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fix(web-ui): stabilize FlowChat history paging #1925

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Merged
wsp1911 merged 1 commit into from
Jul 31, 2026
Merged

fix(web-ui): stabilize FlowChat history paging #1925

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29 changes: 29 additions & 0 deletions src/web-ui/src/flow_chat/components/modern/VirtualMessageList.scss
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,30 @@
overflow-wrap: anywhere;
pointer-events: none;
}

&__history-paging-sentinel {
width: 100%;
height: 28px;
min-height: 28px;
display: flex;
align-items: center;
justify-content: center;
gap: 6px;
color: var(--color-text-muted);
font-size: 12px;
line-height: 18px;
pointer-events: none;
overflow-anchor: none;
visibility: hidden;

&[data-history-paging-sentinel='loading'] {
visibility: visible;
}
}

&__history-paging-spinner {
animation: history-paging-spin 0.9s linear infinite;
}

.message-list-footer {
/* Inline height from VirtualMessageList (measured drop-zone + bottom inset + tail clearance). */
Expand Down Expand Up @@ -150,3 +174,8 @@
}

}

@keyframes history-paging-spin {
from { transform: rotate(0deg); }
to { transform: rotate(360deg); }
}
126 changes: 126 additions & 0 deletions src/web-ui/src/flow_chat/components/modern/VirtualMessageList.session-boundary.test.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -197,6 +197,9 @@ vi.mock('../../store/chatInputStateStore', () => ({

vi.mock('../../store/FlowChatStore', () => ({
flowChatStore: {
getState: () => ({
sessions: new Map(stateMocks.activeSession ? [[stateMocks.activeSession.sessionId, stateMocks.activeSession]] : []),
}),
hasPendingSessionHistoryCompletion: flowStoreMocks.hasPendingSessionHistoryCompletion,
hasDeferredSessionHistoryProjection: flowStoreMocks.hasDeferredSessionHistoryProjection,
requestSessionFullHistoryProjection: flowStoreMocks.requestSessionFullHistoryProjection,
Expand Down Expand Up @@ -2153,6 +2156,129 @@ describe('VirtualMessageList session boundary', () => {
expect(flowStoreMocks.revealPreviousSessionHistoryWindow).toHaveBeenCalledWith('session-a', 'wheel-up');
});

it('expands partial static history before prepending older turns', () => {
flowStoreMocks.hasDeferredSessionHistoryProjection.mockReturnValue(true);
flowStoreMocks.revealPreviousSessionHistoryWindow.mockReturnValue(true);
stateMocks.activeSession = createSessionWithTurns('session-a', ['turn-3', 'turn-4', 'turn-5'], {
isHistorical: true,
historyState: 'ready',
contextRestoreState: 'pending',
isPartial: true,
loadedTurnCount: 3,
totalTurnCount: 6,
});
stateMocks.virtualItems = ['turn-3', 'turn-4', 'turn-5'].flatMap(turnId => [
createItem(turnId),
createModelItem(turnId),
]);

act(() => {
root.render(<VirtualMessageList />);
});

const staticScroller = container.querySelector<HTMLElement>('[data-virtuoso-scroller="true"]');
expect(staticScroller).not.toBeNull();
expect(container.querySelector('[data-initial-history-render-windowed]')).not.toBeNull();

act(() => {
staticScroller?.dispatchEvent(new WheelEvent('wheel', {
deltaY: -120,
bubbles: true,
}));
});

expect(container.querySelector('[data-initial-history-render-windowed]')).not.toBeNull();
expect(container.querySelector('[data-testid="virtuoso"]')).toBeNull();
expect(container.querySelector('[data-history-initial-render-spacer="true"]')).toBeNull();
expect(container.querySelector('[data-turn-id="turn-3"]')).not.toBeNull();
expect(container.querySelector('[data-history-paging-sentinel="loading"]')).not.toBeNull();
expect(flowStoreMocks.revealPreviousSessionHistoryWindow).not.toHaveBeenCalled();

flushAnimationFrame();
flushAnimationFrame();

expect(flowStoreMocks.revealPreviousSessionHistoryWindow).toHaveBeenCalledWith('session-a', 'wheel-up');

stateMocks.activeSession = createSessionWithTurns(
'session-a',
['turn-0', 'turn-1', 'turn-2', 'turn-3', 'turn-4', 'turn-5'],
{
isHistorical: true,
historyState: 'ready',
contextRestoreState: 'pending',
isPartial: false,
loadedTurnCount: 6,
totalTurnCount: 6,
},
);
stateMocks.virtualItems = ['turn-0', 'turn-1', 'turn-2', 'turn-3', 'turn-4', 'turn-5'].flatMap(turnId => [
createItem(turnId),
createModelItem(turnId),
]);

act(() => {
root.render(<VirtualMessageList />);
});

expect(container.querySelector('[data-history-initial-render-spacer="true"]')).toBeNull();
expect(container.querySelector('[data-turn-id="turn-3"]')).not.toBeNull();
expect(container.querySelector('[data-history-paging-sentinel]')).toBeNull();
});

it('waits until the static history boundary is near before starting pagination', () => {
flowStoreMocks.hasDeferredSessionHistoryProjection.mockReturnValue(true);
stateMocks.activeSession = createSessionWithTurns('session-a', ['turn-3', 'turn-4', 'turn-5'], {
isHistorical: true,
historyState: 'ready',
contextRestoreState: 'pending',
isPartial: true,
loadedTurnCount: 3,
totalTurnCount: 6,
});
stateMocks.virtualItems = ['turn-3', 'turn-4', 'turn-5'].flatMap(turnId => [
createItem(turnId),
createModelItem(turnId),
]);

act(() => {
root.render(<VirtualMessageList />);
});

const scroller = container.querySelector<HTMLElement>('[data-virtuoso-scroller="true"]');
const spacer = container.querySelector<HTMLElement>('[data-history-initial-render-spacer="true"]');
expect(scroller).not.toBeNull();
expect(spacer).not.toBeNull();
if (!scroller || !spacer) {
return;
}

const spacerHeight = Number.parseFloat(spacer.style.height);
setScrollerGeometry(scroller, {
scrollHeight: spacerHeight + 3_000,
clientHeight: 1_000,
scrollTop: spacerHeight + 500,
});

act(() => {
scroller.dispatchEvent(new WheelEvent('wheel', { deltaY: -120, bubbles: true }));
scroller.dispatchEvent(new Event('scroll', { bubbles: true }));
});
flushAnimationFrame();
flushAnimationFrame();

expect(container.querySelector('[data-initial-history-render-windowed]')).not.toBeNull();
expect(flowStoreMocks.revealPreviousSessionHistoryWindow).not.toHaveBeenCalled();

scroller.scrollTop = spacerHeight + 100;
act(() => {
scroller.dispatchEvent(new Event('scroll', { bubbles: true }));
});

expect(container.querySelector('[data-initial-history-render-windowed]')).not.toBeNull();
expect(container.querySelector('[data-history-initial-render-spacer="true"]')).toBeNull();
expect(container.querySelector('[data-history-paging-sentinel="loading"]')).not.toBeNull();
});

it('does not reveal previous history for upward scroll away from the history boundary', () => {
flowStoreMocks.hasDeferredSessionHistoryProjection.mockReturnValue(true);
stateMocks.activeSession = createSession('session-a', 'turn-a', {
Expand Down
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