The good news is: a judge can't hold you in contempt for relying on your Constitutional rights. So either it's going to be Constitutional for the state to demand encryption to be unlocked, or "indefinite" contempt detentions will be overturned by a superior court.

I have no problem with the state punishing someone for failing to provide something that has been deemed lawful to solicit, but failure to comply should result in another trial of some sort (possibly after a set period, so it's not immediate and abused). Based on the bill of rights, I believe you should not be detained indefinitely without a trial for the charges you are being held for, full stop. That the offense happened during a trial, and a judge was present is irrelevant. Otherwise, the charges you are being detained for have not had a trial by peer. Not to mention, you've now been denied a speedy and public trial. You could try to make a case that you've prevented your own speedy and public trial, but until there's been a conviction on whether you need to comply, I don't see how that reasoning is sustainable.

This is a good point, and someone should appeal this type of punishment without jury trial.

This is a very old legal debate. It can be resolved politically by passing statutes limiting the application of contempt rules, but that seems unlikely to happen soon.