Ok? A debugger also wouldn’t help the hardest bug I ever fixed!

It is not the only tool in the bag. But literally the first question anyone should ask when dealing with any bug is “would attaching a debugger be helpful?”. Literally everyone who doesn’t use a debugger is less effective at their jobs than if they frequently used a debugger.

A modern debugger would have made that trivial. Just turn on time travel debugging mode and you would have been done after the first time it occurred.

Wait until the memory is corrupted and causes a crash. Set a hardware breakpoint on the corrupted memory location and run backward until the memory location was written in the signal handler. Problem solved.

Memory corruption bugs in single-threaded code are a solved problem.