This is actually a general problem with git and most cli tools, where it would be possible and useful to undo an action, but the tool developer cannot be bothered to implement such time-saving feature.
But to be clear: I’m the kind of person who runs git add .; that means I’m not maintaining a secret hidden third set of changes in the cache. I’m making changes in my working directory, and when those changes are in the shape I want them to be, I am staging all of those changes so I can commit all of those changes. If git add . overwrites a previous state of cached files, that’s fine - if I didn’t commit them I don’t want them.
Committing a codebase state that only exists in the cache and in your mind, on which you haven’t therefore run any build or test or linting tools because that precise set of changes has never existed in isolation in your codebase strikes me as requiring far too much mental powerlifting.
to unstage files you ran git add accidentally on
git reset