修复重构后的导入错误和缺失模块

backend/app/main_graph/config.py

@@ -0,0 +1,21 @@
+"""
+Main Graph Configuration - Streaming Writer
+"""
+from typing import Optional, Callable, Any
+
+_stream_writer: Optional[Callable[[Any], None]] = None
+
+def set_stream_writer(writer: Callable[[Any], None]):
+    """Set the global stream writer"""
+    global _stream_writer
+    _stream_writer = writer
+
+def get_stream_writer() -> Callable[[Any], None]:
+    """Get the global stream writer"""
+    global _stream_writer
+    if _stream_writer is None:
+        # Default no-op writer
+        def noop(_):
+            pass
+        return noop
+    return _stream_writer