feat: bundles sealed per node under the passphrase and the hub's pepper

The session key is M = HKDF(Argon2(passphrase) || pepper, account id); each
node's bundle key and the playlist key derive from it. Bundles are MBK3, bound
to account and node; MBK1/MBK2 are refused by name, never replaced silently.
Playlists move to key v2 and are re-sealed over unreadable node copies.

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

1 files changed, 15 insertions, 6 deletions

diff --git a/packages/meshbay-hub/tests/test_playlist_store.py b/packages/meshbay-hub/tests/test_playlist_store.py
index 701de41..3c1d109 100644
--- a/packages/meshbay-hub/tests/test_playlist_store.py
+++ b/packages/meshbay-hub/tests/test_playlist_store.py
@@ -272,16 +272,25 @@ def test_a_node_holding_something_unreadable_does_not_wedge_the_sync(steps):
     assert "Depuis le menu" in s["names"]
 
 
-def test_a_session_from_before_the_hkdf_handle_degrades_rather_than_failing(steps):
-    """A bundle key loaded out of IndexedDB from before `deriveBundleKeys`
-    existed has no HKDF handle, and the passphrase is not in memory to
-    re-derive from. Playlists stay local until the next sign-in — reported,
-    rather than silently doing nothing."""
-    r = steps["a session from before the HKDF handle"]["result"]
+def test_a_session_from_before_the_pepper_degrades_rather_than_failing(steps):
+    """A bundle key from before the pepper opens nothing, and the passphrase
+    is not in memory to re-derive from. Playlists stay local until it is
+    entered again — reported, rather than silently doing nothing."""
+    r = steps["a session from before the pepper"]["result"]
     assert r["ok"] is False and r["reason"] == "no_key"
     assert r["pushed"] == 0
 
 
+def test_a_node_sealed_under_the_previous_key_is_sealed_again(steps):
+    """After the playlist key changed, every row on a node has the revision the
+    local copy has. All of it is sealed again under the current key, no
+    revision goes down, and a body nothing here can name is dropped."""
+    s = steps["a node sealed under the previous key"]
+    assert s["readable"] == s["kinds"], "a row is still sealed under the old key"
+    assert s["remaining"] == s["kinds"], "the unknown body was not dropped"
+    assert s["revsNotLowered"] is True
+
+
 def test_what_a_playlist_costs_sealed_is_measured_not_quoted(steps):
     """The ceiling the UI promises comes from here, not from the design doc.