core[patch]: Fix runnable with message history (#14629)

Fix bug shown in #14458. Namely, that saving inputs to history fails
when the input to base runnable is a list of messages

libs/core/tests/unit_tests/runnables/test_history.py

@@ -1,4 +1,4 @@
-from typing import Any, Callable, Dict, List, Sequence, Union
+from typing import Any, Callable, Dict, List, Optional, Sequence, Union
 
 from langchain_core.messages import AIMessage, BaseMessage, HumanMessage, SystemMessage
 from langchain_core.pydantic_v1 import BaseModel
@@ -18,8 +18,10 @@ def test_interfaces() -> None:
     assert str(history) == "System: system\nHuman: human 1\nAI: ai\nHuman: human 2"
 
 
-def _get_get_session_history() -> Callable[..., ChatMessageHistory]:
-    chat_history_store = {}
+def _get_get_session_history(
+    *, store: Optional[Dict[str, Any]] = None
+) -> Callable[..., ChatMessageHistory]:
+    chat_history_store = store if store is not None else {}
 
     def get_session_history(session_id: str, **kwargs: Any) -> ChatMessageHistory:
         if session_id not in chat_history_store:
@@ -34,13 +36,24 @@ def test_input_messages() -> None:
         lambda messages: "you said: "
         + "\n".join(str(m.content) for m in messages if isinstance(m, HumanMessage))
     )
-    get_session_history = _get_get_session_history()
+    store: Dict = {}
+    get_session_history = _get_get_session_history(store=store)
     with_history = RunnableWithMessageHistory(runnable, get_session_history)
     config: RunnableConfig = {"configurable": {"session_id": "1"}}
     output = with_history.invoke([HumanMessage(content="hello")], config)
     assert output == "you said: hello"
     output = with_history.invoke([HumanMessage(content="good bye")], config)
     assert output == "you said: hello\ngood bye"
+    assert store == {
+        "1": ChatMessageHistory(
+            messages=[
+                HumanMessage(content="hello"),
+                AIMessage(content="you said: hello"),
+                HumanMessage(content="good bye"),
+                AIMessage(content="you said: hello\ngood bye"),
+            ]
+        )
+    }
 
 
 def test_input_dict() -> None: