> I (Martin von Zweigbergk) have almost exclusively used `jj` to develop the project itself since early January 2021. I haven't had to re-clone from source (I don't think I've even had to restore from backup).

WTF?? Me neither on none of my git project. Ever. So what? I’m a git genius?? The truth is I don’t even understand how one can reach a point where re-cloning a (git) repo is needed: git can always reset --hard and it has never ever failed for me, even during complicated interactive rebase and co.