Also if someone could help me understand: Are these so-called stacked commits not possible with multiple commits on a single branch? I prefer to write my commits as atomic, independent, related changes, on a single branch, with both Git and Mercurial. I am apparently missing something: why can't a better UI simply show a multi-change PR?
In the tool I wrote, you have a single branch with linear history. PRs in the chain are demarcated via commit messages. You then don't need any special rebase / sync commands -- you can use regular `git rebase -i` to reorder commits or edit a commit in the middle of a stack. Literally the only special command I need is "push this branch to github as multiple PRs".
Anyway I hope that alongside the branch-based you've built tool in `gh` that there will be an API that I can target.