frontend/src/hooks/useKoreaData.ts

@@ -145,15 +145,24 @@ export function useKoreaData({
   // Propagate Korea aircraft (live only — no waypoint propagation needed)
   const aircraft = useMemo(() => propagateAircraft(baseAircraftKorea, currentTime), [baseAircraftKorea, currentTime]);
 
-  // Korea region ships — pre-compute mtCategory/natGroup for O(1) filter lookups
-  const ships = useMemo(() => {
-    const propagated = propagateShips(baseShipsKorea, currentTime, isLive);
-    for (const s of propagated) {
-      s.mtCategory = getMarineTrafficCategory(s.typecode, s.category);
-      s.natGroup = getNationalityGroup(s.flag);
-    }
-    return propagated;
-  }, [baseShipsKorea, currentTime, isLive]);
+  // Pre-compute mtCategory/natGroup on base data change (5-min polling)
+  // useState 값 직접 변경 불가 → 새 배열을 ref에 저장
+  const enrichedShipsRef = useRef<Ship[]>([]);
+  useMemo(() => {
+    enrichedShipsRef.current = baseShipsKorea.map(s => ({
+      ...s,
+      mtCategory: getMarineTrafficCategory(s.typecode, s.category),
+      natGroup: getNationalityGroup(s.flag),
+    }));
+  }, [baseShipsKorea]);
+
+  // Korea region ships
+  // LIVE: enrichedShipsRef 동일 참조 반환 → 하위 useMemo 재실행 방지 (매초 currentTime 변경 무시)
+  // REPLAY: propagateShips로 위치 보간 → 새 배열 반환 (mtCategory는 spread로 상속)
+  const ships = useMemo(
+    () => isLive ? enrichedShipsRef.current : propagateShips(enrichedShipsRef.current, currentTime, false),
+    [baseShipsKorea, currentTime, isLive],
+  );
 
   // Category-filtered data for map rendering (Set.has = O(1) per ship)
   const visibleAircraft = useMemo(