pub fn decode(shared_secret: &[u8], packet: &KkPacket) -> Result<Vec<u8>>Expand description
Decode a KK packet back to plaintext.
The receiver uses:
- The shared secret (what both parties know)
- The entropy snapshot ε (transmitted with the packet)
- Deterministic derivation (same HKDF, same inputs = same keys)
Same universe, same moment reference, same symbol values.