master strip: L/R volume + LINK + MUTE that, bo soloBtn

app/core/render_engine.py

@@ -829,10 +829,25 @@ class PythonRenderEngine:
                 else:
                     logger.warning("[RenderEngine] Masterbus FX cần RENDER_ENGINE=bridge — bỏ qua")
 
-            # Master bus volume (spec §2 Step 4: master gain stage after chain)
-            master_vol_db = master.get("volume_db", 0.0)
-            if master_vol_db:
-                master_buffer *= 10 ** (master_vol_db / 20.0)
+            # Master bus volume (spec §2 Step 4: master gain stage after chain).
+            # Per-channel L/R faders: volumeL_db/volumeR_db (link_lr -> R theo L);
+            # MUTE zeroes output; fallback volume_db cho project cu.
+            if master.get("muted") or master.get("mute"):
+                master_buffer *= 0.0
+            else:
+                vol_l = master.get("volumeL_db", master.get("volume_db", 0.0))
+                if master.get("link_lr"):
+                    vol_r = vol_l
+                else:
+                    vol_r = master.get("volumeR_db", vol_l)
+                if master_buffer.shape[0] >= 2:
+                    if vol_l:
+                        master_buffer[0] *= 10 ** (vol_l / 20.0)
+                    if vol_r:
+                        master_buffer[1] *= 10 ** (vol_r / 20.0)
+                else:
+                    if vol_l:
+                        master_buffer *= 10 ** (vol_l / 20.0)
 
             # Normalization to prevent clipping
             max_peak = np.max(np.abs(master_buffer))