorSizeChanged = useCallback((messageId: MessageId) => {
if (settledTimelineAnchorRef.current !== messageId) {
return;
}
if (liveFollowUserScrollGenerationRef.current === anchorUserScrollGenerationRef.current) {
return;
}
const scrollOffset = legendListRef.current?.getState().scroll;
if (scrollOffset === undefined) {
return;
}
if (pendingAnchorScrollRestoreRef.current === null) {
pendingAnchorScrollRestoreRef.current = {
messageId,
offset: scrollOffset,
userScrollGeneration: anchorUserScrollGenerationRef.current,
};
}
if (anchorScrollRestoreFrameRef.current !== null) {
return;
}
anchorScrollRestoreFrameRef.current = requestAnimationFrame(() => {
anchorScrollRestoreFrameRef.current = null;
const pending = pendingAnchorScrollRestoreRef.current;
pendingAnchorScrollRestoreRef.current = null;
if (
pending &&
settledTimelineAnchorRef.current === pending.messageId &&
pending.userScrollGeneration === anchorUserScrollGenerationRef.current
) {
const list = legendListRef.current;
const currentScrollOffset = list?.getState().scroll;
if (
typeof currentScrollOffset === "number" &&
Math.abs(currentScrollOffset - pending.offset) <= 2
) {
void list?.scrollToOffset({ offset: pending.offset, animated: false });
}
}
});
}, []);

const onIsAtEndChange = useCallback((isAtEnd: boolean) => {
if (
Expand All @@ -3847,13 +3790,19 @@ function ChatViewContent(props: ChatViewProps) {
}
}, []);

// Anchored end space intentionally disables LegendList's normal end-follow so
// the sent message can stay near the top. T3 only owns streaming adjustments
// during that mode; LegendList owns ordinary end-follow everywhere else.
useEffect(() => {
if (!activeThread?.id) {
return;
}
if (liveFollowUserScrollGenerationRef.current !== anchorUserScrollGenerationRef.current) {
return;
}
if (timelineScrollModeRef.current !== "anchoring-new-turn") {
return;
}

let secondFrame: number | null = null;
const frame = requestAnimationFrame(() => {
Expand All @@ -3875,28 +3824,13 @@ function ChatViewContent(props: ChatViewProps) {
return;
}

if (timelineScrollModeRef.current === "anchoring-new-turn") {
const metrics = getActiveTimelineTurnMetrics(list);
if (!metrics) {
return;
}
if (metrics.scrollDeltaToRevealEnd <= 1) {
return;
}

const nextOffset = list.getState().scroll + metrics.scrollDeltaToRevealEnd;
void list.scrollToOffset({ offset: nextOffset, animated: false });
return;
}

if (timelineScrollModeRef.current !== "following-end") {
return;
}
if (!timelineRealContentOverflowsViewport(list)) {
const metrics = getActiveTimelineTurnMetrics(list);
if (!metrics || metrics.scrollDeltaToRevealEnd <= 1) {
return;
}

void list.scrollToEnd?.({ animated: false });
const nextOffset = list.getState().scroll + metrics.scrollDeltaToRevealEnd;
void list.scrollToOffset({ offset: nextOffset, animated: false });
});
});

Expand All @@ -3906,12 +3840,7 @@ function ChatViewContent(props: ChatViewProps) {
cancelAnimationFrame(secondFrame);
}
};
}, [
activeThread?.id,
timelineEntries,
getActiveTimelineTurnMetrics,
timelineRealContentOverflowsViewport,
]);
}, [activeThread?.id, timelineEntries, getActiveTimelineTurnMetrics]);

useEffect(() => {
setPullRequestDialogState(null);
Expand Down Expand Up @@ -6103,7 +6032,6 @@ function ChatViewContent(props: ChatViewProps) {
skills={activeProviderStatus?.skills ?? EMPTY_PROVIDER_SKILLS}
anchorMessageId={timelineAnchorMessageId}
onAnchorReady={onTimelineAnchorReady}
onAnchorSizeChanged={onTimelineAnchorSizeChanged}
contentInsetEndAdjustment={composerOverlayHeight}
liveFollowEnabled={timelineLiveFollowEnabled}
onIsAtEndChange={onIsAtEndChange}
Expand Down
14 changes: 7 additions & 7 deletions apps/web/src/components/chat/MessagesTimeline.test.tsx
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,6 @@ vi.mock("@legendapp/list/react", async () => {
anchorMaxSize?: number;
anchorOffset?: number;
onReady?: (info: { anchorIndex: number }) => void;
onSizeChanged?: (size: number) => void;
};
contentInsetEndAdjustment?: number;
className?: string;
Expand All @@ -42,7 +41,6 @@ vi.mock("@legendapp/list/react", async () => {
ref?: Ref<LegendListRef>;
}) => {
if (props.anchoredEndSpace) {
props.anchoredEndSpace.onSizeChanged?.(240);
props.anchoredEndSpace.onReady?.({ anchorIndex: props.anchoredEndSpace.anchorIndex });
}
return (
Expand Down Expand Up @@ -90,6 +88,11 @@ vi.mock("@legendapp/list/react", async () => {
? props.maintainVisibleContentPosition.size
: undefined
}
data-maintain-visible-content-position-restore={
typeof props.maintainVisibleContentPosition === "object"
? Boolean(props.maintainVisibleContentPosition.shouldRestorePosition)
: undefined
}
>
{props.ListHeaderComponent}
{props.data.map((item) => (
Expand Down Expand Up @@ -192,7 +195,6 @@ function buildProps() {
workspaceRoot: undefined,
anchorMessageId: null,
onAnchorReady: () => {},
onAnchorSizeChanged: () => {},
contentInsetEndAdjustment: 0,
liveFollowEnabled: true,
onIsAtEndChange: () => {},
Expand Down Expand Up @@ -386,7 +388,6 @@ describe("MessagesTimeline", () => {

it("anchors a sent attachment message using its measured height", () => {
const onAnchorReady = vi.fn();
const onAnchorSizeChanged = vi.fn();
const firstEntry = buildUserTimelineEntry("First prompt.");
const secondEntry = {
...buildUserTimelineEntry("Newest prompt."),
Expand All @@ -411,7 +412,6 @@ describe("MessagesTimeline", () => {
{...buildProps()}
anchorMessageId={secondEntry.message.id}
onAnchorReady={onAnchorReady}
onAnchorSizeChanged={onAnchorSizeChanged}
contentInsetEndAdjustment={144}
timelineEntries={[firstEntry, secondEntry]}
/>,
Expand All @@ -426,10 +426,10 @@ describe("MessagesTimeline", () => {
expect(markup).not.toContain('data-maintain-scroll-at-end="enabled"');
expect(markup).toContain('data-maintain-visible-content-position="object"');
expect(markup).toContain('data-maintain-visible-content-position-data="true"');
expect(markup).toContain('data-maintain-visible-content-position-size="false"');
expect(markup).toContain('data-maintain-visible-content-position-size="true"');
expect(markup).toContain('data-maintain-visible-content-position-restore="true"');
expect(onAnchorReady).toHaveBeenCalledOnce();
expect(onAnchorReady).toHaveBeenCalledWith(secondEntry.message.id, 1);
expect(onAnchorSizeChanged).toHaveBeenCalledWith(secondEntry.message.id, 240);
});

it("renders collapse controls for long user messages", () => {
Expand Down
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