fix(latency): threadpool renders + RENDER_LOCK + client pre-render cache

app/api/v1/plugins.py

@@ -6,7 +6,7 @@ from fastapi.responses import FileResponse
 from pydantic import BaseModel
 from typing import Optional, Any
 from app.config import settings
-from app.core.vst_engine import PluginManager, HAS_PEDALBOARD, HAS_PYFLUIDSYNTH, apply_preset_to_plugin, render_soundfont_midi_to_audio
+from app.core.vst_engine import PluginManager, HAS_PEDALBOARD, HAS_PYFLUIDSYNTH, apply_preset_to_plugin, render_soundfont_midi_to_audio, RENDER_LOCK, _render_locked
 from app.core.render_engine import PythonRenderEngine, _find_sf2_path, _find_default_sf2
 from app.core.soundfont_inspector import SoundFontInspector
 from app.core.soundfont_converter import SoundFontConverter
@@ -975,6 +975,7 @@ async def midi_render(req: MidiRenderRequest, current_user: dict = Depends(get_c
         )
 
 
+@_render_locked
 def _render_midi_notes_pedalboard(instrument_id: str, notes: list, bpm: float,
                                   sample_rate: int, preset_id=None, preset_path=None,
                                   preset_data_b64=None, soundfont_bank=None,
@@ -1162,7 +1163,7 @@ def _carla_bridge_running() -> bool:
 
 
 @router.post("/render")
-async def render_project(
+def render_project(
     req: RenderRequest,
     current_user: dict = Depends(get_current_user)
 ):