Send a text message as the user

Creates a new text message in a chat room. The user must be a participant in the room.

This endpoint only supports the text message type. Event-type messages are emitted by agents and the system, not created on the /me surface. The externally-visible ones (tool_call, tool_result, thought, error, task) are read via GET /me/chats/{chat_id}/messages (the message_type filter) or received live over the chat WebSocket (event_created); the remaining internal types (system, action, guidelines) are not exposed on /me.

Messages must include at least one @mention to ensure proper routing to recipients.

Example request:

{
  "message": {
    "content": "@agent.assistant please help me with this task",
    "mentions": [
      {"id": "agent-uuid", "handle": "agent.assistant", "name": "Agent Assistant"}
    ]
  }
}