2 files changed, 100 insertions, 8 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/transport.js b/packages/meshbay-hub/src/meshbay_hub/static/transport.js
index c200674..5ead80e 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/transport.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/transport.js
@@ -174,6 +174,18 @@ class MeshBayTransport {
         throw new Error('Node requires GEK proof but no crypto available');
       }
 
+      // Recorded the moment the challenge arrives, because everything below may
+      // need them — joining, in particular, happens before the proof and signs a
+      // transcript over both. Reading them further down, next to the proof that
+      // also uses them, meant join_request ran with neither.
+      //
+      // nonce_node ties a join to this connection, so one cannot be lifted onto
+      // another. node_pk is announced here because a first-time member has no
+      // GEK and so cannot complete the handshake that would prove it; it is
+      // unverified at this point and checked against the ack below.
+      this._nonceNode = window.MeshBayCrypto.b64decode(reply.nonce);
+      this.nodePk = reply.node_pk || null;
+
       // Recover session keys from node if not available locally (P2P keypair bundle)
       if (!this._sessionKeys && this._bundleKey && window.MeshBayKeys) {
         const kpResp = await this._sendAndWait({
@@ -258,14 +270,7 @@ class MeshBayTransport {
         _extractDtlsFingerprint(this._pc.localDescription.sdp),
         _extractDtlsFingerprint(this._rawAnswerSdp),
       );
-      const nonceNode = C.b64decode(reply.nonce);
-      // Kept for the life of the connection: a join_request is signed over it,
-      // which is what stops one being lifted onto another connection.
-      this._nonceNode = nonceNode;
-      // Announced in the challenge because joining needs it before the ack: a
-      // first-time member has no GEK, so they cannot complete the handshake that
-      // would prove this key. Unverified here; checked against the ack below.
-      this.nodePk = reply.node_pk || null;
+      const nonceNode = this._nonceNode;   // captured when the challenge arrived
       const gid = groupId || '';
 
       const proof = await C.handshakeProof(
diff --git a/packages/meshbay-hub/tests/test_spa_ordering.py b/packages/meshbay-hub/tests/test_spa_ordering.py
new file mode 100644
index 0000000..839698a
--- /dev/null
+++ b/packages/meshbay-hub/tests/test_spa_ordering.py
@@ -0,0 +1,87 @@
+"""
+Ordering guards for the SPA's connect() flow.
+
+These are source-level checks, which is not how one would normally test
+behaviour. They exist because a specific class of bug shipped to a live browser
+twice and no other test could see it: `connect()` is a long sequence in which
+later steps read values earlier steps set, and the Python end-to-end client in
+QE/deploy/ cannot catch a mistake there — it is a different implementation,
+written in the right order by construction, so it passes while the browser fails.
+
+Concretely: join_request signs a transcript over the node key and the node nonce,
+and runs *before* the GEK proof, because a first-time member has no GEK to prove.
+Both values were being read further down, next to the proof that also uses them,
+so every invited member hit "Handshake incomplete — reconnect and retry".
+
+If you restructure connect(), these will fail. Check the invariant still holds —
+that nothing reads a value assigned later — and then move the markers.
+"""
+
+from pathlib import Path
+
+import pytest
+
+STATIC = (Path(__file__).resolve().parents[1]
+          / "src" / "meshbay_hub" / "static")
+TRANSPORT = STATIC / "transport.js"
+
+pytestmark = pytest.mark.skipif(
+    not TRANSPORT.exists(), reason="SPA sources not present")
+
+
+def _positions(*needles: str) -> list[int]:
+    source = TRANSPORT.read_text()
+    out = []
+    for needle in needles:
+        idx = source.find(needle)
+        assert idx != -1, f"{needle!r} is gone from transport.js — update this test"
+        out.append(idx)
+    return out
+
+
+def test_challenge_values_are_captured_before_joining():
+    """
+    joinGroup() signs over node_pk and nonce_node, so both must be recorded when
+    the challenge arrives — not later, beside the proof.
+    """
+    # Deliberately loose markers: what matters is where the assignment happens,
+    # not how it is spelled, so a reordering fails on the ordering assertion
+    # below rather than on a missing string.
+    node_pk, nonce_node, join_call = _positions(
+        "this.nodePk = reply.node_pk",
+        "this._nonceNode = ",
+        "await this.joinGroup(",
+    )
+    assert node_pk < join_call, (
+        "node_pk is read from the challenge after joinGroup() runs — the join "
+        "would sign a transcript naming nothing")
+    assert nonce_node < join_call, (
+        "nonce_node is captured after joinGroup() runs — the join would not be "
+        "bound to this connection")
+
+
+def test_join_happens_before_the_gek_proof():
+    """
+    The whole point of joining in the pre-proof window: someone who has never
+    held the group key cannot produce a proof, so the key has to arrive first.
+    """
+    join_call, proof = _positions(
+        "await this.joinGroup(",
+        "await C.handshakeProof(",
+    )
+    assert join_call < proof, (
+        "the join must happen before the GEK proof — a first-time member has no "
+        "key to prove with")
+
+
+def test_the_ack_still_verifies_the_announced_node_key():
+    """
+    Taking node_pk from the challenge is only safe because the ack proves it and
+    the client compares the two. Losing that check would leave the announcement
+    trusted on its own.
+    """
+    source = TRANSPORT.read_text()
+    assert "Node identity changed during the handshake" in source, (
+        "the challenge's node_pk must be checked against the ack's")
+    assert "verifyNodeSignature" in source, (
+        "the ack's signature over the handshake transcript must still be verified")