The enforcement does not necessarily need to come from the compiler - it's not uncommon to introduce additional required processes / checks that new code needs

The enforcement does not necessarily need to come from the compiler - it's not uncommon to introduce additional required processes / checks that new code needs to pass (ex. "tests need to pass", "at least one reviewer must approve a change"). The compiler probably won't be able to leverage those annotations since there's always a potential for mismatch between annotations and code (but the verification system should be able to catch it) - I agree that integration into the language would be needed here, but that's not likely going to happen with C/C++ so I'm open to using a solution that's not perfect. :-)