Desktop operating systems have the capacity to do this; "server operating systems" (which are just desktop operating systems configured differently) already do this.

You run each program as a different user account. The HTTP daemon doesn't run as the same user as the DNS daemon even if they're on the same machine.

This is obviously annoying on a desktop because you have to use user switching to use another app. It would be better if desktop operating systems provided native support for it so that user accounts had a sub-account per app and apps automatically ran like that, and then a permission prompt if one app tries to access another app's files, which you can grant as one-time access or permanently.

Then you expect your email program to try to access a document you're attaching to an email, but if a video game tries to read your tax returns you can be appropriately suspicious.