Figma comment threads seem to have broken ordering

It's a bit hard to tell, but the parent of the thread doesn't appear in the timeline in Element, and the ordering of messages looks wrong.

Start by locating the Figma comment-thread handling and the code that builds the Element timeline. Reproduce a thread with replies and compare the rendered order, checking whether the parent is included. Done means the parent appears in the timeline and the messages follow the thread's correct order.

Written by the indexing model from the issue text.