The Reviewer Needed a Map, Not More Territory

The July 10 GitHub engineering account offers an unusually concrete lesson in agent design. Moving Copilot code review onto shared grep, glob, and view tools initially raised cost and reduced useful findings because the reviewer began exploring repositories like a general coding assistant. GitHub then rewrote the workflow to start from the diff, form narrow questions, batch discovery, and read only the evidence required. The company reports roughly 20 percent lower average review cost than the control without a quality signal that blocked shipping. Those figures come from the internal production comparison, but the traced failure mode is the durable point: the same tool surface can produce different behavior when its instructions imply a different job.