I’ve really been loving these two neovim JJ plugins
For splitting commits: https://github.com/julienvincent/hunk.nvim
For resolving conflicts: https://github.com/rafikdraoui/jj-diffconflicts
And, you're right, it's powers largely come from the underlying jj - it mostly just runs jj commands behind the scenes, parses the output, and displays it. But it's all so beautiful, seamless etc..
I can't wait to really dig into the big additions released yesterday in v0.9.0 - themes, vim-like leader key shortcuts, other shortcuts etc...
There is also lazyjj as an interactive UI.
Note for other readers: jj also has a literal `jj absorb` command. That one does what you'd expect from mercurial, i.e. moves diffs from the current commit into the most recent ancestral commit where that file was changed.
You name them with bookmarks which are sort of like branch names except they don't follow along automatically as you make new revisions. You can point an existing bookmark at a later revision when you're ready to push new changes.