In order to make changes to commit A when there are conflicting changes in B, I was thinking that you would have to use interactive rebase instead because you can no longer make those changes in the working copy and use `git commit --fixup`, right? And because there will now be conflicts in commit B, you will be in this "interrupted rebase" state where you have conflicts in the staging area and it's a bit tricky (IMO) to leave those and look around somewhere else and then come back and resolve the conflicts and continue the rebase later.
> Yes, but wouldn't this be the same in JJ, when you do your changes on top of A, and later squash them into D?
The difference is that we don't end up in an interrupted rebase. If we squashed some changes into A and that resulted in conflicts in B, then we would then create a new working-copy commit on top of the conflicted B (I call all of the related commits B even if they've been rewritten - I hope that's not too confusing). We then resolve the conflicts and squash the resolution into B and the resolution gets propagated to the descendants. We are free at any time to check out any other commit etc.; there's no interrupted rebase or unfinished conflicts we need to take care of first. I hope that clarifies.