diff --git a/.jules/bolt.md b/.jules/bolt.md
index d81fd70a..3d330d41 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -17,3 +17,13 @@
 
 **Learning:** When attempting to optimize an O(N^2) array spread operation (`[...existing, talk]`) inside a grouping loop in `groupTalksByTrack`, the purely functional/immutable constraint specified by the team (and the lack of `Map.groupBy` support in Node 20.x Jest environments) means that we must fall back to immutable reductions.
 **Action:** When constraints require strict immutability without mutation of objects, use `reduce` with object and array spreads (e.g., `{ ...acc, [key]: [...(acc[key] || []), item] }`) even if it introduces O(N^2) overhead for large arrays. Avoid using `push()` or modifying accumulators directly. Always run Prettier/formatting checks before merge to resolve CI failures.
+
+## 2026-05-03 - Array filtering with repeated includes()
+
+**Learning:** Found an O(N\*M) performance bottleneck in `ScheduleContainer.tsx` where `Array.includes()` was being called inside a function on every re-render or schedule update.
+**Action:** Convert the lookup array into a `Set` outside the iteration loop and use `Set.has()` to achieve O(N+M) time complexity. Ensure this pattern is verified during profiling.
+
+## 2026-03-24 - Array filtering with repeated includes()
+
+**Learning:** Found an O(N\*M) performance bottleneck in `ScheduleContainer.tsx` where `Array.includes()` was being called inside a `.filter()` function on every re-render or schedule update.
+**Action:** Convert the lookup array into a `Set` outside the iteration loop and use `Set.has()` to achieve O(N+M) time complexity. Ensure this pattern is verified during profiling.
diff --git a/components/schedule/ScheduleContainer.tsx b/components/schedule/ScheduleContainer.tsx
index 33d877a4..92eaa72d 100644
--- a/components/schedule/ScheduleContainer.tsx
+++ b/components/schedule/ScheduleContainer.tsx
@@ -20,7 +20,9 @@ export default function ScheduleContainer({ initialSchedule, year }: Readonly<Sc
       return initialSchedule;
     }
 
-    const filterSessions = (sessions: GridSession[]) => sessions.filter((s) => savedSessionIds.includes(s.id) || s.isServiceSession);
+    const savedSessionsSet = new Set(savedSessionIds);
+
+    const filterSessions = (sessions: GridSession[]) => sessions.filter((s) => savedSessionsSet.has(s.id) || s.isServiceSession);
 
     return initialSchedule.map((day) => ({
       ...day,