fix(fxrt): mo GUI VST khong gay crackle - GUI spawn BELOW_NORMAL, mien watchdog khi mo native GUI, realtime loop ABOVE_NORMAL

app/api/v1/plugins.py

@@ -698,12 +698,20 @@ async def open_fx_gui(req: FxGuiRequest, current_user: dict = Depends(get_curren
         raise HTTPException(status_code=500, detail="Không ghi được job file cho bridge.")
     cmd = [exe, "--fx-gui" if req.embed else "--open-fx-gui", job_path]
     try:
+        # fx-gui spawn o BELOW_NORMAL: process nay load instance VST THU HAI
+        # (CPU spike vai giay) - neu o NORMAL se preempt realtime audio loop
+        # (fx_vst_bridge --realtime-fx, thread NORMAL) -> underrun -> am "bop
+        # nghet" ngay luc mo GUI roi moi hoi phuc. BELOW_NORMAL cho load GUI
+        # khong canh tranh thread audio.
+        _gui_creationflags = subprocess.CREATE_NO_WINDOW if os.name == "nt" else 0
+        if os.name == "nt":
+            _gui_creationflags |= getattr(subprocess, "BELOW_NORMAL_PRIORITY_CLASS", 0)
         if req.embed:
             proc = subprocess.Popen(cmd, stdout=subprocess.PIPE,
                                     stderr=subprocess.STDOUT, text=True,
                                     close_fds=os.name != "nt",
                                     env=dict(os.environ, SF_PARENT_PID=str(os.getpid())),
-                                    creationflags=subprocess.CREATE_NO_WINDOW if os.name == "nt" else 0)
+                                    creationflags=_gui_creationflags)
             # Bridge prints SF_FXGUI_PORT=<port> after binding its HTTP server.
             embed_url = None
             try:
@@ -741,7 +749,7 @@ async def open_fx_gui(req: FxGuiRequest, current_user: dict = Depends(get_curren
                     "embed_url": embed_url, "cmd": cmd}
         proc = subprocess.Popen(cmd, close_fds=os.name != "nt",
                                 env=dict(os.environ, SF_PARENT_PID=str(os.getpid())),
-                                creationflags=subprocess.CREATE_NO_WINDOW if os.name == "nt" else 0)
+                                creationflags=_gui_creationflags)
         proc._sf_plugin_path = plugin_path
         _register_fx_gui_process(proc)
         return {"success": True, "started": True, "already_running": False, "cmd": cmd}