mutation ReplyToGitHubReviewThread($threadId: ID!, $body: String!) {
  replyToGitHubReviewThread(threadId: $threadId, body: $body) {
    id
    body
    bodyText
    bodyHtml
    url
    author {
      login
      avatarUrl
      url
    }
  }
}

{
  "threadId": "id",
  "body": "string"
}

{
  "data": {
    "replyToGitHubReviewThread": {
      "id": "id",
      "body": "string",
      "bodyText": "string",
      "bodyHtml": "string",
      "url": "string",
      "author": {
        "login": "string",
        "avatarUrl": "string",
        "url": "string"
      }
    }
  }
}