2 files changed, 39 insertions, 1 deletions
diff --git a/packages/meshbay-common/src/meshbay_common/handshake.py b/packages/meshbay-common/src/meshbay_common/handshake.py
index 65b4e85..4d2cac2 100644
--- a/packages/meshbay-common/src/meshbay_common/handshake.py
+++ b/packages/meshbay-common/src/meshbay_common/handshake.py
@@ -278,7 +278,11 @@ def authorize_token(
         raise HandshakeError("Not a member of this group", code="not_a_member")
 
     if hosted_groups is not None and group_id not in hosted_groups:
-        raise HandshakeError("Group not hosted on this node")
+        # Coded, because a client handed several nodes for one group has to tell
+        # "this node cannot serve it, try the next one" apart from "you, in this
+        # browser, must do something first". Uncoded it was neither, and a node
+        # wrongly registered for a group took that group down for everyone.
+        raise HandshakeError("Group not hosted on this node", code="not_hosted")
 
     return AuthorizedPeer(
         user_id=user_id,
diff --git a/packages/meshbay-common/tests/test_handshake.py b/packages/meshbay-common/tests/test_handshake.py
index 8981db8..d4f6d2b 100644
--- a/packages/meshbay-common/tests/test_handshake.py
+++ b/packages/meshbay-common/tests/test_handshake.py
@@ -223,3 +223,37 @@ def test_membership_refusal_carries_a_code_a_client_can_act_on():
     with pytest.raises(HandshakeError) as excinfo:
         authorize_token(token, pem_pub, group_id="g" * 32)
     assert excinfo.value.code == "not_a_member"
+
+
+def test_a_group_this_node_does_not_host_is_refused_with_a_code():
+    """
+    A client is handed every node the hub registered for a group, and only some
+    of them may be able to serve it. Telling "try the next node" apart from
+    "you, here, must do something first" is what this code is for: without it
+    the client either stopped at the first refusal — which is how a group went
+    dark on 2026-09-11 with its real host online — or had to match on wording.
+    """
+    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)
+
+    group = "g" * 32
+    token = _jwt.encode(
+        {"sub": "u1", "jti": "j1", "scope": "user", "groups": [group]},
+        pem_priv, algorithm="EdDSA")
+
+    # A member of the group, on a node that does not host it.
+    with pytest.raises(HandshakeError) as excinfo:
+        authorize_token(token, pem_pub, group_id=group, hosted_groups={"other"})
+    assert excinfo.value.code == "not_hosted"
+
+    # And the node that does host it still lets them in.
+    peer = authorize_token(token, pem_pub, group_id=group, hosted_groups={group})
+    assert peer.group_id == group