Trying to add someone to page restrictions who is not in space permissions should raise an error

We carefully manage who has the ability restrict pages. But even many of these who genuinely need this ability, struggle to understand/remember how page restrictions only narrow down from space permissions. As Confluence Administrator, one of my most common user-issues results from pages restricted to individuals who don't have access to the space (whether view or edit).

It would be really helpful, if this were the behaviour when that happened:

1. Someone with restrict permissions tries to add an individual to page restrictions to edit who doesn't have edit rights in the space (or view)
2. An error pops up stating: you must add this individual to the space permissions in order for this restriction to work
3. Provides a link to space permissions and/or offers to send a notice to the space administrator (like when requesting access)
4. Doesn't allow that person to be added until it is fixed