If you're writing unsafe code meant to be used by safe code, the safety boundary is usually at the interface level (i.e. public functions not marked unsafe), no

If you're writing unsafe code meant to be used by safe code, the safety boundary is usually at the interface level (i.e. public functions not marked unsafe), not necessarily just the unsafe {} construct. So there's 'safe code' that only uses safe interfaces and should be memory safe whatever it does, there's unsafe code which explicitly opts into the unsafe operations where memory safety issues can occur, and code in the middle which is not marked unsafe but still needs to uphold invariants the unsafe code depends on. As a rule of thumb if you've got unsafe in library code, the entire module (which is the public/private boundary) may have an impact on safety.