diff --git a/webviews/src/agent-session/acpmux/App.tsx b/webviews/src/agent-session/acpmux/App.tsx
index 18583faf2d17..dd833f48f894 100644
--- a/webviews/src/agent-session/acpmux/App.tsx
+++ b/webviews/src/agent-session/acpmux/App.tsx
@@ -1981,13 +1981,16 @@ export function VirtualTranscript({
   let lastTurnId: string | undefined;
   for (let index = rows.length - 1; index >= 0 && !lastTurnId; index -= 1)
     if (rows[index]!.kind === "turnSummary") lastTurnId = rows[index]!.id;
-  const markTurns = () => {
+  const markTurns = useCallback(() => {
     for (const node of thread.current?.querySelectorAll<HTMLElement>(".acpmux-row") ?? []) {
       node.toggleAttribute("data-last-turn", node.dataset.rowId === lastTurnId);
       node.toggleAttribute("data-turn-revealed", node.dataset.rowId === pointedTurn.current);
     }
-  };
-  useLayoutEffect(markTurns);
+  }, [lastTurnId]);
+  // Mark only when the mounted rows, their range, or the last turn changes. The old no-deps
+  // layout effect scanned every commit, including scroll/follow state commits that cannot change
+  // these attributes. `pointAt` still calls the callback directly for pointer-driven updates.
+  useLayoutEffect(markTurns, [markTurns, rows, range.first, range.last]);
   // Older history pages in before the reader reaches it: whenever the view is within two viewports
   // of the first loaded row, including a tail too short to fill them. The anchoring above keeps the
   // reader's row in place as each page lands.