The government would never prosecute a company for fraud where that fraud consists of cooperating with the government after promising to a suspected criminal that they wouldn't.

That's not the scenario I was thinking of. There are other possibilities here, like providing a decryption key (even if by accident) to a criminal who's stolen a business's laptop, or if a business had made contractual promises to their customers, based on Apple's promises to them. The actions would be private (civil) ones, not criminal fraud prosecution.

Besides, Apple's lawyers aren't stupid enough to forget to carve out a law-enforcement demand exception.