pub fn decrypt_packet(
packet: &Packet,
card: &MailboxCard,
key: &MailEncryptionKey,
owner: &AgentId,
now: i64,
) -> Result<Letter>Expand description
Stateless authenticated opening of a historical packet. This verifies shape,
cryptography and future skew; callers must enforce new-acceptance expiry and
durable deduplication (MailInbox implements those state transitions).