add message id (#21214)

backend/open_webui/env.py

@@ -209,6 +209,9 @@ FORWARD_USER_INFO_HEADER_USER_ROLE = os.environ.get(
 )
 
 # Header name for chat ID forwarding (customizable via environment variable)
+FORWARD_SESSION_INFO_HEADER_MESSAGE_ID = os.environ.get(
+    "FORWARD_SESSION_INFO_HEADER_MESSAGE_ID", "X-OpenWebUI-Message-Id"
+)
 FORWARD_SESSION_INFO_HEADER_CHAT_ID = os.environ.get(
     "FORWARD_SESSION_INFO_HEADER_CHAT_ID", "X-OpenWebUI-Chat-Id"
 )