If I were concerned about this threat vector I would put my SIM in a cheap throw away phone that has nothing installed on it and nothing of interest. I would back up my real phone to several devices and then FedEx (or equiv.) my phone to my destination if I planned to be there a while. I often used FedEx to ship things to data-center locations if I was going to be there for some time. I wore shorts and a t-shirt going through security.

Completely wiping all computing devices in advance every time you pass through a border checkpoint seems like the only defense against the government getting all of your personal data.

As we can see from the Tunic case, providing a "duress password" to cause data to be wiped on site when entered leaves you vulnerable to destruction of evidence charges, even if Tunic ultimately prevails.

What computing device vendors specialize in bulletproof, convenient wiping and restoration?

This can be solved by having a system in place with two passwords and partitions: assuming the phone is already locked, entering the second password unlocks a decoy phone account without anything incriminating, but at the same time encrypts or wipes the actual/main account. Entering first password unlocks the main account. The agent has no way of knowing if the first/second is being used.