If you do want to solve this, here's two thoughts on how you can deal with it. First: don't try to edit jj changes. Always work on a new change and then squash that in to the parent. You think of that top level change as your working space.

From there, the simplest way is to just always use 'jj commit -i' and 'jj squash -i' to create change ids with your work. Then if you want to have your changes move around with you, just rebase your working copy which contains your "uncommitted files" to the new branch.

A different idea is to put those changes in a separate change, and then when you do work, always create your working space change as a merge change like 'jj new <uncommitted file change id> <main change id>. Then you should be able to do 'jj absorb' instead of 'jj squash' to put changes into the right change. Switching to a different branch is 'jj new <uncommitted file change id> <other change id>.

As in typing this, I'm thinking for myself and what I actually do in practice... I find moving / rebasing jj commits very easy (I have a UI tool that literally lets you drag and drop them) so I usually just commit these changes and then drag the commits around so it's not in the chain of when I want to send it out for review