fix: piano roll spectrogram is not being zoomed correctly; switching from MIDI region to audio region with piano roll open might cause residual notes.

src/components/piano-roll/PianoGrid.tsx

@@ -32,6 +32,7 @@ interface PianoGridProps {
   bpm?: number;
   spectrogramThresholdDb?: number;
   spectrogramPower?: number;
+  pianoRollZoom?: number;
   mode?: 'midi-edit' | 'spectrogram' | 'hybrid';
 }
 
@@ -60,6 +61,7 @@ const PianoGrid: React.FC<PianoGridProps> = ({
   bpm = 120,
   spectrogramThresholdDb = -25,
   spectrogramPower = 0.5,
+  pianoRollZoom = 1,
 }) => {
   const [cursorPosition, setCursorPosition] = useState<CursorPosition | null>(null);
   const [isModifierPressed, setIsModifierPressed] = useState(false);
@@ -240,6 +242,7 @@ const PianoGrid: React.FC<PianoGridProps> = ({
             bpm={bpm}
             thresholdDb={spectrogramThresholdDb}
             power={spectrogramPower}
+            zoom={pianoRollZoom}
           />
         )}
 

src/components/piano-roll/PianoRoll.tsx

@@ -158,22 +158,22 @@ const PianoRoll: React.FC<PianoRollProps> = ({
       return;
     }
 
-    // Find the region in the tracks
+    let found: KGMidiRegion | null = null;
     for (const track of tracks) {
-      const regions = track.getRegions();
+      const region = track.getRegions().find(r => r.getId() === regionId);
-      const region = regions.find(r => r.getId() === regionId);
-      
       if (region && region instanceof KGMidiRegion) {
-        setActiveRegion(region);
+        found = region;
-        
-        if (DEBUG_MODE.PIANO_ROLL) {
-          console.log(`Active region set in PianoRoll: ${region.getId()}`);
-          console.log(`Region details: name=${region.getName()}, trackId=${region.getTrackId()}, trackIndex=${region.getTrackIndex()}`);
-        }
-        
         break;
       }
     }
+
+    // Always update — clears stale MIDI region when switching to an audio region
+    setActiveRegion(found);
+
+    if (found && DEBUG_MODE.PIANO_ROLL) {
+      console.log(`Active region set in PianoRoll: ${found.getId()}`);
+      console.log(`Region details: name=${found.getName()}, trackId=${found.getTrackId()}, trackIndex=${found.getTrackIndex()}`);
+    }
   }, [regionId, tracks]);
 
   // Sync local state with KGPianoRollState on mount
@@ -965,6 +965,7 @@ const PianoRoll: React.FC<PianoRollProps> = ({
         bpm={bpm}
         spectrogramThresholdDb={spectrogramThresholdDb}
         spectrogramPower={spectrogramPower}
+        pianoRollZoom={pianoRollZoom}
       />
       
       <div 

src/components/piano-roll/PianoRollContent.tsx

@@ -34,6 +34,7 @@ interface PianoRollContentProps {
   bpm?: number;
   spectrogramThresholdDb?: number;
   spectrogramPower?: number;
+  pianoRollZoom?: number;
 }
 
 const PianoRollContent: React.FC<PianoRollContentProps> = ({
@@ -56,6 +57,7 @@ const PianoRollContent: React.FC<PianoRollContentProps> = ({
   bpm = 120,
   spectrogramThresholdDb = -25,
   spectrogramPower = 0.5,
+  pianoRollZoom = 1,
 }) => {
   const isSpectrogram = mode === 'spectrogram';
   // Get KGCore instance
@@ -234,7 +236,7 @@ const PianoRollContent: React.FC<PianoRollContentProps> = ({
         />
       );
     });
-  }, [activeRegion, noteUpdateCounter, resizingNoteId, draggingNoteId, tempNoteStyles, selectedNoteIds, selectionBoxRender, tracks]);
+  }, [mode, activeRegion, noteUpdateCounter, resizingNoteId, draggingNoteId, tempNoteStyles, selectedNoteIds, selectionBoxRender, tracks]);
 
   const recordingNoteOverlays = useMemo(() => {
     if (!isRecording || !activeRegion || recordingNotes.length === 0) return null;
@@ -281,6 +283,7 @@ const PianoRollContent: React.FC<PianoRollContentProps> = ({
           bpm={bpm}
           spectrogramThresholdDb={spectrogramThresholdDb}
           spectrogramPower={spectrogramPower}
+          pianoRollZoom={pianoRollZoom}
         >
           {memoizedNotes}
           {!isSpectrogram && recordingNoteOverlays}

src/components/piano-roll/SpectrogramCanvas.tsx

@@ -12,6 +12,7 @@ interface SpectrogramCanvasProps {
   bpm: number;
   thresholdDb: number;
   power: number;
+  zoom: number;
 }
 
 const PITCH_BINS = 128;
@@ -53,6 +54,7 @@ const SpectrogramCanvas: React.FC<SpectrogramCanvasProps> = ({
   bpm,
   thresholdDb,
   power,
+  zoom,
 }) => {
   const canvasRef = useRef<HTMLCanvasElement | null>(null);
   const [loading, setLoading] = useState(true);
@@ -62,6 +64,11 @@ const SpectrogramCanvas: React.FC<SpectrogramCanvasProps> = ({
   const rawResultRef = useRef<SpectrogramResult | null>(null);
   const sampleRateRef = useRef<number>(44100);
   const regionDurationRef = useRef<number>(0);
+  // Natural (1x) canvas pixel width — set after each draw, used to apply zoom as CSS stretch
+  const naturalWidthRef = useRef<number>(0);
+  // Always-current zoom without making it a renderSpectrogram dependency
+  const zoomRef = useRef(zoom);
+  useEffect(() => { zoomRef.current = zoom; }, [zoom]);
 
   const renderSpectrogram = useCallback((
     result: SpectrogramResult,
@@ -75,13 +82,12 @@ const SpectrogramCanvas: React.FC<SpectrogramCanvasProps> = ({
     const ctx = canvas.getContext('2d');
     if (!ctx) return;
 
-    const beatWidth =
-      parseInt(getComputedStyle(document.documentElement).getPropertyValue('--region-grid-beat-width')) || 40;
     const noteHeight =
       parseInt(getComputedStyle(document.documentElement).getPropertyValue('--region-piano-key-height')) || 20;
 
     const totalBeats = (regionDurationSeconds * bpm) / 60;
-    const canvasWidth = Math.ceil(totalBeats * beatWidth);
+    // Always draw at 1x resolution; zoom is applied as CSS width stretch
+    const canvasWidth = Math.ceil(totalBeats * 40);
     const canvasHeight = PITCH_BINS * noteHeight;
 
     // Convert dB threshold to linear: values below this → black
@@ -131,6 +137,11 @@ const SpectrogramCanvas: React.FC<SpectrogramCanvasProps> = ({
     ctx.imageSmoothingEnabled = true;
     ctx.imageSmoothingQuality = 'high';
     ctx.drawImage(offscreen, 0, 0, canvasWidth, canvasHeight);
+
+    // Store natural width and apply current zoom as CSS stretch (no pixel recompute on zoom)
+    naturalWidthRef.current = canvasWidth;
+    canvas.style.width = `${canvasWidth * zoomRef.current}px`;
+    canvas.style.height = `${canvasHeight}px`;
   }, [bpm]);
 
   // Re-render without re-running the worker when threshold or power changes
@@ -146,6 +157,14 @@ const SpectrogramCanvas: React.FC<SpectrogramCanvasProps> = ({
     }
   }, [thresholdDb, power, renderSpectrogram]);
 
+  // Zoom changes: stretch width only, pin height to canvas pixel height
+  useEffect(() => {
+    if (canvasRef.current && naturalWidthRef.current > 0) {
+      canvasRef.current.style.width = `${naturalWidthRef.current * zoom}px`;
+      canvasRef.current.style.height = `${canvasRef.current.height}px`;
+    }
+  }, [zoom]);
+
   // Load audio + run worker when the audio region itself changes
   useEffect(() => {
     let cancelled = false;