fix(jellyfin): separate "Featured On" from an artist's own discography

Jellify's artist page fetches the discography via albumArtistIds and the
"Featured On" section via contributingArtistIds, relying on the server to
return disjoint sets. We collapsed albumArtistIds/artistIds/
contributingArtistIds into one AlbumsByArtistID filter, so an artist's own
albums appeared in both sections.

Add AlbumsByContributingArtistID — albums where the artist is a track
artist but NOT the album artist — matching Jellyfin's ContributingArtistIds
(in Artists, not in AlbumArtists), and route contributingArtistIds to it.

server/filter/filters.go

@@ -61,6 +61,20 @@ func AlbumsByArtistID(artistId string) Options {
 	})
 }
 
+// AlbumsByContributingArtistID matches albums where the artist appears as a track (performing)
+// artist but is NOT the album artist — Jellyfin's ContributingArtistIds / the "Featured On"
+// section. It is the disjoint complement of AlbumsByArtistID's album-artist match, so an artist's
+// own discography never leaks into their "appears on" list.
+func AlbumsByContributingArtistID(artistId string) Options {
+	return addDefaultFilters(Options{
+		Sort: "max_year",
+		Filters: And{
+			persistence.Exists("json_tree(participants, '$.artist')", Eq{"value": artistId}),
+			persistence.NotExists("json_tree(participants, '$.albumartist')", Eq{"value": artistId}),
+		},
+	})
+}
+
 func AlbumsByYear(fromYear, toYear int) Options {
 	orderOption := ""
 	if fromYear > toYear {

server/jellyfin/e2e/browsing_test.go

@@ -117,6 +117,19 @@ var _ = Describe("Browsing", func() {
 			q := queryResult(get("/Items?IncludeItemTypes=Audio&Recursive=true&ArtistIds=" + enc(artistID("Miles Davis"))))
 			Expect(names(q.Items)).To(ConsistOf("So What"))
 		})
+
+		// contributingArtistIds is Jellify's "Featured On" section: albums the artist only appears
+		// on, which must exclude their own discography (albums where they are the album artist).
+		It("lists Featured On albums (contributingArtistIds) a performer only guests on", func() {
+			q := queryResult(get("/Items?IncludeItemTypes=MusicAlbum&Recursive=true&contributingArtistIds=" + enc(artistID("Featured Guest"))))
+			Expect(names(q.Items)).To(ConsistOf("Singles"))
+		})
+
+		It("excludes an album artist's own discography from Featured On (contributingArtistIds)", func() {
+			q := queryResult(get("/Items?IncludeItemTypes=MusicAlbum&Recursive=true&contributingArtistIds=" + enc(artistID("The Beatles"))))
+			Expect(names(q.Items)).ToNot(ContainElement("Abbey Road"))
+			Expect(names(q.Items)).ToNot(ContainElement("Help!"))
+		})
 	})
 
 	// Jellify (and the official Jellyfin TypeScript SDK) send query params in camelCase

server/jellyfin/items.go

@@ -65,11 +65,14 @@ func (api *Router) queryItems(ctx context.Context, r *http.Request) (dto.QueryRe
 	// An artist's page filters by artist, not by ParentId: Finamp sends ParentId=<libraryId> for
 	// scoping plus AlbumArtistIds/ArtistIds/contributingArtistIds for the artist itself. Without
 	// this, an artist's albums/tracks come back unfiltered (all artists).
-	artistId := firstDecodedID(firstNonEmpty(
-		p.StringOr("albumartistids", ""),
-		p.StringOr("artistids", ""),
-		p.StringOr("contributingartistids", ""),
-	))
+	//
+	// albumArtistIds/artistIds select the artist's own discography; contributingArtistIds alone
+	// selects albums the artist merely appears on (Jellyfin's "Featured On"), which must exclude
+	// that discography — otherwise their own albums show up in both sections.
+	albumArtistScope := firstNonEmpty(p.StringOr("albumartistids", ""), p.StringOr("artistids", ""))
+	contributingScope := p.StringOr("contributingartistids", "")
+	artistId := firstDecodedID(firstNonEmpty(albumArtistScope, contributingScope))
+	contributingOnly := albumArtistScope == "" && contributingScope != ""
 
 	scopeIDs, isLibraryParent := resolveLibraryScope(ctx, parentId)
 	// When no item type is requested and ParentId is an album, browse into that album's tracks:
@@ -92,7 +95,7 @@ func (api *Router) queryItems(ctx context.Context, r *http.Request) (dto.QueryRe
 	if len(types) == 1 {
 		opts := model.QueryOptions{Offset: offset, Max: limit}
 		applySort(&opts, types[0], sortBy, sortOrder)
-		return api.queryItemsOfType(ctx, types[0], opts, entityParent, artistId, scopeIDs, search, favOnly)
+		return api.queryItemsOfType(ctx, types[0], opts, entityParent, artistId, contributingOnly, scopeIDs, search, favOnly)
 	}
 
 	var items []dto.BaseItemDto
@@ -100,7 +103,7 @@ func (api *Router) queryItems(ctx context.Context, r *http.Request) (dto.QueryRe
 	for _, itemType := range types {
 		var opts model.QueryOptions
 		applySort(&opts, itemType, sortBy, sortOrder)
-		res, err := api.queryItemsOfType(ctx, itemType, opts, entityParent, artistId, scopeIDs, search, favOnly)
+		res, err := api.queryItemsOfType(ctx, itemType, opts, entityParent, artistId, contributingOnly, scopeIDs, search, favOnly)
 		if err != nil {
 			return dto.QueryResult{}, err
 		}
@@ -110,7 +113,7 @@ func (api *Router) queryItems(ctx context.Context, r *http.Request) (dto.QueryRe
 	return result(paginate(items, offset, limit), total, offset), nil
 }
 
-func (api *Router) queryItemsOfType(ctx context.Context, itemType string, opts model.QueryOptions, entityParent, artistId string, scopeIDs []int, search string, favOnly bool) (dto.QueryResult, error) {
+func (api *Router) queryItemsOfType(ctx context.Context, itemType string, opts model.QueryOptions, entityParent, artistId string, contributingOnly bool, scopeIDs []int, search string, favOnly bool) (dto.QueryResult, error) {
 	switch itemType {
 	case "Audio":
 		return api.listSongs(ctx, opts, entityParent, artistId, scopeIDs, search, favOnly)
@@ -122,7 +125,7 @@ func (api *Router) queryItemsOfType(ctx context.Context, itemType string, opts m
 	case "Playlist":
 		return api.listPlaylists(ctx, opts, favOnly)
 	default: // MusicAlbum
-		return api.listAlbums(ctx, opts, entityParent, artistId, scopeIDs, search, favOnly)
+		return api.listAlbums(ctx, opts, entityParent, artistId, contributingOnly, scopeIDs, search, favOnly)
 	}
 }
 
@@ -180,14 +183,18 @@ func paginate(items []dto.BaseItemDto, offset, limit int) []dto.BaseItemDto {
 	return items
 }
 
-func (api *Router) listAlbums(ctx context.Context, opts model.QueryOptions, parentId, artistId string, scopeIDs []int, search string, fav bool) (dto.QueryResult, error) {
+func (api *Router) listAlbums(ctx context.Context, opts model.QueryOptions, parentId, artistId string, contributingOnly bool, scopeIDs []int, search string, fav bool) (dto.QueryResult, error) {
 	repo := api.ds.Album(ctx)
 	filters := squirrel.And{}
 	// For albums, both ParentId (browse into an artist) and AlbumArtistIds/ArtistIds mean "this
-	// artist's albums".
-	if scope := firstNonEmpty(artistId, parentId); scope != "" {
-		filters = append(filters, filter.AlbumsByArtistID(scope).Filters)
-	} else {
+	// artist's albums"; contributingArtistIds instead means "albums this artist only appears on"
+	// (Featured On), which excludes their own discography.
+	switch {
+	case contributingOnly && artistId != "":
+		filters = append(filters, filter.AlbumsByContributingArtistID(artistId).Filters)
+	case firstNonEmpty(artistId, parentId) != "":
+		filters = append(filters, filter.AlbumsByArtistID(firstNonEmpty(artistId, parentId)).Filters)
+	default:
 		filters = append(filters, notMissing)
 	}
 	if fav {