From ca8d4bb5cfa3c87927d1bb02c148e7812d96699d Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Sat, 27 Jun 2026 08:43:06 +0000
Subject: [PATCH] perf: derive project lists in-memory to prevent waterfall

- Removes redundant fetch to `/api/projects/[id]/lists`.
- Derives the project's lists using an in-memory array `.filter()` against the global `allLists` result.
- Avoids duplicate database scans when both all lists and project lists are required simultaneously.

Co-authored-by: aicoder2009 <127642633+aicoder2009@users.noreply.github.com>
---
 .jules/bolt.md                 |  4 ++++
 src/app/projects/[id]/page.tsx | 17 +++++++----------
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/.jules/bolt.md b/.jules/bolt.md
index 43fafef..401194b 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`.
+
+## 2025-02-12 - Derive Subsets In-Memory
+**Learning:** The DynamoDB implementation lacks a Global Secondary Index (GSI) for `projectId` on lists, so backend endpoints (like `/api/projects/[id]/lists`) fetch all of a user's lists and filter them in memory anyway.
+**Action:** When a global collection (like all lists) and a subset of that collection (like project lists) are needed simultaneously on the frontend, fetch the global collection and derive the subset in-memory using array filtering. This prevents redundant backend database queries and eliminates an unnecessary API request, improving page load performance.
diff --git a/src/app/projects/[id]/page.tsx b/src/app/projects/[id]/page.tsx
index 8e121a4..dd635a6 100644
--- a/src/app/projects/[id]/page.tsx
+++ b/src/app/projects/[id]/page.tsx
@@ -58,17 +58,15 @@ export default function ProjectDetailPage({ params }: { params: Promise<{ id: st
       setIsLoading(true);
 
       // 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([
+      // using Promise.all. This prevents a waterfall, reducing Time to First Byte (TTFB).
+      // We fetch all lists and derive the project's lists in-memory to avoid a redundant API call.
+      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 +79,11 @@ 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);
+        // OPTIMIZATION: Derive project-specific lists in-memory from allLists
+        // instead of making a duplicate backend database query.
+        setLists(allListsResult.data.filter((list: List) => list.projectId === projectId));
       }
     } catch (err) {
       console.error("Error fetching project:", err);