For what it's worth, I've been doing basically this with magit for years now, sometimes with the two-commit setup but usually just using the index plus top commit instead. It's not as slick, though, so this is on my list of things to try out when I give jj a spin eventually.<p>`c F` in the magit menu squashes staged changes directly into a commit in the log, and `c e` amends (which is to say squashing into the tip). So in this case I'd hit `s` to stage, and either `c e` or `c F j C-c C-c` (fixup, move one item down to get to HEAD^, confirm) — both of which are practically atomic operations for me at this point.