1 files changed, 26 insertions, 0 deletions
diff --git a/packages/meshbay-common/tests/test_handshake.py b/packages/meshbay-common/tests/test_handshake.py
index ba8788a..8981db8 100644
--- a/packages/meshbay-common/tests/test_handshake.py
+++ b/packages/meshbay-common/tests/test_handshake.py
@@ -197,3 +197,29 @@ def test_transcript_is_unambiguous():
 def test_bindings_differ_by_transport():
     """A WebRTC proof must not be replayable on a QUIC connection."""
     assert webrtc_binding(b"\xaa" * 32, b"\xbb" * 32) != quic_binding(b"cert-der")
+
+
+def test_membership_refusal_carries_a_code_a_client_can_act_on():
+    """
+    `groups` is baked into the token at login, so someone added to a group after
+    signing in is refused although they are a member. The client refreshes and
+    retries on this code — it must not have to match on the human wording, which
+    is exactly the kind of coupling that breaks when someone improves a message.
+    """
+    import jwt as _jwt
+    from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
+    from cryptography.hazmat.primitives import serialization
+
+    sk = Ed25519PrivateKey.generate()
+    pem_priv = sk.private_bytes(
+        serialization.Encoding.PEM, serialization.PrivateFormat.PKCS8,
+        serialization.NoEncryption())
+    pem_pub = sk.public_key().public_bytes(
+        serialization.Encoding.PEM, serialization.PublicFormat.SubjectPublicKeyInfo)
+
+    token = _jwt.encode({"sub": "u1", "jti": "j1", "scope": "user", "groups": []},
+                        pem_priv, algorithm="EdDSA")
+
+    with pytest.raises(HandshakeError) as excinfo:
+        authorize_token(token, pem_pub, group_id="g" * 32)
+    assert excinfo.value.code == "not_a_member"