Feature request: scroll to first unread message in chat

When there are unread chat messages, Keybase chat separates them with a red line from the old ones. That is very useful because often one wants to read all new messages in the chat to get context for current discussion. If there are too many new messages, however, it can be hard to find the first unread one as there is no indication of how many new messages there are in the channel. It would be handy to have such an indication available, along with an option to scroll to the first unread message.

Start by locating the chat message list and the existing red unread-message separator in the client. Trace how unread state is represented and how scrolling or navigation is triggered; done should include a visible unread-count indication and an option to reach the first unread message.

Written by the indexing model from the issue text.