COMMENTONCOLUMNmessages.agent_idIS'ID of the agent that generated this message. For user messages, this represents the agent that should respond to this message.';
-- Make thread agent_id nullable to allow agent-agnostic threads
-- This is already nullable from the existing migration, but we'll add a comment
COMMENTONCOLUMNthreads.agent_idIS'Optional default agent for the thread. If NULL, agent can be selected per message.';