refactor(mnp)!: one operation for an app's folders, not one per app

`video_root`, `audio_root` and `photo_roots` are gone — the messages, the
signed operations, the handlers, the `ops` wrappers, the three scalars on the
handshake ack, and the client's handlers for their acks. `app_directories`
does the same thing for every application, keyed by the app's own registry
name, and it is what the SPA has been sending.

The three were the same instruction three times, differing only in the key they
wrote and whether they carried a string or a list. That shape is what made
adding an application mean adding a message type, an op, a handler and a widget;
it also meant three validation paths, and the older ones validated nothing —
a typo was stored and then quietly matched no entry, an app showing an empty tab
with no way to tell "misconfigured" from "no files yet".

**What stays, and why.** `Roster.LEGACY_DIR_KEYS` still reads `video_root` and
friends out of `group_settings`: that is a key on an operator's disk, not on the
wire, and a node upgraded into this must find its own configuration. The Search
page still reads its own older cache keys, for the same reason — the cache
outlives a deploy. `CTX_ALIASES` keeps only `chat`, which is the one app whose
second name something still reads.

The two per-app policy test files go with the messages. What only they held —
the real challenge/response path from message to database, which no other test
exercises — is retargeted at `app_directories` in
`test_app_directories_signed.py`, and the handler's own refusals (unknown app,
malformed `directories`, nobody to authorize it) join `test_app_directories.py`.

Node and common suites 1368 passed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AsoWC3GmhNdwVFomW3QjH3

1 files changed, 8 insertions, 6 deletions

diff --git a/packages/meshbay-hub/tests/test_app_settings_plugin.py b/packages/meshbay-hub/tests/test_app_settings_plugin.py
index 892fd09..af86f12 100644
--- a/packages/meshbay-hub/tests/test_app_settings_plugin.py
+++ b/packages/meshbay-hub/tests/test_app_settings_plugin.py
@@ -254,17 +254,19 @@ def test_each_app_takes_a_list_of_directories(app, prop):
             f"{app} still reads {singular} — one shape per idea")
 
 
-def test_an_older_node_still_fills_the_lists():
+def test_the_lists_are_read_under_one_name_each():
     """
-    A node speaking MNP 1.0 sends `video_root`, not `video_directories`.
-    Reading the missing plural as "nothing configured" would empty a working
-    Videos tab on every group hosted by a node that has not been upgraded.
+    One name per app on the ack — `<app>_directories`, always a list. A second
+    name for the same answer means a page that reads whichever it thinks of
+    first, and a node that fills only the other one empties a working tab.
     """
     page = GROUP_PAGE.read_text(encoding="utf-8")
     block = page[page.index("setAppDirectories({"):]
     block = block[:block.index("setChatDirectory")]
-    assert "ack.video_root" in block and "ack.audio_root" in block
-    assert "ack.photo_roots" in block
+    assert "ack.video_directories" in block and "ack.music_directories" in block
+    assert "ack.photo_directories" in block
+    for gone in ("ack.video_root", "ack.audio_root", "ack.photo_roots"):
+        assert gone not in block, f"{gone} is a second name for the same answer"
 
 
 def test_the_search_cache_reads_both_shapes():