How does Meteor determine prodOnly?

How does Meteor know if the built app is running in production or not?

What exactly determines if prodOnly packages get run?

If you are running meteor with the --production flag (which you shouldn’t do for production)
or if you are running a built version of the app

That’s what I thought. Is there any reason why a built version would not use prodOnly packages?

Good question! I don’t use prodOnly packages very often so haven’t run into this problem before