Order by timestamp within the categorized room lists
Order by timestamp within the categorized room lists

When we load the page, all encrypted events arrive well after we've generated our initial grouping which can cause them to jump to the top of their categories wrongly. For direct chats, this meant that people who don't have a lot of unread messages would see ancient rooms bubbling to the top for no reason after the page has loaded.

We still have to track when the last category change was (ie: when we switched from red -> grey) so that when the category doesn't exist in the list we can insert the room at the right place (the start of the last category when we switch beyond the order expected).
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