OK, but we can internally create new instance of digest but keep old Crypto.SHA256 instance (and reuse the worker). Keeping worker stored in Crypto would also work. We actually never have to terminate it if we reuse it that way.
So we agree to keep the worker and replace Digest instance internally when needed.
The question is do we allow reuse of Crypto.SHA256 or we need to create new one. If we choose the latter, we can still allow reuse of old one, or make it unuseable. I don't have a strong opinion. It's just esthetics.