fix(render): resolve VSTi offline qua plugin_dirs user + plugin_path schema

_resolve_instrument dùng PluginManager() chỉ scan VST_DIR mặc định -> VSTi
trong thư mục user (vd Steinberg\VSTPlugins\DUNE 3.dll) 404 -> render_engine
fallback oscillator synth -> bounce sai tiếng. Dùng get_plugin_manager()
(gộp plugin_dirs user) + resolve_plugin_path (lưới an toàn, chặn ext lạ).
render_offline nhận plugin_path từ schema synth_engine.plugin_path ưu tiên.

app/core/native_render.py

@@ -104,9 +104,20 @@ def classify_instrument(path: str) -> int:
 
 
 def _resolve_instrument(instrument_id: str):
-    from app.core.vst_engine import PluginManager
-    path = PluginManager()._scan_plugins().get(instrument_id)
+    from app.core.vst_engine import get_plugin_manager, resolve_plugin_path
+    # get_plugin_manager gộp plugin_dirs user (Plugin Manager) — bản cũ dùng
+    # PluginManager() chỉ scan VST_DIR mặc định → VSTi trong thư mục user
+    # (vd C:\Program Files\Steinberg\VSTPlugins) 404 → render_engine fallback
+    # oscillator synth → bounce sai tiếng ("synthwave lạ"). resolve_plugin_path
+    # là lưới an toàn thứ 2 (so tên file case-insensitive, walk cả dir user).
+    path = get_plugin_manager()._scan_plugins().get(instrument_id)
     if not path:
+        path = resolve_plugin_path(instrument_id)
+    if not path:
+        return None, None
+    # resolve_plugin_path so theo stem — chặn false positive (vd Synapse Audio
+    # → Synapse Audio.nksf, preset file không phải plugin).
+    if not path.lower().endswith((".vst3", ".dll", ".so", ".sf2", ".sf3", ".sfz")):
         return None, None
     return classify_instrument(path), path
 
@@ -187,13 +198,21 @@ def _run_notes_job(job: dict, label: str) -> tuple:
 
 def render_offline(instrument_id, notes, bpm, sample_rate, preset_id=None,
                    preset_path=None, preset_data_b64=None,
-                   soundfont_bank=None, soundfont_program=None) -> tuple:
+                   soundfont_bank=None, soundfont_program=None,
+                   plugin_path=None) -> tuple:
     """Render MIDI notes qua native_bridge --render → (out_path, duration_sec).
 
     Giữ response shape của _render_midi_notes_pedalboard. Lỗi → HTTPException
     (404 instrument lạ, 501 thiếu bridge, 500 lỗi render — file rác bị xóa).
     """
-    itype, path = _resolve_instrument(instrument_id)
+    itype, path = None, None
+    # plugin_path (từ schema synth_engine.plugin_path) ưu tiên — không phụ
+    # thuộc scan; fallback resolve theo tên instrument_id.
+    if plugin_path and os.path.exists(plugin_path):
+        path = os.fspath(plugin_path)
+        itype = classify_instrument(path)
+    if not path:
+        itype, path = _resolve_instrument(instrument_id)
     if not path:
         raise HTTPException(
             status_code=404,

app/core/render_engine.py

@@ -624,6 +624,7 @@ class PythonRenderEngine:
                                             preset_data_b64=se2.get("preset_data") or track.get("preset_data"),
                                             soundfont_bank=soundfont_bank,
                                             soundfont_program=soundfont_program,
+                                            plugin_path=se2.get("plugin_path") or track.get("plugin_path"),
                                         )
                                         synth_buffer, _ = sf.read(out_path, dtype="float32")
                                         if synth_buffer.ndim == 1: