feat: [performance improvement] Optimize saved session lookups in ScheduleContainer

.jules/bolt.md

@@ -1,4 +1,8 @@
 ## 2024-05-18 - Avoid array spreads inside loops for Map grouping
 
 **Learning:** In Next.js/React applications, when grouping items (like schedules or talks) into a `Map` where the values are arrays, using the array spread operator `[...existing, item]` inside a loop (like `forEach` or `map`) causes amortized O(N^2) memory allocations and unnecessary Garbage Collection overhead.
-**Action:** Always use `.push()` on the existing array reference if the data structure permits local mutation. For strict ESLint configurations enforcing `no-restricted-syntax`, extract the existing array, push to it, and handle the fallback elegantly (`if (!existing) { map.set(key, [item]); } else { existing.push(item); }`).
+
+## 2024-05-25 - Avoid array includes inside array filter operations
+
+**Learning:** In Next.js/React applications, when filtering a list of items based on their presence in another array (e.g., `savedSessionIds.includes(s.id)` inside a `filter` function), it leads to an O(N \* M) time complexity. This can cause performance bottlenecks and block the main thread, especially if the arrays are large.
+**Action:** Convert the lookup array into a `Set` before the filtering loop. Use `set.has(id)` inside the `filter` function to achieve O(N + M) time complexity.

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 savedIdsSet = new Set(savedSessionIds);
+
+    const filterSessions = (sessions: GridSession[]) => sessions.filter((s) => savedIdsSet.has(s.id) || s.isServiceSession);
 
     return initialSchedule.map((day) => ({
       ...day,