diff --git a/openspec/changes/code-review-fix/tasks.md b/openspec/changes/code-review-fix/tasks.md
index e48de15..0947a31 100644
--- a/openspec/changes/code-review-fix/tasks.md
+++ b/openspec/changes/code-review-fix/tasks.md
@@ -73,7 +73,7 @@
 - [x] 8.1 `[opus]` Fix SpanAnnotationManager preview primitive memory leak: replace `useState` with `useRef` for preview primitive, add cleanup on unmount (`src/components/SpanAnnotationManager.tsx:265-324`)
 - [x] 8.2 `[sonnet]` Use `chart.applyOptions()` for theme changes instead of re-creating chart (`src/components/CandleChart.tsx:333`)
 - [x] 8.3 `[sonnet]` Remove `fitContent()` from reconciliation effect, only call on initial load (`src/components/SpanAnnotationManager.tsx:160`)
-- [ ] 8.4 `[opus]` Implement incremental primitive updates in SpanAnnotationManager: update only selection state on selection change, full reconciliation only on annotation list changes (`src/components/SpanAnnotationManager.tsx:104-161`)
+- [x] 8.4 `[opus]` Implement incremental primitive updates in SpanAnnotationManager: update only selection state on selection change, full reconciliation only on annotation list changes (`src/components/SpanAnnotationManager.tsx:104-161`)
 - [ ] 8.5 `[sonnet]` Add bounded prediction cache (max 100 entries, FIFO eviction) to `predictionCacheRef` (`src/app/page.tsx:195-199`)
 - [ ] 8.6 `[sonnet]` Fix hardcoded 1-minute candle interval: detect interval from data, use for span iteration (`src/components/CandleChart.tsx:452`)
 - [ ] 8.7 `[haiku]` Extract magic numbers (8px, 60s, colors) to named constants in `CandleChart.tsx`
diff --git a/src/components/SpanAnnotationManager.tsx b/src/components/SpanAnnotationManager.tsx
index 1fa0e0f..8f559bc 100644
--- a/src/components/SpanAnnotationManager.tsx
+++ b/src/components/SpanAnnotationManager.tsx
@@ -121,7 +121,7 @@ export default function SpanAnnotationManager({
     return { max_high, min_low };
   };
 
-  // Render span annotations as primitives
+  // Full reconciliation: rebuild all primitives when annotation list changes
   useEffect(() => {
     if (!series || !chart) return;
 
@@ -170,13 +170,20 @@ export default function SpanAnnotationManager({
 
       const primitive = new SpanRectanglePrimitive({
         data: spanData,
-        isSelected: span.id === selectedSpanId,
+        isSelected: span.id === selectedSpanIdRef.current,
       });
 
       series.attachPrimitive(primitive);
       primitivesRef.current.set(span.id, primitive);
     });
-  }, [spanAnnotations, selectedSpanId, series, chart, candles]);
+  }, [spanAnnotations, series, chart, candles]);
+
+  // Selection-only effect: update visual state without rebuilding primitives
+  useEffect(() => {
+    primitivesRef.current.forEach((primitive, spanId) => {
+      primitive.setSelected(spanId === selectedSpanId);
+    });
+  }, [selectedSpanId]);
 
   // Fit chart content only on initial load when chart and series become available
   useEffect(() => {