feat(history): Implement map_db_messages_to_langchain utility

backend/src/ea_chatbot/history/utils.py

@@ -0,0 +1,29 @@
+from typing import List
+from langchain_core.messages import BaseMessage, HumanMessage, AIMessage, SystemMessage
+from ea_chatbot.history.models import Message
+
+def map_db_messages_to_langchain(db_messages: List[Message]) -> List[BaseMessage]:
+    """
+    Converts a list of database Message models to LangChain BaseMessage objects.
+    
+    Args:
+        db_messages: List of Message objects from the database.
+        
+    Returns:
+        List of HumanMessage, AIMessage, or SystemMessage objects.
+    """
+    lc_messages: List[BaseMessage] = []
+    
+    for m in db_messages:
+        role = m.role.lower()
+        if role == "user":
+            lc_messages.append(HumanMessage(content=m.content))
+        elif role == "assistant":
+            lc_messages.append(AIMessage(content=m.content))
+        elif role == "system":
+            lc_messages.append(SystemMessage(content=m.content))
+        else:
+            # Default to HumanMessage for unknown roles
+            lc_messages.append(HumanMessage(content=m.content))
+            
+    return lc_messages