The bit that made this click for me: it works on any commit in history, not just HEAD. Mark the commit as edit in git rebase -i, then git reset HEAD^ to uncommit it while keeping the changes in the working tree, and rebuild the pieces from there. git add -p is the real workhorse for the rebuild: s splits a hunk into smaller ones, and e lets you hand-edit the hunk when the boundary doesn't fall on clean line breaks. S…
Or the opposite direction, with repeated "git checkout -p ..." and commit steps. Slightly less comfortable because you have to figure out (such as from "git rebase --edit-todo") the later commit, but it makes testing the pieces easier.
hadn't thought of building forward like that. being able to test each slice before committing beats finding out after the rebase that half of them don't compile. thanks, stealing this