The sane way to do it would be to have something like `git stage` and `git unstage`, as distinct single-purpose commands.

The first example at https://git-scm.com/book/en/v2/Git-Basics-Git-Aliases is literally exactly what you want.

"It's easy to make the CLI less bad, but the developers have never bothered to do so themselves" is reinforcement of my complaint, not dismissal of it.

Not trying to dismiss, just assist ;)