Cleaner msg struct naming.

tests/test_sansio.py

@@ -7,7 +7,7 @@ from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PublicKey
 from quantumpipe.chab3 import encrypt
 from quantumpipe.exceptions import ProtocolError
 from quantumpipe.handshake import (
-    _MSG1_REGISTER,
+    REG_MSG1,
     _fresh_ephemeral,
     _public_from_idroot,
     _x25519_private_key,
@@ -696,7 +696,7 @@ def test_mitm_reused_reveal_detected(psk):
     hs = m_out._exchange
     hs._reveal = r_a
     hs._eph_m, hs._ephemeral, e_m, e_x = _fresh_ephemeral()
-    body = _MSG1_REGISTER.pack(e_m, e_x, kdf("commit", e_m, e_x, r_a))
+    body = REG_MSG1.pack(e_m, e_x, kdf("commit", e_m, e_x, r_a))
     msg1m = bytes(encrypt(body, key=kdf("reg/msg1", psk), ad=b""))
     hs._chain.advance(msg1m)  # startA was bypassed: advance the chain
     (m2b,) = b(msg1m)