⚡ Bolt: Memoize displayList in ProjetsTab

.jules/bolt.md

@@ -21,3 +21,7 @@
 ## 2024-07-10 - O(n) Single Pass Data Aggregation
 **Learning:** Using chained array methods (e.g. `.map().filter()`, `.flatMap()`, and repeated `.filter()` over the same large list like `profiles`) leads to redundant O(n) passes over data and allocates unnecessary intermediate arrays. This blocks the main thread longer than necessary when calculating basic statistics like `uniqueCities`, `uniqueTechs`, or total counts.
 **Action:** Consolidate statistical aggregations over large object arrays into a single O(n) `for` loop that updates multiple accumulators (like `Set` objects and primitive counters) in one pass, thereby improving performance and reducing memory overhead.
+
+## 2024-07-18 - Component Map Memoization Pattern
+**Learning:** In React components with highly interactive state (like buttons triggering local state changes such as `visibleCount`), mapping over raw datasets to create derived UI objects outside of a `useMemo` block leads to unnecessary O(N) object allocations and garbage collection on every render.
+**Action:** When a component derives lists from props or state for rendering, wrap the mapping or filtering logic inside `useMemo` to cache the result, recalculating only when the underlying data changes, thereby freeing up the main thread from redundant object allocations.

src/pages/matching-page.tsx

@@ -508,12 +508,17 @@ function ProjetsTab({
     }
   }, [user, interested]);
 
-  const displayList: { project: Project; score?: number; reasons?: string[] }[] =
-    profile && projectMatches.length > 0
+  // ⚡ Bolt: Memoize the mapping logic to prevent O(N) object allocations on every render
+  // This avoids redundant work when local interactive states (like visibleCount or interested) change.
+  // Impact: Reduces main-thread blocking during re-renders by caching derived datasets.
+  const displayList: { project: Project; score?: number; reasons?: string[] }[] = useMemo(() => {
+    return profile && projectMatches.length > 0
       ? projectMatches.map((m) => ({ project: m.project, score: m.score, reasons: m.reasons }))
       : projects.map((p) => ({ project: p }));
+  }, [profile, projectMatches, projects]);
 
-  const visible = displayList.slice(0, visibleCount);
+  // ⚡ Bolt: Memoize slicing to prevent re-instantiating the visible array on unrelated renders.
+  const visible = useMemo(() => displayList.slice(0, visibleCount), [displayList, visibleCount]);
 
   if (isLoading) {
     return (