tdd-first

Enforce a RED→GREEN→REFACTOR cycle for a feature. Writes failing tests BEFORE implementation, runs the test suite to confirm the red state, then invokes the implementer agent with the failing tests as authoritative input, then re-runs to confirm green. Use when: user says /tdd-first, 'do this test-first', 'TDD this feature', or before any safety-critical / migration / auth path change. Default for changes under any root named by the safety-critical.roots slot of .claude/project-profile.md, and anything touching a live external-action path.