diff --git a/app/core/fx_realtime.py b/app/core/fx_realtime.py
index 1fe0fdd..9903293 100644
--- a/app/core/fx_realtime.py
+++ b/app/core/fx_realtime.py
@@ -175,10 +175,13 @@ class FxRealtimeSession:
             json.dump(job, f)
         cmd = [exe, "--realtime-fx", self._job_path, "--shm", self.name,
                "--parent", str(os.getpid())]
+        # FXRT_BRIDGE_LOG=<path>: bat stderr bridge (FxRTPerf) vao file — chan
+        # doan outFull/drop; mac dinh DEVNULL nhu cu.
+        _blog = os.environ.get("FXRT_BRIDGE_LOG") or ""
         self.proc = subprocess.Popen(
             cmd,
             stdout=subprocess.DEVNULL,
-            stderr=subprocess.DEVNULL,
+            stderr=open(_blog, "ab", buffering=0) if _blog else subprocess.DEVNULL,
             creationflags=getattr(subprocess, "CREATE_NO_WINDOW", 0),
         )