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>

1 files changed, 25 insertions, 0 deletions

diff --git a/packages/meshbay-common/src/meshbay_common/device.py b/packages/meshbay-common/src/meshbay_common/device.py
index 3a598d0..2d6747f 100644
--- a/packages/meshbay-common/src/meshbay_common/device.py
+++ b/packages/meshbay-common/src/meshbay_common/device.py
@@ -37,6 +37,7 @@ import hashlib
 DEVICE_REQUEST_PREFIX = b"meshbay:device_req:v1"
 DEVICE_ADD_PREFIX = b"meshbay:device_add:v1"
 DEVICE_HELLO_PREFIX = b"meshbay:device_hello:v1"
+DEVICE_REVOKE_PREFIX = b"meshbay:device_revoke:v1"
 
 # Same as the join and admin transcripts: interactive exchanges that complete in
 # milliseconds, so anything older is a replay.
@@ -126,6 +127,30 @@ def device_add_transcript(
     ])
 
 
+def device_revoke_transcript(
+    node_pk_b64: str,
+    user_id: str,
+    pk_ed25519_b64: str,
+    nonce_node: bytes,
+    ts: int,
+) -> bytes:
+    """
+    Signed by a pinned device, retiring one of the account's devices.
+
+    A prefix of its own, never the admission transcript: a signature given to
+    retire a key would otherwise admit that same key on a node where it is not
+    pinned yet, and whoever asks a device to sign a retirement could turn it
+    into an addition.
+    """
+    return _pack(DEVICE_REVOKE_PREFIX, [
+        node_pk_b64.encode(),
+        user_id.encode(),
+        pk_ed25519_b64.encode(),
+        nonce_node,
+        str(ts).encode(),
+    ])
+
+
 def device_hello_transcript(
     node_pk_b64: str,
     group_id: str,