curl --request POST \
  --url https://api.example.com/a2a/message/send

{
  "jsonrpc": "2.0",
  "id": "request-123",
  "result": {
    "task": {
      "id": "task-456",
      "context_id": "context-789",
      "status": "completed",
      "history": [
        {
          "message_id": "msg-1",
          "role": "agent",
          "parts": [
            {
              "kind": "text",
              "text": "Response from agent"
            }
          ]
        }
      ]
    }
  }
}