No secret witness
This project's own term (not standard industry vocabulary) for a specific design choice: the program and its inputs are entirely public, so the verifier can re-execute the program itself and knows the correct value of almost every trace column in advance — turning most of what would need an algebraic gadget elsewhere into a direct boundary assertion.
In this repo: the reason branch outcomes and register selectors don't need an is-zero/lookup gadget. Full argument: Why This zkVM's Soundness Doesn't Need a Lookup Argument.