I haven't used Atuin (though I think I might give it a try), but maybe you could use the atuin history list command and pipe that into something like fzf or ripgrep to get case insensitive search?

I'm cautiously optimistic that this isn't a warning sign. I can imagine wanting to do something new after spending so long working on one project, but if he left because things were straying from his vision of Signal that could be a bad sign.