The security barrier must be earlier. It will make everything easier to secure.
By analogy, it's like securing your own house. You can lock points of entry to your house, and it'll work fine for the entire house. But if you move the security barrier to wrong place because you assume burglars may freely roam inside your house, you'll end up with locks on your bathroom, padlocks on your drawers, gates on your bed, TV stored in a safe, and kitchen utensils chained to walls.
Here, your OS is your house. If you work with assumption that you let malware in, and running viruses is normal part of Rust development, you'll need extraordinary level of sandboxing paranoia similar to having things in your house chained to walls. It's going to be incredibly hard to secure everything, and it's going to be incredibly inconvenient to use the language that has to act at all times as if all your code was infected and dangerous.