> Probably some arcane git magic to (interactively) rebase branch

There is not really a command for that yet, short of adding a bunch of `exec` steps to your interactive rebase manually. See https://news.ycombinator.com/item?id=32217204 for an upcoming command.

You might enjoy using https://github.com/gitext-rs/git-stack, which specifically tries to let you manage stacked branches locally while not exposing tons of PRs to your coworkers.

git-branchless itself also lets you manage stacked branches in various ways. For example, you can do `git checkout <branch>`, `git commit --amend`, and then `git restack` to rebase all the descendant branches sensibly. You can use it on the local side of things only and then use Github PRs as normal.