If you want to exit with a specific error code, the way to do that currently is to throw an ExitCode error or pass one to MyCommand.exit(with:). Neither of these will print anything, so you'd want to print any error message to stderr first.
You created that issue 6 hours ago. I wrote that message yesterday before continuing to come up with a solution for the rest of the night. I swear I looked before writing the message. Clearly not before posting.
I'll see if I cannot implement that feature since it is marked as a starter.
Also, obviously coincidences and all that... but that's some crazy timing.