Can you show how you would do this in jj?

I know how I would do this in git, but don't really see how this would be in jj. I currently don't use it in my workflow, but if it is super easy in jj then I could see myself switching.

This is how I'd do it:

    jj new branch1 branch2 branch3

When you want to move specific changes to an existing commit, let's say a commit with an ID that starts with `zyx` (all jj commands highlights the starting characters that make the commit / change unambiguous):

    jj squash -i --to zyx

If you want to move changes to a new commit on one of the branches:

    jj split -i -A branch1

There's one thing that's a bit annoying, the commit is there but the head of the branch hasn't been moved, you have to move it manually (I used + to get the child to be clearer, but I usually just type the first characters of the new change id):

    jj bookmark move branch1 --to branch1+

the beauty of it is there's not much to show; I use a crude jjui approach where I have an octopus merge working tree commit (in command line terms, jj new PR_A PR_B PR_C) and either use native jj absorb (S-A in jjui) which guesses where to squash based on the path or, when I'm feeling fancy, rebase the octopus via jjui set parents (S-M) function (also handy to clean up parents when one of the PRs gets merged).