Stop Reading AI Code. Start Measuring It. (A Rails Playbook.)

A practical Rails playbook for automating code quality gates on AI-generated code. The author builds a single `bin/rake quality` command that enforces five metrics: line and branch test coverage (via SimpleCov), cyclomatic complexity and ABC size (via RuboCop and Flog), module size as an SRP proxy, and mutation testing kill ratio (via Mutant). Each metric includes the Ruby implementation, threshold rationale, and honest caveats. A ratchet mechanism prevents mutation score regressions without requiring an upfront investment. The post argues that AI coding agents make previously-annoying complexity cops viable because the agent can fix violations automatically, shifting human review toward intent and architecture rather than mechanical correctness.