fix: minor updated the region lasso selection behavior

src/components/MainContent.tsx

@@ -94,6 +94,7 @@ const MainContent: React.FC<MainContentProps> = ({
 
   // Refs to track pending updates for verification
   const pendingUpdates = useRef<Map<string, { trackId: string, regionId: string, startBeat: number, length: number }>>(new Map());
+  const preventEmptyMainContentDeselectRef = useRef(false);
 
   // Refs for auto-scroll during playback
   const mainContentRef = useRef<HTMLDivElement | null>(null);
@@ -632,9 +633,18 @@ const MainContent: React.FC<MainContentProps> = ({
       return;
     }
 
+    if (preventEmptyMainContentDeselectRef.current) {
+      preventEmptyMainContentDeselectRef.current = false;
+      return;
+    }
+
     handleRegionLassoSelection([], { shiftKey: false });
   };
 
+  const handleRegionLassoCommit = () => {
+    preventEmptyMainContentDeselectRef.current = true;
+  };
+
   // Handle region single click: selection only (no piano roll opening)
   const handleRegionClick = (regionId: string, options: RegionClickOptions = { shiftKey: false }) => {
     if (DEBUG_MODE.MAIN_CONTENT) {
@@ -990,6 +1000,7 @@ const MainContent: React.FC<MainContentProps> = ({
             onRegionUpdated={handleRegionUpdated}
             onRegionClick={handleRegionClick}
             onRegionLassoSelection={handleRegionLassoSelection}
+            onRegionLassoCommit={handleRegionLassoCommit}
             onOpenPianoRoll={handleOpenPianoRoll}
             onOpenSpectrogram={handleOpenSpectrogram}
             showHybridButtonForAudio={showHybridButtonForAudio}

src/components/track/TrackGridPanel.test.tsx

@@ -119,6 +119,17 @@ describe('TrackGridPanel lasso selection', () => {
     expect(onRegionLassoSelection).toHaveBeenCalledWith(['region-b', 'region-a'], { shiftKey: false });
   });
 
+  it('uses the closest intersected region as primary when release is outside all regions', () => {
+    const { container, onRegionLassoSelection } = renderPanel();
+    const firstTrackGrid = container.querySelector('[data-test-id="track-grid-1"]') as HTMLDivElement;
+
+    fireEvent.mouseDown(firstTrackGrid, { clientX: 10, clientY: 10, button: 0 });
+    fireEvent.mouseMove(document, { clientX: 150, clientY: 170 });
+    fireEvent.mouseUp(document, { clientX: 150, clientY: 170 });
+
+    expect(onRegionLassoSelection).toHaveBeenCalledWith(['region-a', 'region-b'], { shiftKey: false });
+  });
+
   it('clears selection on a plain empty-space click', () => {
     const { container, onRegionLassoSelection } = renderPanel();
     const firstTrackGrid = container.querySelector('[data-test-id="track-grid-1"]') as HTMLDivElement;

src/components/track/TrackGridPanel.tsx

@@ -32,6 +32,7 @@ interface TrackGridPanelProps {
   onRegionUpdated?: (regionId: string, updates: Partial<RegionUI>, expectedModelUpdates?: { startBeat: number, length: number }) => void;
   onRegionClick?: (regionId: string, options: RegionClickOptions) => void;
   onRegionLassoSelection?: (regionIds: string[], options: RegionClickOptions) => void;
+  onRegionLassoCommit?: () => void;
   onOpenPianoRoll?: (regionId: string) => void;
   onOpenSpectrogram?: (regionId: string) => void;
   showHybridButtonForAudio?: boolean;
@@ -53,6 +54,7 @@ const TrackGridPanel: React.FC<TrackGridPanelProps> = ({
   onRegionUpdated,
   onRegionClick,
   onRegionLassoSelection,
+  onRegionLassoCommit,
   onOpenPianoRoll,
   onOpenSpectrogram,
   showHybridButtonForAudio,
@@ -160,12 +162,36 @@ const TrackGridPanel: React.FC<TrackGridPanelProps> = ({
       });
 
       const intersectedRegionIds = intersectedRegions.map(region => region.id);
-      if (releaseRegionIndex > -1) {
-        const [releaseRegionId] = intersectedRegionIds.splice(releaseRegionIndex, 1);
-        intersectedRegionIds.push(releaseRegionId);
+      if (intersectedRegionIds.length > 0) {
+        const primaryRegionIndex = releaseRegionIndex > -1
+          ? releaseRegionIndex
+          : intersectedRegions.reduce((closestIndex, region, index, allRegions) => {
+              const regionLeft = (region.barNumber - 1) * barWidth;
+              const regionRight = regionLeft + (region.length * barWidth);
+              const regionTop = region.trackIndex * 120;
+              const regionBottom = regionTop + 120;
+              const regionCenterX = (regionLeft + regionRight) / 2;
+              const regionCenterY = (regionTop + regionBottom) / 2;
+              const regionDistance = Math.hypot(releasePointX - regionCenterX, releasePointY - regionCenterY);
+
+              const closestRegion = allRegions[closestIndex];
+              const closestLeft = (closestRegion.barNumber - 1) * barWidth;
+              const closestRight = closestLeft + (closestRegion.length * barWidth);
+              const closestTop = closestRegion.trackIndex * 120;
+              const closestBottom = closestTop + 120;
+              const closestCenterX = (closestLeft + closestRight) / 2;
+              const closestCenterY = (closestTop + closestBottom) / 2;
+              const closestDistance = Math.hypot(releasePointX - closestCenterX, releasePointY - closestCenterY);
+
+              return regionDistance < closestDistance ? index : closestIndex;
+            }, 0);
+
+        const [primaryRegionId] = intersectedRegionIds.splice(primaryRegionIndex, 1);
+        intersectedRegionIds.push(primaryRegionId);
       }
 
       onRegionLassoSelection?.(intersectedRegionIds, { shiftKey: isLassoShiftPressedRef.current });
+      onRegionLassoCommit?.();
     }
 
     isLassoSelectingRef.current = false;