diff --git a/.jules/bolt.md b/.jules/bolt.md
index 43fafef..db9bb03 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -5,3 +5,7 @@
 ## 2024-05-18 - Concurrent Fetching with Owner IDs in Share Links
 **Learning:** In the share system, endpoints processing a share code typically suffer from waterfall latency by first loading target entity details (like a project) and then querying its associated elements (like project lists) using the entity's owner ID (`userId`). However, the `shareLink` object already contains the `userId` field (representing the owner's ID).
 **Action:** Always leverage the existing owner's ID within `shareLink` to bypass sequential dependencies and fetch parent entities (like projects) concurrently with their child elements (like user lists) using `Promise.all`.
+
+## 2024-11-20 - Frontend In-Memory Filtering for DynamoDB Subsets
+**Learning:** The DynamoDB implementation lacks a Global Secondary Index (GSI) for `projectId` on lists. Thus, the `/api/projects/[id]/lists` backend route just fetches all user lists via `getUserLists` and filters them anyway. On pages that need both "all lists" and "project lists" (like `src/app/projects/[id]/page.tsx`), fetching both via API results in duplicate full-table scans.
+**Action:** When fetching a global collection (e.g., all lists) and a subset of that collection (e.g., project lists) simultaneously on the frontend, derive the subset in-memory using array filtering instead of making a redundant API request to avoid duplicate backend database queries.
diff --git a/src/app/projects/[id]/page.tsx b/src/app/projects/[id]/page.tsx
index 8e121a4..e077b11 100644
--- a/src/app/projects/[id]/page.tsx
+++ b/src/app/projects/[id]/page.tsx
@@ -60,15 +60,16 @@ export default function ProjectDetailPage({ params }: { params: Promise<{ id: st
       // OPTIMIZATION: Execute independent network requests and JSON parsing concurrently
       // using Promise.all. This prevents a 3-step waterfall, reducing Time to First Byte
       // (TTFB) and overall load time significantly on this detail page.
-      const [projectRes, listsRes, allListsRes] = await Promise.all([
+      // Additionally, we derive the project's lists in-memory by filtering `allListsResult`
+      // instead of making a redundant API request to `/api/projects/${projectId}/lists`,
+      // which avoids a duplicate backend database query.
+      const [projectRes, allListsRes] = await Promise.all([
         fetch(`/api/projects/${projectId}`),
-        fetch(`/api/projects/${projectId}/lists`),
         fetch("/api/lists"),
       ]);
 
-      const [projectResult, listsResult, allListsResult] = await Promise.all([
+      const [projectResult, allListsResult] = await Promise.all([
         projectRes.json(),
-        listsRes.json(),
         allListsRes.json(),
       ]);
 
@@ -81,12 +82,9 @@ export default function ProjectDetailPage({ params }: { params: Promise<{ id: st
       setEditName(projectResult.data.name);
       setEditDescription(projectResult.data.description || "");
 
-      if (listsResult.success) {
-        setLists(listsResult.data);
-      }
-
       if (allListsResult.success) {
         setAllLists(allListsResult.data);
+        setLists(allListsResult.data.filter((list: List) => list.projectId === projectId));
       }
     } catch (err) {
       console.error("Error fetching project:", err);