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, 5 insertions, 7 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/roster.py b/packages/meshbay-node/src/meshbay_node/roster.py
index ae0b4cf..b7fbf8e 100644
--- a/packages/meshbay-node/src/meshbay_node/roster.py
+++ b/packages/meshbay-node/src/meshbay_node/roster.py
@@ -817,14 +817,12 @@ class Roster:
         "photo": ("photo_roots", "list"),
     }
 
-    # The name each app's directories are *also* published under, for readers
-    # that predate the list — the handshake ack's `video_root`, and the group
-    # context the ack builds from. Derived from the list, never stored beside
-    # it, so the two cannot disagree; the shape says how to derive it.
+    # The name an app's directories are *also* published under, where
+    # something reads that name. Chat is the only one: it has a single
+    # destination, the handshake ack publishes it as `chat_directory`, and the
+    # paperclip reads it. Derived from the list, never stored beside it, so the
+    # two cannot disagree; the shape says how to derive it.
     CTX_ALIASES = {
-        "video": ("video_root", "scalar"),
-        "music": ("audio_root", "scalar"),
-        "photo": ("photo_roots", "list"),
         "chat": ("chat_directory", "scalar"),
     }