feat(node): Music app node-side — indexing, MusicBrainz enrichment, protocol

Implements the node half of docs/musicbay.md against MNP 0.8:

- IndexEntry gains artist/album/track_no (reuses duration/thumb_hash/
  display_title, already generic). New musicbrainz_config/_enabled and
  music_meta_req/_resp message pairs, mirroring the TMDB shape.
- title_parse.parse_track_filename: track-number-prefix + title parsing,
  fallback-only (embedded tags are the primary source, unlike Videos).
- indexer.enrich_audio.AudioEnricher: mutagen-based tag/embedded-cover
  extraction through its own bounded pool (asyncio.to_thread, no
  subprocess — no ffmpeg-shaped deadlock risk). Gated on "music" in a
  group's enabled_apps rather than a video_root-style scoped folder.
- musicbrainz.py: MusicBrainzClient — no API key (unlike TMDB), just a
  self-imposed ~1 req/s pace and a configurable, non-default User-Agent
  contact string; inert (no calls at all) when no contact is configured,
  never sends an unidentified client.
- media_cache.py: file_mbid/mbid_meta tables alongside the existing TMDB
  ones, cover art reusing the thumbs table via a synthetic
  musicbrainz:{mbid} id, pruned on file deletion.
- roster.py/ops.py/webrtc_server.py: musicbrainz_contact (node-wide) and
  musicbrainz_enabled (per-group, from the start) as signed operator
  settings, ALLOWED_APPS gains "music", _do_music_meta_request resolves
  and caches a release-level MusicBrainz match per (artist, album).
- daemon.py: AudioEnricher/MusicBrainzClient wired alongside the video
  ones; a group's existing library is swept when "music" is newly
  enabled (no video_root equivalent — see musicbay.md §2.1).

41 new tests (musicbrainz.py against a mocked transport, admin-op policy
for both new settings, media_cache round-trip/pruning, enrich_audio
end-to-end against real ffmpeg-generated MP3s). Full suite (common +
node + hub): 1116 passed, no regressions.

Client-side (music-app.js, persistent player bar) not started yet.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KBi7ALLGfwcjBXt57yNMcy

1 files changed, 33 insertions, 0 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/roster.py b/packages/meshbay-node/src/meshbay_node/roster.py
index b4efb7c..24424ab 100644
--- a/packages/meshbay-node/src/meshbay_node/roster.py
+++ b/packages/meshbay-node/src/meshbay_node/roster.py
@@ -665,6 +665,39 @@ class Roster:
         await self.set_setting(group_id, self.SETTING_TMDB_ENABLED,
                                "1" if enabled else "0", set_by)
 
+    # The Music app's MusicBrainz contact string (docs/musicbay.md §3.2) —
+    # node-wide, under the same group_id="" sentinel as the TMDB token/
+    # language above, for the identical reason: one operator's User-Agent
+    # identity, not a per-group concern. Unlike TMDB there is no secret to
+    # store — this is the contact MusicBrainz's usage policy asks a client
+    # to identify itself with, not a credential. Unset means "no contact
+    # configured", which musicbrainz.py treats as "make no calls at all"
+    # (docs/musicbay.md §3.1) rather than sending an unidentified client.
+    SETTING_MUSICBRAINZ_CONTACT = "musicbrainz_contact"
+
+    async def musicbrainz_contact(self) -> str | None:
+        return await self.get_setting(
+            self.NODE_WIDE_GROUP_ID, self.SETTING_MUSICBRAINZ_CONTACT) or None
+
+    async def set_musicbrainz_contact(self, contact: str | None = None, set_by: str = "") -> None:
+        """`contact=""` clears it; `contact=None` leaves it unchanged (tmdb_config's shape)."""
+        if contact is not None:
+            await self.set_setting(self.NODE_WIDE_GROUP_ID, self.SETTING_MUSICBRAINZ_CONTACT,
+                                   contact, set_by)
+
+    # Whether MusicBrainz lookups run for this group at all — per-group from
+    # the start (unlike tmdb_enabled, which started node-wide and moved
+    # per-group later once the lesson was already learned). Unset means on,
+    # same "absent means the old behaviour" discipline as everything else.
+    SETTING_MUSICBRAINZ_ENABLED = "musicbrainz_enabled"
+
+    async def musicbrainz_enabled(self, group_id: str) -> bool:
+        return (await self.get_setting(group_id, self.SETTING_MUSICBRAINZ_ENABLED, "1")) != "0"
+
+    async def set_musicbrainz_enabled(self, group_id: str, enabled: bool, set_by: str = "") -> None:
+        await self.set_setting(group_id, self.SETTING_MUSICBRAINZ_ENABLED,
+                               "1" if enabled else "0", set_by)
+
     # How often the indexer's reconciliation backstop runs, and how long it
     # waits after the last change on a file before hashing it. Unset means
     # the indexer's own defaults — an existing group's behaviour must not