fix: an identity signs a named kind, and a device approval answers a request

The desktop main process builds every transcript itself from fields
(transcripts.js) and signs no raw bytes; the page's identity has the same
contract (crypto.js transcriptFor). The keyring seals no bundle while browser
access is off. On the node, device_add must redeem a pending request filed by
the same keys, and device_revoke is signed under its own prefix
(meshbay:device_revoke:v1), so a retirement signature admits nothing.

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

2 files changed, 20 insertions, 11 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/roster.py b/packages/meshbay-node/src/meshbay_node/roster.py
index 8144373..0116aaa 100644
--- a/packages/meshbay-node/src/meshbay_node/roster.py
+++ b/packages/meshbay-node/src/meshbay_node/roster.py
@@ -512,19 +512,22 @@ class Roster:
         await self._db.commit()
         return expires
 
-    async def take_device_request(self, code_hash: str,
-                                  user_id: str) -> dict | None:
+    async def take_device_request(self, code_hash: str, user_id: str,
+                                  pk_ed25519: str, pk_x25519: str) -> dict | None:
         """
-        Claim a pending request by its hash, for this account only.
+        Claim a pending request by its hash, for this account and these keys.
 
         Single use and scoped to the account: a request filed for one person
         cannot be redeemed by another even with the code, and a code that has
-        been spent is gone.
+        been spent is gone. Scoped to the keys too: the request is what the new
+        device filed and signed, so an approval redeeming it admits those keys
+        and no others.
         """
         assert self._db
         async with self._db.execute(
             "SELECT * FROM device_requests WHERE code_hash = ? AND user_id = ? "
-            "AND expires_at > ?", (code_hash, user_id, _now())
+            "AND pk_ed25519 = ? AND pk_x25519 = ? AND expires_at > ?",
+            (code_hash, user_id, pk_ed25519, pk_x25519, _now())
         ) as cur:
             row = await cur.fetchone()
         if row is None:
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 f94cade..20ebc79 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/admission.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/admission.py
@@ -20,6 +20,7 @@ from meshbay_common.device import (
     device_add_transcript,
     device_hello_transcript,
     device_request_transcript,
+    device_revoke_transcript,
 )
 from meshbay_common.join import JOIN_TTL, ROLE_MEMBER, ROLE_OPERATOR, join_transcript
 from meshbay_common.protocol import MNP
@@ -516,10 +517,17 @@ class AdmissionMixin:
 
         pk_ed_b64 = str(msg.get("pk_ed25519", ""))
         pk_x_b64 = str(msg.get("pk_x25519", ""))
+        code_hash = str(msg.get("code_hash", ""))
         ts = int(msg.get("ts", 0))
         if not (pk_ed_b64 and pk_x_b64):
             self._send({"type": "error", "detail": "Missing device keys"})
             return
+        # An approval answers a request the new device filed and signed with
+        # these keys. Without one, a countersignature alone — obtained however
+        # it was — would admit any key its holder chose.
+        if not code_hash:
+            self._send({"type": "error", "detail": "No pending request named"})
+            return
         if abs(time.time() - ts) > DEVICE_TTL:
             self._send({"type": "error", "detail": "Approval expired"})
             return
@@ -543,9 +551,8 @@ class AdmissionMixin:
 
         # Spend the request. Single use: an approval cannot be replayed, and a
         # code that was used is gone whatever else happens next.
-        code_hash = str(msg.get("code_hash", ""))
-        if code_hash and not await roster.take_device_request(
-                code_hash, self._user_id):
+        if not await roster.take_device_request(
+                code_hash, self._user_id, pk_ed_b64, pk_x_b64):
             self._send({"type": "error",
                         "detail": "That request is no longer pending"})
             return
@@ -696,10 +703,9 @@ class AdmissionMixin:
             self._send({"type": "error", "detail": "No such device"})
             return
 
-        transcript = device_add_transcript(
+        transcript = device_revoke_transcript(
             node_pk_b64=self._node_pk_b64(), user_id=self._user_id,
-            pk_ed25519_b64=target, pk_x25519_b64=victim["pk_x25519"],
-            nonce_node=self._nonce_node, ts=ts)
+            pk_ed25519_b64=target, nonce_node=self._nonce_node, ts=ts)
         signer = await self._verify_device_signer(roster, transcript,
                                                   msg.get("sig", ""))
         if signer is None: