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fix(flow-chat): stop follow output jitter #648

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Merged
bobleer merged 1 commit into from
May 11, 2026
Merged

fix(flow-chat): stop follow output jitter #648

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62 changes: 3 additions & 59 deletions src/web-ui/src/flow_chat/components/modern/VirtualMessageList.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -1591,58 +1591,8 @@ export const VirtualMessageList = forwardRef<VirtualMessageListRef>((_, ref) =>
}, [userMessageItems]);

const performAutoFollowSync = useCallback(() => {
if (!latestTurnId) {
return;
}

const currentPinReservation = bottomReservationStateRef.current.pin;
const totalBottomCompensationPx = getTotalBottomCompensationPx();
const hasPendingLatestStickyPin = (
pendingTurnPin?.turnId === latestTurnId &&
pendingTurnPin.pinMode === 'sticky-latest'
);
const hasAppliedLatestStickyPin = (
currentPinReservation.mode === 'sticky-latest' &&
currentPinReservation.targetTurnId === latestTurnId
);
const shouldKeepStickyLatest = (
hasAppliedLatestStickyPin &&
currentPinReservation.floorPx > COMPENSATION_EPSILON_PX
);
const shouldPreserveSyntheticTail = (
hasAppliedLatestStickyPin &&
totalBottomCompensationPx > COMPENSATION_EPSILON_PX
);

if (hasPendingLatestStickyPin) {
return;
}

if (!hasAppliedLatestStickyPin) {
requestTurnPinToTop(latestTurnId, {
behavior: 'auto',
pinMode: 'sticky-latest',
});
return;
}

if (shouldKeepStickyLatest) {
return;
}

if (shouldPreserveSyntheticTail) {
return;
}

scrollToLatestEndPositionInternal('auto');
}, [
getTotalBottomCompensationPx,
latestTurnId,
pendingTurnPin?.pinMode,
pendingTurnPin?.turnId,
requestTurnPinToTop,
scrollToLatestEndPositionInternal,
]);
}, [scrollToLatestEndPositionInternal]);

const {
isFollowingOutput,
Expand Down Expand Up @@ -1674,15 +1624,9 @@ export const VirtualMessageList = forwardRef<VirtualMessageListRef>((_, ref) =>
},
shouldSuspendAutoFollow,
getAutoFollowDistanceFromBottom: (scroller) => (
Math.max(0, scroller.scrollHeight - scroller.clientHeight - scroller.scrollTop - getTotalBottomCompensationPx())
Math.max(0, scroller.scrollHeight - scroller.clientHeight - scroller.scrollTop)
),
onContinuousFollowFrame: () => {
// Keep sticky-latest pin floor aligned with the live DOM as collapses
// shrink the layout. Without this the pin reservation would lag for one
// RAF tick and the viewport would briefly land below the latest user
// message.
reconcileStickyPinReservation();
},
onContinuousFollowFrame: undefined,
});

useEffect(() => {
Expand Down
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