fix: passthrough công cụ từ main sang sub

app/templates/index.html

@@ -1869,7 +1869,31 @@
 
             const contextMenuCopy = () => {
                 const track = tracks.find(t => t.id === contextMenu.trackId);
-                if (!track) return;
+                if (!track || !track.buffer) return;
+                
+                const sr = track.buffer.sampleRate;
+                const data = track.buffer.getChannelData(0);
+                
+                // Copy selected region if selection exists
+                if (selLeft !== null && selRight !== null && selRight > selLeft) {
+                    const trackStart = track.startTime || 0;
+                    const relSelLeft = Math.max(0, selLeft - trackStart);
+                    const relSelRight = Math.max(0, selRight - trackStart);
+                    const startSample = Math.floor(relSelLeft * sr);
+                    const endSample = Math.min(data.length, Math.floor(relSelRight * sr));
+                    const len = endSample - startSample;
+                    if (len > 0) {
+                        const ctx = getAudioContext();
+                        const clipBuffer = ctx.createBuffer(1, len, sr);
+                        clipBuffer.copyToChannel(data.subarray(startSample, endSample), 0);
+                        clipboardRef.current = { buffer: clipBuffer, name: track.name, volume: track.volume, color: track.color };
+                        closeContextMenu();
+                        showToast('Đã sao chép vùng chọn.', 'info');
+                        return;
+                    }
+                }
+                
+                // No selection: copy entire track
                 clipboardRef.current = {
                     buffer: track.buffer,
                     name: track.name,
@@ -1877,7 +1901,7 @@
                     color: track.color,
                 };
                 closeContextMenu();
-                showToast('Đã sao chép track vào clipboard.', 'info');
+                showToast('Đã sao chép toàn bộ track.', 'info');
             };
 
             const contextMenuCut = () => {