That “just” is doing a LOT of work.
replyIt's already done on OpenBSD, and linux has the pieces to do it, though it's far more fragile and complicated. I'm not speaking hypothetically here, I've implemented code that works this way.
replyYou are minimizing the difference in scope between the audience and applications of OpenBSD and those of macOS.
replymacOS has had a capabilities model for over a decade called App Sandboxing. It would be entirely impractical to expect app authors to correctly declare their permissions up front and for users to audit them. Hence the permissions granted to sandboxed apps are pre-determined by the OS, and can be extended through explicit user interaction.
This is really hard to do in general
replyIt's done on the majority of the OpenBSD base system, as well as important ports like Chrome and Firefox. Linux also has the parts to do this, though it's more fragile and complicated.
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