Contract for the custom UDP transport (v2):
- aura-crypto: AeadKey — ChaCha20-Poly1305 with an EXPLICIT per-message nonce
(caller passes the counter), for datagram transports where packets may be lost
or reordered. AeadSession::into_parts() hands off (AeadKey, counter). Same
nonce scheme as AeadSession, so they interoperate on one key with disjoint
counter ranges. +4 tests.
- aura-proto: DatagramSender/DatagramReceiver (record = seq(8) || AEAD(frame,
aad=seq), sliding replay window) and Session::into_datagram_parts(); reuse for
a UDP data path. +1 test. Existing 16 crypto / 13 proto tests still green.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>