Throw (using provided error message) if expression is false.
insist(expr)`custom error message`;
If expr is falsy, then the template contents are reported to the console and also in a thrown error.
The literal portions of the template are assumed non-sensitive, as are the typeof types of the substitution values. These are assembles into the thrown error message. The actual contents of the substitution values are assumed sensitive, to be revealed to the console only. We assume only the virtual platform's owner can read what is written to the console, where the owner is in a privileged position over computation running on that platform.