The point at which you _could_ start to have undefined behavior is within an `unsafe` block or function. So even if the "failure" occurred in some "safe" part of the code, the conditions to make that failure would start in the unsafe code.

When debugging, we care about where the assumptions we had were violated. Not where we observe a bad effect of these violated assumptions.

I think you get here yourself when you say:

> triggering undefined behavior can in theory cause the program to do anything, including fail spectacularly within seemingly unrelated safe code

The bug isn't where it failed spectacularly. It's where the C++ code triggered undefined behavior.

Put another way: if the undefined behavior _didn't_ cause a crash / corrupted data, the bug _still_ exists. We just haven't observed any bad effects from it.