> I'd say that's a mistake of the person who wrote the template then.
The fact that it's possible to make that mistake is basically the point! If "the whole point of concepts" were to "tell you what types you can successfully call it with" then that kind of mistake should not be possible.
It's true that there are certain cases where you know the full set of types you can use, but I'd argue that those are the less interesting/useful cases, anyways.
I'd say that's a mistake of the person who wrote the template then.
Also, there are Concepts where you absolutely know which types are allowed, e.g. std::same_as, std::integral, std::floating_point, etc.