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fix(web): scroll-to-end button no longer jumps up and down #26375

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Merged
t3dotgg merged 1 commit into from
Oct 28, 2026
Merged

fix(web): scroll-to-end button no longer jumps up and down #26375

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23 changes: 23 additions & 0 deletions apps/web/src/components/chat/MessagesTimeline.browser.test.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -205,6 +205,29 @@ describe("MessagesTimeline messages", () => {
expect(maxNestedCommits).toBeLessThan(20);
});

it("keeps reporting overflow while the composer inset changes", async () => {
setup();
const props = baseProps();
const overflowReports: boolean[] = [];
const replies = Array.from({ length: 40 }, (_, index) =>
message(`Reply ${index}\n\n${"line\n\n".repeat(8)}`, { role: "assistant" }, `r-${index}`),
);
const timeline = (inset: number) => (
<MessagesTimeline
{...props}
timelineEntries={replies}
contentInsetEndAdjustment={inset}
onContentOverflowChange={(overflows) => overflowReports.push(overflows)}
/>
);
await using screen = await renderElement(timeline(110));
await vi.waitFor(() => expect(overflowReports.at(-1)).toBe(true));
overflowReports.length = 0;
// The resting composer resizes with overflow; a false report here flips it back.
await screen.rerender(timeline(148));
expect(overflowReports).not.toContain(false);
});

it("keeps the first and last message headings reachable from either end", async () => {
setup();
const props = baseProps();
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6 changes: 4 additions & 2 deletions apps/web/src/components/chat/MessagesTimeline.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -1144,7 +1144,9 @@ const ConversationTimeline = memo(function ConversationTimeline({

const canvas = useChatCanvas();
const registerTimeline = canvas?.registerTimeline;
const setTimelineList = (list: LegendListRef | null) => {
// Stable so the list attaches once per mount. A re-attach reports no overflow for a frame,
// which flips the resting composer, resizes it, and re-renders this list again.
const setTimelineList = useStableCallback((list: LegendListRef | null) => {
listRef.current = list;
const scrollNode: HTMLElement | null = list?.getScrollableNode() ?? null;
registerTimeline?.(scrollNode);
Expand Down Expand Up @@ -1190,7 +1192,7 @@ const ConversationTimeline = memo(function ConversationTimeline({
listRef.current = null;
registerTimeline?.(null);
};
};
});

useThreadFindPositionReader({
threadKey: listIdentityKey,
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