Body
Central channel ID where the message is posted
Server ID (use '00000000-0000-0000-0000-000000000000' for default)
ID of the message author (user or agent)
The message content text
Source type (e.g., 'agent_response', 'user_message')
Raw message object containing additional data
Optional ID of the message being replied to
Additional metadata including agent_name if from agent