feat: refactor the POST agent/messages API to take multiple messages (#1882)

letta/schemas/message.py

@@ -2,7 +2,7 @@ import copy
 import json
 import warnings
 from datetime import datetime, timezone
-from typing import List, Optional
+from typing import List, Literal, Optional
 
 from pydantic import Field, field_validator
 
@@ -57,7 +57,11 @@ class BaseMessage(LettaBase):
 class MessageCreate(BaseMessage):
     """Request to create a message"""
 
-    role: MessageRole = Field(..., description="The role of the participant.")
+    # In the simplified format, only allow simple roles
+    role: Literal[
+        MessageRole.user,
+        MessageRole.system,
+    ] = Field(..., description="The role of the participant.")
     text: str = Field(..., description="The text of the message.")
     name: Optional[str] = Field(None, description="The name of the participant.")