feat(node): accept a device link request before the proof (MNP 6.3)

A new device of a known account holds no identity the node pinned, so it
cannot complete a handshake until a pinned device approves it: it now files
device_add_request in the pre-proof window, as the desktop app's case
already required. The request stays inert until countersigned; at most 10
are pending per account, the oldest dropped. A 6.2 node answers it
"Handshake required", which a client reads as "cannot link here".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2 files changed, 21 insertions, 10 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/admission.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/admission.py
index fd9c756..baa8001 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/admission.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/admission.py
@@ -404,12 +404,16 @@ class AdmissionMixin:
         """
         A new device files itself as pending, bound to a code it displays.
 
-        Served in the pre-proof window: by construction the caller holds no key
-        this node knows, so there is nothing yet to prove. Filing is inert —
-        nothing is admitted until an existing device countersigns.
+        Served in the pre-proof window as well as after it: by construction the
+        caller holds no key this node knows, so it cannot prove the group key —
+        filing is what will give it one. The account is the token's, which the
+        node authorized before issuing the challenge. Filing is inert — nothing
+        is admitted until an existing device countersigns.
         """
         roster = self._ctx.get("roster")
-        if roster is None or not self._user_id or not self._nonce_node:
+        user_id = self._user_id or getattr(self, "_pending_sub", None)
+        username = self._username or getattr(self, "_pending_username", "") or ""
+        if roster is None or not user_id or not self._nonce_node:
             self._send({"type": "error", "detail": "Not ready for a device request"})
             return
 
@@ -426,7 +430,7 @@ class AdmissionMixin:
         # The account must already be known here. Anti-spam rather than a
         # security boundary: the filing key is unpinned by construction, so this
         # bounds the table, not the trust.
-        existing = await roster.list_devices(self._user_id)
+        existing = await roster.list_devices(user_id)
         if not existing:
             self._send({"type": "error",
                         "detail": "This account has no device on this node yet — "
@@ -444,7 +448,7 @@ class AdmissionMixin:
             return
 
         transcript = device_request_transcript(
-            node_pk_b64=self._node_pk_b64(), user_id=self._user_id,
+            node_pk_b64=self._node_pk_b64(), user_id=user_id,
             pk_ed25519_b64=pk_ed_b64, pk_x25519_b64=pk_x_b64,
             code_hash=code_hash, nonce_node=self._nonce_node, ts=ts)
         try:
@@ -461,11 +465,11 @@ class AdmissionMixin:
 
         ttl = int(self._ctx.get("device_request_ttl") or 3600)
         expires = await roster.file_device_request(
-            user_id=self._user_id, username=self._username or "",
+            user_id=user_id, username=username,
             pk_ed25519=pk_ed_b64, pk_x25519=pk_x_b64,
             code_hash=code_hash, ttl=ttl)
-        self._audit("device_request", f"{pk_ed_b64[:16]}")
-        log.info("Device request filed for %s (%s)", self._user_id[:8],
+        self._audit_join("device_request", f"{pk_ed_b64[:16]}")
+        log.info("Device request filed for %s (%s)", user_id[:8],
                  pk_ed_b64[:16])
         self._send({"type": MNP.DEVICE_REQUEST_ACK, "v": MNP_VERSION,
                     "expires_at": expires})
@@ -761,7 +765,8 @@ class AdmissionMixin:
         """
         self._device_attempts = getattr(self, "_device_attempts", 0) + 1
         if self._device_attempts > 5:
-            self._audit("device_attempts_exceeded", str(self._device_attempts))
+            # _audit_join: a device request may be filed before the proof.
+            self._audit_join("device_attempts_exceeded", str(self._device_attempts))
             self._send({"type": "error",
                         "detail": "Too many device attempts on this connection"})
             return False
diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py
index 0ceefb5..7452f42 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py
@@ -120,6 +120,12 @@ class DispatchMixin:
                     self._spawn(self._do_gek_bundle_fetch())
                 else:
                     self._spawn(self._do_keypair_bundle_fetch())
+            elif mtype == MNP.DEVICE_REQUEST and self._gek_challenge is not None:
+                # A machine with no key on this node cannot prove the group key —
+                # filing is how it gets one. Inert: nothing is admitted until a
+                # device already pinned countersigns, the code is bound to the
+                # keys, and the device budget bounds it (MNP 6.3).
+                self._spawn(self._do_device_request(msg))
             elif mtype == MNP.JOIN_REQUEST and self._nonce_node:
                 # Valid both before the GEK proof (a new member has no GEK to prove
                 # with) and after it (an operator pairing a browser is already