Yes. It seems like running a capability-based system on top of a non-capability-based filesystem is a form of sandboxing. It's not impossible - for example, it'

Yes. It seems like running a capability-based system on top of a non-capability-based filesystem is a form of sandboxing. It's not impossible - for example, it's how filesystem API's work in a browser. But it's tricky to prevent sandbox escapes.