It's a wetware protocol, not formal, mathematically certain concept. You also can never be certain that the car is not going to run through pedestrian crossing

It's a wetware protocol, not formal, mathematically certain concept. You also can never be certain that the car is not going to run through pedestrian crossing on red light when you step in - but it doesn't mean that traffic lights are useless. Semver is like traffic lights. For reproducible builds/increased certainty harden it with some kind of pinning or local copy.