Module keys 

Signing keys: the Signer trait (in-process Ed25519 now, KMS post-MVP) and an offline Keyring for verification with key rotation via key ids.

Structs

Ed25519Signer

In-process Ed25519 signer.

Keyring

Verification keyring: key id → public key. Old receipts stay verifiable after rotation as long as their key remains in the ring.

Enums

KeyError

Keyring / verification errors.

Traits

Signer

Abstract signer — the KMS integration point (brief Module G, post-MVP).