diff --git a/openspec/changes/code-review-fix/tasks.md b/openspec/changes/code-review-fix/tasks.md
index ba9a79d..ec2d8e6 100644
--- a/openspec/changes/code-review-fix/tasks.md
+++ b/openspec/changes/code-review-fix/tasks.md
@@ -36,7 +36,7 @@
 - [x] 4.8 `[sonnet]` Wrap chart cascade delete in `db.transaction()` and add `spanAnnotations` deletion in `src/app/api/charts/[id]/route.ts`
 - [x] 4.9 `[haiku]` Add `parseInt(value, 10)` with `isNaN()` guard to all routes parsing integer query params
 - [x] 4.10 `[sonnet]` Add CSV injection protection (prefix `=+@-` cells with `'`) to all export routes
-- [ ] 4.11 `[sonnet]` Add `response.ok` checks before `.json()` in `src/app/page.tsx` (lines 214, 230, 245, 257)
+- [x] 4.11 `[sonnet]` Add `response.ok` checks before `.json()` in `src/app/page.tsx` (lines 214, 230, 245, 257)
 - [ ] 4.12 `[sonnet]` Add `response.ok` checks before `.json()` in `src/components/CandleChart.tsx` (lines 163, 178, 192)
 
 ## 5. ML Service Hardening (Python)
diff --git a/src/app/page.tsx b/src/app/page.tsx
index 6ea49c1..87e8f2c 100644
--- a/src/app/page.tsx
+++ b/src/app/page.tsx
@@ -211,6 +211,7 @@ export default function Home() {
   const fetchCharts = useCallback(async () => {
     try {
       const response = await fetch('/api/charts');
+      if (!response.ok) throw new Error(`HTTP error! status: ${response.status}`);
       const data = await response.json();
       setCharts(data);
       return data as Chart[];
@@ -228,6 +229,7 @@ export default function Home() {
     }
     try {
       const response = await fetch(`/api/annotations?chartId=${chartId}`);
+      if (!response.ok) throw new Error(`HTTP error! status: ${response.status}`);
       const data = await response.json();
       setAnnotations(data);
     } catch (error) {
@@ -243,6 +245,7 @@ export default function Home() {
     }
     try {
       const response = await fetch(`/api/span-annotations?chartId=${chartId}`);
+      if (!response.ok) throw new Error(`HTTP error! status: ${response.status}`);
       const data = await response.json();
       setSpanAnnotations(data);
     } catch (error) {
@@ -254,6 +257,7 @@ export default function Home() {
   const fetchSpanLabelTypes = useCallback(async () => {
     try {
       const response = await fetch('/api/span-label-types');
+      if (!response.ok) throw new Error(`HTTP error! status: ${response.status}`);
       const data = await response.json();
       setSpanLabelTypes(data);
     } catch (error) {