fix: sync notes from st.notes + set isPlaying for playhead + metronome count-in

app/static/js/app.jsx

@@ -4583,6 +4583,7 @@ const PianoRollTabEditor = ({ st, zoom, bpm, viewportWidth, onClose, onUpdateNot
   const viewBeats = Math.ceil(viewWidth / pixelsPerBeat) + 4;
 
   const [notes, setNotes] = React.useState(st.notes || []);
+  React.useEffect(() => { setNotes(st.notes || []); }, [st.notes]);
   const brushVelocityRef = React.useRef(0.8);
   const [selectedNoteIds, setSelectedNoteIds] = React.useState([]);
 
@@ -9864,7 +9865,7 @@ const App = () => {
     setRecTempMidiNotes([]);
     const ctx = getAudioContext();
     const silentBuf = ctx.createBuffer(1, 128, ctx.sampleRate);
-    setSubTabs(prev => prev.map(s => s.id === tab.id ? { ...s, buffer: silentBuf } : s));
+    setSubTabs(prev => prev.map(s => s.id === tab.id ? { ...s, buffer: silentBuf, isPlaying: true } : s));
     startSubTabPlayback({ ...tab, buffer: silentBuf }, startTime);
     startOffsetTimeRef.current = startTime;
     startAudioTimeRef.current = context.currentTime;