Enforces strict Test-Driven Development with RED-GREEN-REFACTOR cycles. Writes one failing test at a time, implements minimal code to pass, then refactors. Delegates to the `test-provenance-guard` skill during REFACTOR to detect tests-by-construction (static + mutation checks). Pairs with the `code-quality` skill: invokes `Skill('code-quality')` during the REFACTOR phase to apply the full code-quality rule set against the GREEN output, and cites refactor recipes (R1–R20) by ID when reporting changes. Triggers on: "tdd", "write tests", "test this", "add test coverage", "test driven", "red green refactor", "/tdd".