Implement It Twice on Purpose — a Cross-AI Differential Harness That Finds the Hole in Your Own Spec

What you'll do

A differential verification harness you own for one money-critical business rule: a written specification with an explicit list of what it does not yet decide, a hand-computed golden table that outranks every AI in the project, two independent implementations produced from that specification by AI systems from different companies with no sight of each other, a pinned no-network sandbox both run inside, a property-based generator whose input domain comes from the specification and whose coverage of your named edge cases is asserted rather than assumed, a triage rule that resolves every disagreement against your specification instead of against a model's opinion, a permanent frozen corpus of every counterexample ever found, a set of invariant properties that catch the failures differential testing is structurally blind to, and an append-only ledger recording which tool produced which implementation, under which specification version, and who decided what correct meant.