Zulip: Posting and deleting a message in an old topic leaves the topic higher than it should be in the stream topic list

[SaschaMann]

If you post a message in a topic that's long been buried in the topic list to the left, and then delete your new message, the topic stays on top of the list, even if the latest message is months old.

[zulipbot]

Hello @zulip/server-message-view members, this issue was labeled with the "area: message-editing" label, so you may want to check it out!

[timabbott]

This is a tricky issue; the problem is that we order things in the sidebars based on the latest message ID, but for performance reasons don't store every single message ID in every topic in the frontend. As a result, when the latest message gets deleted, the frontend doesn't have an easy thing it can do to compute the second-latest message ID.

I had thought our solution was generally to just delete the topic's data and recompute, however, so something is wrong here.

@amanagr can you investigate?

[amanagr]

Yes, on it. @zulipbot claim