- Random with constant-time-equal helper
- KEK loader from env (Tier 1) with InvalidKekError on bad/missing var
- AEAD via direct LibCrypto FFI bindings (Crystal 1.20 stdlib OpenSSL::Cipher
doesn't expose GCM auth_data/auth_tag, so we extend LibCrypto with
EVP_CIPHER_CTX_ctrl + EVP_aes_256_gcm and call them directly)
- Envelope: per-row DEK wrapped by KEK, AAD-bound, algorithm_id reserved
for crypto agility (0x01 = AES-256-GCM today, 0x02/0x03 reserved)
- 17 unit specs including a 100-iteration random property test
- Tag-tampered ciphertext / wrong-AAD / wrong-key all raise Aead::Error
4723716e08