Of course unsigned is defined. That's besides the point. The point is: how often in your code, do you expect 1 minus 2 to equal a very large number, vs. the number -1.

both seem equally undesirable to me in all cases where I intend neither. though one also risks undefined behavior, so that is strictly worse.

the reason I use a type system is to make error classes unrepresentable (where possible) or a failure. these are both leaky abstractions in the worst possible manifestation: silent misbehavior at runtime.