[autoexec]

What's the real-life case where hello world fails because the file system is full?

You could do all kinds of things that would cause hello world to "fail". A broken monitor (or even one unplugged) wouldn't show "hello world" or give any indication of an error too, but it's hardly the codes fault. The code does what it's supposed to and ignores all kinds of other things that could go horribly wrong. That's not really a bug, just a known and expected limitation of the program's scope.

[oneeyedpigeon]

As I said, not hello world necessarily, but any program that writes output can encounter this problem, and there's an overlap with general file-writing even.