fix: piano roll zoom/scroll + AI copilot + SF cache + auto-scroll drag

app/core/vst_engine.py

@@ -1,6 +1,7 @@
 # SonicForge Studio VST / VSTi Engine Service
 import os
 import numpy as np
+import functools
 from ctypes import c_int, c_char_p, c_void_p
 
 def midi_note_to_freq(note_number: int) -> float:
@@ -92,11 +93,62 @@ if HAS_PYFLUIDSYNTH:
         HAS_PYFLUIDSYNTH = False
 
 
+# ── Module-level caches ──
+_FLUID_CACHE = {}  # path → (fluidsynth.FluidSynth, refcount)
+_PLUGIN_MANAGER_INSTANCE = None
+_PLUGIN_MANAGER_ARGS = None
+_SF_INSTRUMENTS_CACHE = {}  # sf_id → list[presets]
+
+def get_plugin_manager(vst_dir="/opt/daw_engine/vst3", sf_dir="/opt/daw_engine/soundfonts", upload_sf_dir=None) -> "PluginManager":
+    """Singleton: reuse PluginManager when args match, else create new."""
+    global _PLUGIN_MANAGER_INSTANCE, _PLUGIN_MANAGER_ARGS
+    args = (vst_dir, sf_dir, upload_sf_dir)
+    if _PLUGIN_MANAGER_INSTANCE is not None and _PLUGIN_MANAGER_ARGS == args:
+        return _PLUGIN_MANAGER_INSTANCE
+    _PLUGIN_MANAGER_ARGS = args
+    _PLUGIN_MANAGER_INSTANCE = PluginManager(vst_dir, sf_dir, upload_sf_dir)
+    return _PLUGIN_MANAGER_INSTANCE
+
+def load_soundfont_cached(path: str):
+    """Return a cached FluidSynth instance for path, incrementing refcount."""
+    global _FLUID_CACHE
+    if not HAS_PYFLUIDSYNTH:
+        return None
+    if path in _FLUID_CACHE:
+        fl, ref = _FLUID_CACHE[path]
+        _FLUID_CACHE[path] = (fl, ref + 1)
+        return fl
+    try:
+        import fluidsynth
+        fl = fluidsynth.FluidSynth(sample_rate=44100, gain=0.5)
+        font_id = fl.sfload(path)
+        fl.program_select(0, font_id, 0, 0)
+        _FLUID_CACHE[path] = (fl, 1)
+        return fl
+    except Exception:
+        return None
+
+def release_soundfont(path: str):
+    """Decrement refcount; delete FluidSynth when count reaches 0."""
+    global _FLUID_CACHE
+    if path not in _FLUID_CACHE:
+        return
+    fl, ref = _FLUID_CACHE[path]
+    if ref <= 1:
+        try:
+            fl.delete()
+        except Exception:
+            pass
+        del _FLUID_CACHE[path]
+    else:
+        _FLUID_CACHE[path] = (fl, ref - 1)
+
 class PluginManager:
     def __init__(self, vst_dir="/opt/daw_engine/vst3", sf_dir="/opt/daw_engine/soundfonts", upload_sf_dir=None):
         self.vst_dir = vst_dir
         self.sf_dir = sf_dir
         self.upload_sf_dir = upload_sf_dir
+        self._sf_scan_cache = None  # cache for _scan_soundfonts()
 
     def _scan_plugins(self) -> dict:
         plugins = {}
@@ -160,20 +212,20 @@ class PluginManager:
                     pass
         return vst
 
+    def _scan_soundfonts_cached(self):
+        if self._sf_scan_cache is not None:
+            return self._sf_scan_cache
+        self._sf_scan_cache = self._scan_soundfonts()
+        return self._sf_scan_cache
+
     def load_soundfont(self, path: str):
-        if not HAS_PYFLUIDSYNTH:
-            return None
-        try:
-            fl = fluidsynth.FluidSynth(sample_rate=44100, gain=0.5)
-            font_id = fl.sfload(path)
-            fl.program_select(0, font_id, 0, 0)
-            return fl
-        except Exception:
-            return None
+        return load_soundfont_cached(path)
 
     def list_soundfont_instruments(self, sf_id: str):
         if not ensure_pyfluidsynth():
             return []
+        if sf_id in _SF_INSTRUMENTS_CACHE:
+            return _SF_INSTRUMENTS_CACHE[sf_id]
         search_dirs = []
         if os.path.isdir(self.sf_dir):
             search_dirs.append(self.sf_dir)
@@ -187,13 +239,13 @@ class PluginManager:
                 if base == sf_id or base == sf_id.replace("sf_", ""):
                     path = os.path.join(d, f)
                     try:
+                        import fluidsynth
                         fl = fluidsynth.Synth()
                         fid = fl.sfload(path)
                         if fid < 0:
                             fl.delete()
                             continue
                         presets = []
-                        # Use fluid_sfont_get_preset + fluid_preset_get_name C API
                         _fl = fluidsynth._fl
                         _fl.fluid_synth_get_sfont_by_id.restype = c_void_p
                         _fl.fluid_preset_get_name.restype = c_char_p
@@ -217,9 +269,11 @@ class PluginManager:
                                                     "name": name_val.decode("utf-8", errors="replace")
                                                 })
                         fl.delete()
+                        _SF_INSTRUMENTS_CACHE[sf_id] = presets[:256]
                         return presets[:256]
                     except Exception:
                         import traceback; traceback.print_exc()
+        _SF_INSTRUMENTS_CACHE[sf_id] = []
         return []
 
     def list_available(self) -> dict: