[darrenf]

> Clearly the correct way to implement this is to run each command in a short-lived container and check the output matches what's expected.

I'm not sure it is clearly correct. Some commands don't produce output, `mkdir` and `cd` for example (the first two in the animation). Furthermore they'd have to blacklist `echo` and other ways to produce the output against the spirit of the exercise... until an answer is, say, `echo $?` - at which point you'd require a preceding command exiting in a suitable way in order to keep the "just execute it" approach workable.