Get the replies of a thread as a cursor-paged envelope { items, hasMore, nextBefore }, paged like
GET /messages with paginated=true: the first page holds the newest limit replies (default 50, max 100),
each page is oldest-first, and before=<nextBefore> fetches the next older page until hasMore is false.
If the cursor message was deleted between two calls, the request fails with 409; restart from the newest
page. Only messages with a thread object have replies.
Bearer <token>.Ok