Fix delta final priority problem in backend

engine/core/duplex_pipeline.py

@@ -939,7 +939,9 @@ class DuplexPipeline:
                                 text=text_chunk,
                             )
                         },
-                        priority=40,
+                        # Keep delta/final on the same event priority so FIFO seq
+                        # preserves stream order (avoid late-delta after final).
+                        priority=20,
                     )
 
                     while True: