Fuchsia does a pure capability model, and resources, even as basic as the file system are provided through handles - and your file system handle is a handle to

Fuchsia does a pure capability model, and resources, even as basic as the file system are provided through handles - and your file system handle is a handle to what would be a directory elsewhere, but that is the entire file system so it’s not a matter of finding a traversal exploit. In principle you could do something similar with the Mac/iOS sandbox by starting a process with a compute only sandbox, and then provide it with specific sandbox entitlements (from the parent) which includes specific file systems, however they still in principle can see a full version of the fs. And yeah, any OS that isn’t completely new is burdened with support for old apps, but then iOS which used its newness to have a stronger base security model is constantly beaten up for that model.