`make try` ran against a fixed directory on one person's machine. It
failed for anyone else, and where that directory existed it rewrote the
checksum attributes and modification times of real files.
It now writes three small files into a new directory from `mktemp -d`,
runs the same sequence of commands on it, and removes it with an EXIT
trap. All steps run in one shell, so the trap also removes the
directory when a step fails.
`TODO.md`: the `try` sentence leaves Next Step and is recorded under
Completed Steps.
Model: opus-5-5
sneak