A single RFC 8617 §5.1.1 hardening fix on the verify path: the ARC-Message-Signature must sign the From header. The public API (Seal, Verify, SealOptions, SealResult) is unchanged.
Fixed
- Verify now requires the ARC-Message-Signature to sign the From header (RFC 8617 §5.1.1); a chain whose AMS
h=omits From is treated as cv=fail (#31).