Ian Jackson [off-list ref] writes:

quoted

	if git rev-parse --verify -q "$1:$config"
	then
		die "fatal: tree contains $config: has been processed with new standalone (Rust) git-subtree; use that tool instead of this one.  See https://codeberg.org/diziet/git-subtree https://crates.io/crates/git-subtree"
	fi

Overly long output does not look very easy to read, but I kept it
the same as the original.

I'm not a great fan of the long error message myself, but it seemed to
be what the rest of the script was doing.  I didn't find any
multi-line calls to die, so that's why I did it this way.

I'm happy to reformat this to your taste.

Nah, it seems your plan is to deprecate this script over time and
move everybody to a newer implementation, so as long as "die" does
its job to stop and prevent breakages from spreading, that would be
fine.

Thanks.