Fix `show_envvar` output for a sequence or an empty `envvar`
The story of the bug "Fix `show_envvar` output for a sequence or an empty `envvar`" and how each model did on it.
Models fixed it in 5 of 6 recorded runs. The bug is in commit bb695aa of the repository's git history and the real fix is commit c53d373. A model gets the code at the first commit and the repository's own tests decide if it fixed the bug.