feat(library): match own-state on artist MBID, not just name

Own-state ("in library") relied on an exact artist-NAME match, so an owned
album whose name differed from the MB canonical (punctuation/locale/feat.)
showed as not-owned even when followed. Capture the MusicBrainz artist MBID
on LibraryItem and prefer it for matching.

- New LibraryItem.artistMbid (migration add_library_artist_mbid). Populated at
  import (pipeline) + scan, both of which already hold the resolved target;
  the pipeline also now stores rgMbid (it previously didn't). COALESCE on
  conflict backfills MBIDs on re-scan without clobbering.
- /api/artists "in library, not followed" matches by artistMbid first, name
  case-insensitively as fallback (rows predating the column). Library route
  prefers the item's own artistMbid over the release join.

Last.fm/discover own-state still use name-match (they work) — a smaller
follow-up. worker 233, web 186 tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/prisma/migrations/20260714195144_add_library_artist_mbid/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "LibraryItem" ADD COLUMN     "artistMbid" TEXT;

web/prisma/schema.prisma

@@ -89,6 +89,10 @@ model LibraryItem {
   // MusicBrainz release-group MBID when known (resolved at manual import) — gives the album
   // cover art without depending on a matching MonitoredRelease row.
   rgMbid       String?
+  // MusicBrainz ARTIST MBID when known (captured at import + scan). Own-state ("in library")
+  // prefers this over the fragile exact artist-name match; null rows fall back to name-match
+  // (re-scan to populate).
+  artistMbid   String?
   // The album's on-disk audio filenames ("## Title.ext"), captured at import + scan, so the
   // Library modal can show the REAL tracks on disk (revealing incomplete/edition mismatches)
   // instead of MusicBrainz's canonical listing. Empty for items imported before this existed

web/src/app/api/artists/route.test.ts

@@ -98,6 +98,16 @@ describe("artists collection API", () => {
     expect(body.ownedNotFollowed).not.toContain("followed artist"); // case-insensitive match
   });
 
+  it("GET matches owned artists to the watched roster by MBID despite a name mismatch", async () => {
+    // followed under the canonical MB name, but the library row's name differs (feat./locale)
+    await prisma.watchedArtist.create({ data: { mbid: "mb-beyonce", name: "Beyoncé" } });
+    await prisma.libraryItem.create({
+      data: { artist: "Beyonce", album: "Lemonade", artistMbid: "mb-beyonce", path: "/l", source: "scan", format: "FLAC", qualityClass: 2 },
+    });
+    const body = await (await GET(listReq())).json();
+    expect(body.ownedNotFollowed).not.toContain("Beyonce"); // matched by MBID → not "unfollowed"
+  });
+
   it("GET ?mbid= returns the follow state for a single artist", async () => {
     await prisma.watchedArtist.create({ data: { mbid: "followed-1", name: "Followed" } });
     expect((await (await GET(listReq("?mbid=followed-1"))).json()).followed).toBe(true);

web/src/app/api/artists/route.ts

@@ -20,16 +20,21 @@ export async function GET(request: Request) {
         },
       },
     }),
-    prisma.libraryItem.findMany({ select: { artist: true }, distinct: ["artist"] }),
+    prisma.libraryItem.findMany({ select: { artist: true, artistMbid: true } }),
   ]);
 
-  // Artists you own music by (LibraryItem) but don't follow yet — name-matched
-  // case-insensitively against the watched roster (the have-via-scan name-match caveat).
+  // Artists you own music by (LibraryItem) but don't follow yet. Match on the MusicBrainz
+  // ARTIST MBID first (robust to name punctuation/locale/feat. variants), falling back to a
+  // case-insensitive name match for library rows that predate the artistMbid column.
+  const followedMbids = new Set(artists.map((a) => a.mbid));
   const followedNames = new Set(artists.map((a) => a.name.trim().toLowerCase()));
-  const ownedNotFollowed = libraryArtists
-    .map((r) => r.artist)
-    .filter((name) => name.trim() && !followedNames.has(name.trim().toLowerCase()))
-    .sort((a, b) => a.localeCompare(b));
+  const isFollowed = (r: { artist: string; artistMbid: string | null }) =>
+    (r.artistMbid && followedMbids.has(r.artistMbid)) || followedNames.has(r.artist.trim().toLowerCase());
+  const ownedNotFollowed = [
+    ...new Set(
+      libraryArtists.filter((r) => r.artist.trim() && !isFollowed(r)).map((r) => r.artist),
+    ),
+  ].sort((a, b) => a.localeCompare(b));
 
   return Response.json({
     artists: artists.map((a) => {