so just for understanding: repeated `git add -p` followed by a `git commit` turns into repeated `jj split; jj squash`, since you create a commit each time?
That would work, yes, but there's also `jj squash -i` to move part of the child commit into the parent. There's also the more generic `jj move` command for moving part of any commit into any other commit (ancestor, descendant, sibling), so you `jj squash -i` is equivalent to `jj move -i --from @ --to @-` (where `@` is syntax for the working copy commit and `@-` is syntax for its parents).
`jj split -r <commit>`, where `<commit>` may be the working copy commit (which is the default). See https://github.com/martinvonz/jj/blob/main/docs/git-comparis... for more examples.