fix: lag khi ARM sau reload + câm sau vài lần nhấn MIDI - dedup loadSoundFont (1 font=1 sfload, tránh cạn heap 256MB) + preload instrument khi mở/khôi phục dự án

app/static/js/services/soundfontPlayer.js

@@ -23,6 +23,8 @@
     let _activeOscillators = {};
     let _gainNode = null;
     let _scheduledNotes = [];
+    let _loadPromises = {};
+    let _sfloadSeq = 0;
 
     const getCtx = function () {
         if (_audioCtx) {
@@ -186,7 +188,7 @@
         },
 
         _tryLoadSFL: function (buf, ext) {
-            var fname = '/' + ext + '_' + Date.now();
+            var fname = '/' + ext + '_' + (++_sfloadSeq) + '_' + Date.now();
             try { _fluidModule.FS.unlink(fname); } catch (e) {}
             _fluidModule.FS.writeFile(fname, new Uint8Array(buf));
             var cPath = this._allocCStr(fname);
@@ -203,6 +205,18 @@
                 _currentSfId = sfId;
                 return true;
             }
+            // Deduplicate concurrent loads: rapid key presses (or several armed
+            // tracks) all call loadSoundFont for the same font before the first
+            // load resolves. Without this, the same soundfont is sfload'd several
+            // times (handles 1,2,3,4…) — wasting the 256MB WASM heap and stalling
+            // notes until each load finishes (audible lag, then silence).
+            if (!_loadPromises[sfId]) {
+                _loadPromises[sfId] = this._doLoadSoundFont(sfId);
+            }
+            return _loadPromises[sfId];
+        },
+
+        _doLoadSoundFont: async function (sfId) {
             try {
                 var cache = window.SonicSFStorage;
                 var buf = cache ? await cache.getBuffer(sfId) : null;