fix(langchain_v1): tool selector should use last human message (#33294)

Author: sydney-runkle

libs/langchain_v1/langchain/agents/middleware/tool_selection.py

@@ -181,7 +181,7 @@ def _prepare_selection_request(self, request: ModelRequest) -> _SelectionRequest
 
         # Get the last user message from the conversation history
         last_user_message: HumanMessage
-        for message in request.messages:
+        for message in reversed(request.messages):
             if isinstance(message, HumanMessage):
                 last_user_message = message
                 break