I just use the VS Code git integration with the jj colocated git repo. HEAD is @- and the changes in @ are considered working copy changes. It works for all I was using the VS Code integration for.

There are a number of jj plugins for vsc. VisualJJ and Jujutsu Kaizen are probably the two most popular

https://www.visualjj.com/

https://github.com/keanemind/jjk

You should be able to use the normal git gutter as long as your repository is colocated.

jjk or jjview

I have a PR up for jjk that does the full change as a review changes, and there's another user's PR that allows diffs over arbitrary ranges (i.e. when working out whether the commits that make up a PR are good as a whole rather than individually)

visualjj, it’s fantastic