New framework proposes three-part harness to keep AI agent loops from drifting

A developer builder describes a shift from simple test-pass/fail agent loops to a more structured 'harness' architecture for autonomous coding agents. The design separates a development agent that modifies a feature, a product agent that only sees what a real user would see, a behavior driver that simulates real requests, and a scorer/controller that identifies the next capability gap to fix, with repository state carrying lessons between sessions.