fix(jellyfin): resolve genre id as a MusicGenre item

The Jellyfin /Items/{id} endpoint resolved albums, artists, songs and
playlists by id but not genres, so a genre id returned 404. Finamp's
genre "See all" fetches the genre as the track list's parent item, and
that 404 crashed its screen to a blank page after the tracks flashed in.

Add a Genre lookup to resolveItemByID (backed by a new GenreRepository.Get)
so a genre id returns its MusicGenre BaseItemDto, matching real Jellyfin.

model/genre.go

@@ -11,4 +11,5 @@ type Genres []Genre
 
 type GenreRepository interface {
 	GetAll(...QueryOptions) (Genres, error)
+	Get(id string) (*Genre, error)
 }

persistence/genre_repository.go

@@ -30,15 +30,19 @@ func (r *genreRepository) GetAll(opt ...model.QueryOptions) (model.Genres, error
 	return res, err
 }
 
-// Override ResourceRepository methods to return Genre objects instead of Tag objects
-
-func (r *genreRepository) Read(id string) (any, error) {
+func (r *genreRepository) Get(id string) (*model.Genre, error) {
 	sel := r.selectGenre().Where(Eq{"tag.id": id})
 	var res model.Genre
 	err := r.queryOne(sel, &res)
 	return &res, err
 }
 
+// Override ResourceRepository methods to return Genre objects instead of Tag objects
+
+func (r *genreRepository) Read(id string) (any, error) {
+	return r.Get(id)
+}
+
 func (r *genreRepository) ReadAll(options ...rest.QueryOptions) (any, error) {
 	return r.GetAll(r.parseRestOptions(r.ctx, options...))
 }

server/jellyfin/items.go

@@ -736,7 +736,7 @@ func (api *Router) listPlaylists(ctx context.Context, opts model.QueryOptions, q
 }
 
 // resolveItemByID resolves a decoded navidrome id to its BaseItemDto, trying library view, album,
-// artist, song and playlist in turn. Albums and songs report not-found when the user lacks access
+// artist, song, playlist and genre in turn. Albums and songs report not-found when the user lacks access
 // to their library, so an id can't probe content outside the user's libraries.
 func (api *Router) resolveItemByID(ctx context.Context, id string, fields dto.Fields) (dto.BaseItemDto, bool) {
 	// The synthetic playlists folder must resolve by the id we advertised, not 404.
@@ -778,6 +778,9 @@ func (api *Router) resolveItemByID(ctx context.Context, id string, fields dto.Fi
 	if pl, err := api.playlists.Get(ctx, id); err == nil {
 		return dto.PlaylistToBaseItem(*pl, fields), true
 	}
+	if g, err := api.ds.Genre(ctx).Get(id); err == nil {
+		return dto.GenreToBaseItem(*g), true
+	}
 	return dto.BaseItemDto{}, false
 }
 

server/jellyfin/items_test.go

@@ -917,6 +917,21 @@ var _ = Describe("Items", func() {
 			Expect(w.Code).To(Equal(http.StatusNotFound))
 		})
 
+		// Finamp's genre "See all" fetches the genre by id; a 404 white-screens it (see resolveItemByID).
+		It("resolves a genre id as a MusicGenre item", func() {
+			Expect(ds.Genre(context.Background()).(*tests.MockedGenreRepo).Put(&model.Genre{ID: "g1", Name: "Rock"})).To(Succeed())
+			w := httptest.NewRecorder()
+			r := httptest.NewRequest("GET", "/Items/"+dto.EncodeID("g1"), nil).WithContext(ctxUser())
+			r = withChiURLParam(r, "itemId", dto.EncodeID("g1"))
+			invoke(api.getItem, w, r)
+			Expect(w.Code).To(Equal(http.StatusOK))
+			var item dto.BaseItemDto
+			Expect(json.Unmarshal(w.Body.Bytes(), &item)).To(Succeed())
+			Expect(item.Id).To(Equal(dto.EncodeID("g1")))
+			Expect(item.Name).To(Equal("Rock"))
+			Expect(item.Type).To(Equal("MusicGenre"))
+		})
+
 		It("resolves a library-view id for an admin even though their Libraries slice is empty", func() {
 			ds.Library(context.Background()).(*tests.MockLibraryRepo).SetData(model.Libraries{{ID: 1, Name: "Music Library"}})
 			w := httptest.NewRecorder()

tests/mock_genre_repo.go

@@ -32,6 +32,17 @@ func (r *MockedGenreRepo) GetAll(options ...model.QueryOptions) (model.Genres, e
 	return all, nil
 }
 
+func (r *MockedGenreRepo) Get(id string) (*model.Genre, error) {
+	if r.Error != nil {
+		return nil, r.Error
+	}
+	r.init()
+	if g, ok := r.Data[id]; ok {
+		return &g, nil
+	}
+	return nil, model.ErrNotFound
+}
+
 func (r *MockedGenreRepo) Put(g *model.Genre) error {
 	if r.Error != nil {
 		return r.Error