fix(langchain_v1): initialize variables in _fetch_last_ai_and_tool_messages

README.md

@@ -34,7 +34,7 @@
   </a>
 </p>
 
-LangChain is a framework for building agents and LLM-powered applications. It helps you chain together interoperable components and third-party integrations to simplify AI application development —  all while future-proofing decisions as the underlying technology evolves.
+LangChain is a framework for building agents and LLM-powered applications. It helps you chain together interoperable components and third-party integrations to simplify AI application development — all while future-proofing decisions as the underlying technology evolves.
 
 ```bash
 pip install langchain

libs/langchain_v1/langchain/agents/factory.py

@@ -1424,15 +1424,17 @@
 def _fetch_last_ai_and_tool_messages(
     messages: list[AnyMessage],
 ) -> tuple[AIMessage, list[ToolMessage]]:
-    last_ai_index: int
-    last_ai_message: AIMessage
-
+    last_ai_index: int | None = None
+    last_ai_message: AIMessage | None = None
     for i in range(len(messages) - 1, -1, -1):
         if isinstance(messages[i], AIMessage):
             last_ai_index = i
             last_ai_message = cast("AIMessage", messages[i])
             break
 
+    if last_ai_message is None or last_ai_index is None:
+        raise ValueError("No AIMessage found in messages list")
+
     tool_messages = [m for m in messages[last_ai_index + 1 :] if isinstance(m, ToolMessage)]
     return last_ai_message, tool_messages