fix: instrument load from PIANO_ROLL in SECTION-TAB writes to main

updateActiveTracksRef checks sessionTabs by currentActiveTab.
When activeTab is a PIANO_ROLL sub-tab (midi_xxx), none matches
-> falls to setTracks (main). Instrument changes are lost.
Fix: also check subTabs for PIANO_ROLL type, resolve parent
session tab via parent_tab_id, route to setSessionTabs.

app/static/js/app.jsx

@@ -12380,12 +12380,20 @@ const App = () => {
   const updateActiveTracksRef = useCallback(updater => {
     const currentSessionTabs = sessionTabsRef.current;
     const currentActiveTab = activeTabRef.current;
-    const st = currentSessionTabs.find(s => s.id === currentActiveTab);
+    var st = currentSessionTabs.find(s => s.id === currentActiveTab);
     if (st) {
       setSessionTabs(prev => prev.map(s => s.id === currentActiveTab ? { ...s, tracks: updater(s.tracks), isDirty: true } : s));
-    } else {
-      setTracks(updater);
+      return;
     }
+    var pr = subTabsRef.current ? subTabsRef.current.find(s => s.id === currentActiveTab && s.type === 'PIANO_ROLL') : null;
+    if (pr && pr.parent_tab_id && pr.parent_tab_id.startsWith('session_')) {
+      var parentSt = currentSessionTabs.find(s => s.id === pr.parent_tab_id);
+      if (parentSt) {
+        setSessionTabs(prev => prev.map(s => s.id === pr.parent_tab_id ? { ...s, tracks: updater(s.tracks), isDirty: true } : s));
+        return;
+      }
+    }
+    setTracks(updater);
   }, []);
   const updateActiveTracks = updateActiveTracksRef;