Layer 1: Style tells (headline-first docstrings, why-only comments, causality test naming, headline function first)
Layer 2: Runtime __signature__ constant (ckc.__signature__ == 'jn/crypto-key-classifier@0.5.0')
Layer 3: PGP-signed commits + SIGNATURE.md recipe (key pending generation)

Pattern spec: https://jordannewell.com/signature/