This looks cool. I honestly haven’t ever thought about using vertical tabs in a terminal window but that seems nice.
One question though, have you thought about trying to upstream any of this into Ghostty instead of making an entirely different app?
VSCode has vertical tabs for it's terminals like this, but on the right side.
Upstreaming into Ghostty would be very difficult as it's not actually a fork, I just used libghostty under the hood.