diff --git a/openspec/changes/code-review-fix/tasks.md b/openspec/changes/code-review-fix/tasks.md
index ec2d8e6..950ed97 100644
--- a/openspec/changes/code-review-fix/tasks.md
+++ b/openspec/changes/code-review-fix/tasks.md
@@ -37,7 +37,7 @@
 - [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
 - [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)
+- [x] 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/components/CandleChart.tsx b/src/components/CandleChart.tsx
index cb6a8c3..ba3336b 100644
--- a/src/components/CandleChart.tsx
+++ b/src/components/CandleChart.tsx
@@ -161,6 +161,7 @@ const CandleChart = forwardRef<CandleChartHandle, CandleChartProps>(
       try {
         const url = activeChartId ? `/api/candles?chartId=${activeChartId}` : '/api/candles';
         const response = await fetch(url);
+        if (!response.ok) throw new Error(`HTTP error! status: ${response.status}`);
         const data = await response.json();
         setCandles(data);
         setIsEmpty(data.length === 0);
@@ -176,6 +177,7 @@ const CandleChart = forwardRef<CandleChartHandle, CandleChartProps>(
       try {
         const url = activeChartId ? `/api/annotations?chartId=${activeChartId}` : '/api/annotations';
         const response = await fetch(url);
+        if (!response.ok) throw new Error(`HTTP error! status: ${response.status}`);
         const data = await response.json();
         setAnnotations(data);
         return data;
@@ -189,6 +191,7 @@ const CandleChart = forwardRef<CandleChartHandle, CandleChartProps>(
     const fetchAnnotationTypes = async () => {
       try {
         const response = await fetch('/api/annotation-types');
+        if (!response.ok) throw new Error(`HTTP error! status: ${response.status}`);
         const data = await response.json();
         setAnnotationTypes(data.filter((t: AnnotationType) => t.is_active));
         return data;