refactor: Rebuild HumanMessages in load_lc_prompt if they are instances of BaseMessage

src/backend/base/langflow/schema/message.py

@@ -3,7 +3,7 @@ from typing import Annotated, Any, AsyncIterator, Iterator, Optional
 
 from fastapi.encoders import jsonable_encoder
 from langchain_core.load import load
-from langchain_core.messages import AIMessage, BaseMessage, HumanMessage
+from langchain_core.messages import AIMessage, BaseMessage, HumanMessage, SystemMessage
 from langchain_core.prompt_values import ImagePromptValue
 from langchain_core.prompts import BaseChatPromptTemplate, ChatPromptTemplate, PromptTemplate
 from langchain_core.prompts.image import ImagePromptTemplate
@@ -123,7 +123,21 @@ class Message(Data):
     def load_lc_prompt(self):
         if "prompt" not in self:
             raise ValueError("Prompt is required.")
-        return load(self.prompt)
+        loaded_prompt = load(self.prompt)
+        # Rebuild HumanMessages if they are instance of BaseMessage
+        if isinstance(loaded_prompt, ChatPromptTemplate):
+            messages = []
+            for message in loaded_prompt.messages:
+                if isinstance(message, HumanMessage):
+                    messages.append(message)
+                elif message.type == "human":
+                    messages.append(HumanMessage(content=message.content))
+                elif message.type == "system":
+                    messages.append(SystemMessage(content=message.content))
+                elif message.type == "ai":
+                    messages.append(AIMessage(content=message.content))
+            loaded_prompt.messages = messages
+        return loaded_prompt
 
     @classmethod
     def from_lc_prompt(