playlists: make the writes actually leave the browser

Reported from a phone: signing in with the same account showed no
playlists. syncWith was called from exactly one place in the interface,
so creating a playlist, deleting one, removing a track and saving the
queue all wrote to IndexedDB and stopped there. The store pushes itself
now, coalesced, so a new mutation cannot forget to.

Silence was the real defect. The node audited only successes, so a
refusal left no trace and user_blob_list none at all; the background
push swallowed its reason; the interface said nothing. All three report
now, and "Sync now" says what happened either way.

An unreadable blob on a node was treated as a fetch failure and returned
before the push — permanent, once the node held anything. It is an
absence: the client is the authority, and it gets overwritten.

A sign-in reconciles whatever this browser already holds, a pending push
is flushed when the page goes away, and a push that did not land is
retried once.

no_key is spelled out: a client that signs in with its remembered device
key only ever has a bundle key persisted before the playlist subkey
existed, and an AES handle is non-extractable.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

2 files changed, 51 insertions, 8 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc_server.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc_server.py
index 298b3cd..99ba3c9 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc_server.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc_server.py
@@ -1178,11 +1178,23 @@ class WebRTCPeerSession:
     # `user_id` in the body would let any member of this group read or
     # overwrite any other member's blob, which is finding C5 one size down.
 
+    def _user_blob_refuse(self, detail: str, kind: str = "") -> None:
+        """
+        Refuse, and say so in the audit log.
+
+        A refusal used to be invisible here: the audit line was written only
+        after a store *succeeded*, so a client whose writes were all being
+        turned away looked exactly like a client that never wrote — which is
+        how a wedged sync went unnoticed for two hours.
+        """
+        self._audit("user_blob_refused", f"{kind} {detail}".strip())
+        self._send({"type": "error", "detail": detail})
+
     def _user_blob_kind(self, msg: dict) -> str | None:
         """The validated `kind`, or None having already refused."""
         kind = msg.get("kind")
         if not isinstance(kind, str) or not _USER_BLOB_KIND_RE.match(kind):
-            self._send({"type": "error", "detail": "Unknown blob kind"})
+            self._user_blob_refuse("Unknown blob kind", str(kind)[:40])
             return None
         return kind
 
@@ -1206,13 +1218,13 @@ class WebRTCPeerSession:
 
         blob = msg.get("blob_enc")
         if not isinstance(blob, (bytes, bytearray)) or not blob:
-            self._send({"type": "error", "detail": "Missing blob_enc"})
+            self._user_blob_refuse("Missing blob_enc", kind)
             return
         blob = bytes(blob)
 
         rev = msg.get("rev")
         if not isinstance(rev, int) or rev < 0:
-            self._send({"type": "error", "detail": "Missing rev"})
+            self._user_blob_refuse("Missing rev", kind)
             return
 
         limit = (USER_BLOB_MANIFEST_MAX if kind == "playlists"
@@ -1221,8 +1233,7 @@ class WebRTCPeerSession:
             # A stated reason, not a bare error: the client turns this into a
             # sentence the reader can act on ("this playlist is too large"),
             # and a refusal nobody can read is a support case.
-            self._send({"type": "error",
-                        "detail": f"Blob too large ({len(blob)} > {limit})"})
+            self._user_blob_refuse(f"Blob too large ({len(blob)} > {limit})", kind)
             return
 
         # What the account already uses, minus whatever this call replaces.
@@ -1231,9 +1242,9 @@ class WebRTCPeerSession:
         if existing:
             used -= len(existing["blob_enc"])
         if used + len(blob) > USER_BLOB_ACCOUNT_MAX:
-            self._send({"type": "error",
-                        "detail": f"Account blob quota exceeded "
-                                  f"({used + len(blob)} > {USER_BLOB_ACCOUNT_MAX})"})
+            self._user_blob_refuse(
+                f"Account blob quota exceeded "
+                f"({used + len(blob)} > {USER_BLOB_ACCOUNT_MAX})", kind)
             return
 
         await store.store_user_blob(self._user_id, kind, rev, blob)
@@ -1263,6 +1274,7 @@ class WebRTCPeerSession:
         if not store:
             return
         blobs = await store.list_user_blobs(self._user_id)
+        self._audit("user_blob_list", f"{len(blobs)} blobs")
         self._send({"type": MNP.USER_BLOB_LIST_RESP, "v": MNP_VERSION,
                     "blobs": blobs})
 
diff --git a/packages/meshbay-node/tests/test_user_blob_mnp.py b/packages/meshbay-node/tests/test_user_blob_mnp.py
index 296239f..85893af 100644
--- a/packages/meshbay-node/tests/test_user_blob_mnp.py
+++ b/packages/meshbay-node/tests/test_user_blob_mnp.py
@@ -242,6 +242,37 @@ async def test_an_unauthenticated_session_reaches_nothing(store):
 
 
 @pytest.mark.asyncio
+@pytest.mark.parametrize("msg, why", [
+    ({"kind": "nonsense", "rev": 1, "blob_enc": b"x"}, "Unknown blob kind"),
+    ({"kind": "playlists", "rev": 1}, "Missing blob_enc"),
+    ({"kind": "playlists", "blob_enc": b"x"}, "Missing rev"),
+    ({"kind": "playlists", "rev": 1,
+      "blob_enc": b"x" * (USER_BLOB_MANIFEST_MAX + 1)}, "too large"),
+])
+async def test_a_refusal_is_audited_and_not_merely_sent(store, msg, why):
+    """A refusal used to leave no trace at all: the audit line was written only
+    after a store *succeeded*. So a client whose every write was being turned
+    away looked exactly like a client that never wrote — which is how a wedged
+    sync went unnoticed, with the operator's own log saying nothing."""
+    s = _session(store)
+    await s._do_user_blob_store(msg)
+    assert _last(s)["type"] == "error"
+    events = [(e, d) for e, d in s.audited if e == "user_blob_refused"]
+    assert events, "the refusal is invisible in the audit log"
+    assert why in events[0][1]
+
+
+@pytest.mark.asyncio
+async def test_a_listing_is_audited(store):
+    """Half the traffic was invisible: `user_blob_list` is what every sync does
+    first, and it wrote no audit line, so the log could not distinguish a client
+    that was syncing from one that was not."""
+    s = _session(store)
+    await s._do_user_blob_list()
+    assert ("user_blob_list", "0 blobs") in s.audited
+
+
+@pytest.mark.asyncio
 async def test_reads_and_writes_are_audited(store):
     """The node logs that a blob moved, never what was in it — the same line
     `keypair_bundle_store` already writes."""