Matt Shumer named the pattern on X on July 28, 2026, three days after using an early version of it to have Claude Opus 5 build Claude of Duty, a from-scratch browser FPS judged blind against real Call of Duty footage. The published seed prompt tells the agent to fan out sub-agents per subsystem, /loop on each one, and route every result through a separate 'really harsh critic' sub-agent that blind-compares it to the reference and refuses to pass mediocre work. Shumer and the wider community have since applied the same builder-critic-blind-compare shape well beyond games — bug sweeps, legal-memo review, fantasy-draft optimization, and internal engineering overhauls — and it is a specific, named implementation of the broader loop engineering discipline rather than a separate concept. Its documented weak point: without a concrete external reference to judge against, the critic agent has nothing real to compare to and can invent arbitrary standards.