> which indicates the undefined behavior actually helps rather than hurts when used with good tooling

No, one doesn't need undefined behavior for that at all (which does hurt).

What actually helps is diagnosing the issue, just like one can diagnose the unsigned case just fine (which is not UB).

Instead, for this sort of thing, C could have "Erroneous Behavior", like Rust has (C++ also added it, recently).

Of course, existing ambiguous C code will remain to be tricky. What matters, after all, is having ways to express what we are expecting in the source code, so that a reader (whether tooling, humans or LLMs) can rely on that.