Add post-quantum remote auth key exchange

tests/test_auth.py

@@ -31,11 +31,12 @@ class TestGenerateKeypair:
 
 
 class TestCanonicalPayload:
-    def test_strips_pubkey_and_sig(self):
-        msg = {"command": "tabs.list", "id": "x", "pubkey": "abc", "sig": "def"}
+    def test_strips_auth_protocol_fields(self):
+        msg = {"command": "tabs.list", "id": "x", "pubkey": "abc", "sig": "def", "pq_kex": {"alg": "ML-KEM-768"}}
         data = json.loads(canonical_payload(msg))
         assert "pubkey" not in data
         assert "sig" not in data
+        assert "pq_kex" not in data
 
     def test_keys_sorted(self):
         msg = {"z": 1, "a": 2, "m": 3}
@@ -87,6 +88,15 @@ class TestSignVerify:
         other_nonce = bytes.fromhex(new_nonce())
         assert verify(pub_hex, other_nonce, msg, sig) is False
 
+    def test_post_quantum_shared_secret_is_bound_to_signature(self, keypair):
+        priv, pub_hex = keypair
+        nonce = bytes.fromhex(new_nonce())
+        msg = {"command": "tabs.list", "pq_kex": {"alg": "ML-KEM-768", "ciphertext": "abcd"}}
+        sig = sign(priv, nonce, msg, b"shared-secret").hex()
+        assert verify(pub_hex, nonce, msg, sig, b"shared-secret") is True
+        assert verify(pub_hex, nonce, msg, sig, b"other-secret") is False
+        assert verify(pub_hex, nonce, msg, sig) is False
+
     def test_garbage_pub_hex_returns_false_not_exception(self):
         assert verify("not-hex!!!!", b"nonce", {}, "00" * 64) is False