fix: duplicate segmentation entries on layout switch (#5458)

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

BUG_FIX_SUMMARY.md

@@ -0,0 +1,92 @@
+# Bug Fix: Duplicate Segmentation Entries When Switching Layouts
+
+## Issue Description
+**Linear Issue:** OHI-2076  
+**Title:** [Bug] Duplicate entries for same segmentation when switching between Common and advanced layout
+
+When switching from a Common layout to an advanced layout (e.g., 3D Four-Up) in the OHIF Viewer, duplicate entries for the same segmentation appear in the Segmentation Panel.
+
+## Root Cause
+The issue was in the `useViewportSegmentations` hook located at:
+```
+extensions/cornerstone/src/hooks/useViewportSegmentations.ts
+```
+
+When a viewport contains multiple representations of the same segmentation (e.g., both a LABELMAP and SURFACE representation), the hook was creating separate entries for each representation, even though they belong to the same segmentation. This resulted in duplicate entries in the Segmentation Panel.
+
+The problem occurred because:
+1. When switching layouts, new viewports are created
+2. The synchronizer may add the same segmentation with different representation types to these viewports
+3. The `getSegmentationRepresentations(viewportId)` call returns ALL representations for that viewport
+4. Each representation was mapped to a separate entry, creating duplicates
+
+## Solution
+Added deduplication logic in the `useViewportSegmentations` hook to ensure only one entry per unique `segmentationId` is shown in the panel, regardless of how many representation types exist.
+
+### Code Changes
+
+**File:** `extensions/cornerstone/src/hooks/useViewportSegmentations.ts`
+
+**Before:**
+```typescript
+const representations = segmentationService.getSegmentationRepresentations(viewportId);
+
+const newSegmentationsWithRepresentations = representations.map(representation => {
+  const segmentation = segmentationService.getSegmentation(representation.segmentationId);
+  const mappedSegmentation = mapSegmentationToDisplay(segmentation, customizationService);
+  return {
+    representation,
+    segmentation: mappedSegmentation,
+  };
+});
+```
+
+**After:**
+```typescript
+const representations = segmentationService.getSegmentationRepresentations(viewportId);
+
+// Deduplicate representations by segmentationId to prevent showing
+// the same segmentation multiple times in the panel when it has
+// multiple representation types (e.g., labelmap and surface)
+const uniqueSegmentationMap = new Map();
+representations.forEach(representation => {
+  if (!uniqueSegmentationMap.has(representation.segmentationId)) {
+    uniqueSegmentationMap.set(representation.segmentationId, representation);
+  }
+});
+
+const newSegmentationsWithRepresentations = Array.from(uniqueSegmentationMap.values()).map(
+  representation => {
+    const segmentation = segmentationService.getSegmentation(representation.segmentationId);
+    const mappedSegmentation = mapSegmentationToDisplay(segmentation, customizationService);
+    return {
+      representation,
+      segmentation: mappedSegmentation,
+    };
+  }
+);
+```
+
+## How It Works
+1. After retrieving all representations for a viewport, we create a `Map` keyed by `segmentationId`
+2. We iterate through all representations and only add the first occurrence of each unique `segmentationId`
+3. This ensures that even if a segmentation has multiple representation types (labelmap, surface, etc.), only one entry appears in the panel
+4. The fix is applied at the data source level, ensuring consistency across all panel views
+
+## Testing
+To verify the fix:
+1. Launch OHIF Viewer with segmentation data (e.g., https://viewer-dev.ohif.org/segmentation?StudyInstanceUIDs=1.3.6.1.4.1.14519.5.2.1.1706.8374.643249677828306008300337414785)
+2. Drag and drop a segmentation into the Common layout viewport
+3. Switch to an advanced layout (e.g., 3D Four-Up)
+4. Verify that only one entry per segmentation appears in the Segmentation Panel (no duplicates)
+
+## Impact
+- **Scope:** Minimal - only affects the display logic in the Segmentation Panel
+- **Breaking Changes:** None
+- **Performance:** Negligible - adds a simple Map-based deduplication step
+- **User Experience:** Significantly improved - eliminates confusion from duplicate entries
+
+## Related Files
+- `/workspace/extensions/cornerstone/src/hooks/useViewportSegmentations.ts` (modified)
+- `/workspace/extensions/cornerstone/src/hooks/useActiveViewportSegmentationRepresentations.ts` (uses the fixed hook)
+- `/workspace/extensions/cornerstone/src/panels/PanelSegmentation.tsx` (consumes the data)

extensions/cornerstone/src/hooks/useViewportSegmentations.ts

@@ -152,15 +152,27 @@ export function useViewportSegmentations({
 
       const representations = segmentationService.getSegmentationRepresentations(viewportId);
 
-      const newSegmentationsWithRepresentations = representations.map(representation => {
-        const segmentation = segmentationService.getSegmentation(representation.segmentationId);
-        const mappedSegmentation = mapSegmentationToDisplay(segmentation, customizationService);
-        return {
-          representation,
-          segmentation: mappedSegmentation,
-        };
+      // Deduplicate representations by segmentationId to prevent showing
+      // the same segmentation multiple times in the panel when it has
+      // multiple representation types (e.g., labelmap and surface)
+      const uniqueSegmentationMap = new Map();
+      representations.forEach(representation => {
+        if (!uniqueSegmentationMap.has(representation.segmentationId)) {
+          uniqueSegmentationMap.set(representation.segmentationId, representation);
+        }
       });
 
+      const newSegmentationsWithRepresentations = Array.from(uniqueSegmentationMap.values()).map(
+        representation => {
+          const segmentation = segmentationService.getSegmentation(representation.segmentationId);
+          const mappedSegmentation = mapSegmentationToDisplay(segmentation, customizationService);
+          return {
+            representation,
+            segmentation: mappedSegmentation,
+          };
+        }
+      );
+
       setSegmentationsWithRepresentations({
         segmentationsWithRepresentations: newSegmentationsWithRepresentations,
         disabled: false,