fix: address fourth code review findings

- Fix FK constraint violation in SyncArtistDiscography: delete
  notifications_sent rows before external_releases to prevent
  constraint failure when re-syncing artists with prior notifications.
- Implement per-artist type filtering: FilterReleaseGroups now accepts
  FilterOptions with IgnoreSingles/IgnoreCompilations flags, read from
  artist_settings table via getArtistFilterOptions.
- Fix inconsistent error wrapping: GetExternalRelease now wraps errors
  with fmt.Errorf like all other functions in the package; updated test
  to use errors.Is for sql.ErrNoRows check.
- Add tests: FilterReleaseGroups ignore singles/compilations,
  SyncArtistDiscography per-artist type filtering, and FK-safe resync.

internal/musicbrainz/sync_test.go

@@ -740,3 +740,152 @@ func TestSyncArtistDiscography_CleansStaleReleases(t *testing.T) {
 		}
 	}
 }
+
+// -----------------------------------------------------------------------
+// Test: per-artist ignore_singles filters out Single type
+// -----------------------------------------------------------------------
+func TestSyncArtistDiscography_IgnoreSingles(t *testing.T) {
+	artistMBID := "artist-singles-test"
+	artistName := "Singles Artist"
+
+	server := newTestMBServer(func(w http.ResponseWriter, r *http.Request) {
+		resp := mbReleaseGroupListResponse(
+			mbReleaseGroupXML("rg-1", "Album", "Album", "Official", artistMBID, artistName, "2024-01-01")+
+				mbReleaseGroupXML("rg-2", "Single", "Single", "Official", artistMBID, artistName, "2024-02-01"),
+			2,
+		)
+		w.Write([]byte(resp))
+	})
+	defer server.Close()
+
+	db := newTestDB(t)
+	defer db.Close()
+	// Seed artist with ignore_singles = true.
+	if _, err := db.Conn().Exec(
+		"INSERT INTO artist_settings (id, name, ignore_singles, monitored) VALUES (?, ?, 1, 1)",
+		artistMBID, artistName,
+	); err != nil {
+		t.Fatalf("seed artist: %v", err)
+	}
+
+	client := newTestClient(server.URL)
+	ctx := context.Background()
+
+	releases, err := SyncArtistDiscography(ctx, client, db, artistMBID, 0)
+	if err != nil {
+		t.Fatalf("SyncArtistDiscography() error: %v", err)
+	}
+	if len(releases) != 1 {
+		t.Fatalf("expected 1 release (singles filtered), got %d", len(releases))
+	}
+	if releases[0].Type != "Album" {
+		t.Errorf("expected type Album, got %s", releases[0].Type)
+	}
+}
+
+// -----------------------------------------------------------------------
+// Test: per-artist ignore_compilations filters out Compilation type
+// -----------------------------------------------------------------------
+func TestSyncArtistDiscography_IgnoreCompilations(t *testing.T) {
+	artistMBID := "artist-comp-test"
+	artistName := "Comp Artist"
+
+	server := newTestMBServer(func(w http.ResponseWriter, r *http.Request) {
+		resp := mbReleaseGroupListResponse(
+			mbReleaseGroupXML("rg-1", "Album", "Album", "Official", artistMBID, artistName, "2024-01-01")+
+				mbReleaseGroupXML("rg-2", "Best Of", "Compilation", "Official", artistMBID, artistName, "2024-02-01"),
+			2,
+		)
+		w.Write([]byte(resp))
+	})
+	defer server.Close()
+
+	db := newTestDB(t)
+	defer db.Close()
+	// Seed artist with ignore_compilations = true.
+	if _, err := db.Conn().Exec(
+		"INSERT INTO artist_settings (id, name, ignore_compilations, monitored) VALUES (?, ?, 1, 1)",
+		artistMBID, artistName,
+	); err != nil {
+		t.Fatalf("seed artist: %v", err)
+	}
+
+	client := newTestClient(server.URL)
+	ctx := context.Background()
+
+	releases, err := SyncArtistDiscography(ctx, client, db, artistMBID, 0)
+	if err != nil {
+		t.Fatalf("SyncArtistDiscography() error: %v", err)
+	}
+	if len(releases) != 1 {
+		t.Fatalf("expected 1 release (compilations filtered), got %d", len(releases))
+	}
+	if releases[0].Type != "Album" {
+		t.Errorf("expected type Album, got %s", releases[0].Type)
+	}
+}
+
+// -----------------------------------------------------------------------
+// Test: resync with notifications_sent does not violate FK constraint
+// -----------------------------------------------------------------------
+func TestSyncArtistDiscography_ResyncWithNotifications(t *testing.T) {
+	artistMBID := "artist-fk-test"
+	artistName := "FK Artist"
+
+	server := newTestMBServer(func(w http.ResponseWriter, r *http.Request) {
+		resp := mbReleaseGroupListResponse(
+			mbReleaseGroupXML("rg-1", "Album", "Album", "Official", artistMBID, artistName, "2024-01-01"),
+			1,
+		)
+		w.Write([]byte(resp))
+	})
+	defer server.Close()
+
+	db := newTestDB(t)
+	defer db.Close()
+	seedArtist(t, db, artistMBID, artistName)
+
+	client := newTestClient(server.URL)
+	ctx := context.Background()
+
+	// First sync.
+	_, err := SyncArtistDiscography(ctx, client, db, artistMBID, 24*time.Hour)
+	if err != nil {
+		t.Fatalf("first SyncArtistDiscography() error: %v", err)
+	}
+
+	// Insert a notifications_sent row referencing the release.
+	_, err = db.Conn().Exec(
+		"INSERT INTO notifications_sent (rgid) VALUES (?)", "rg-1",
+	)
+	if err != nil {
+		t.Fatalf("insert notification: %v", err)
+	}
+
+	// Force cache expiry.
+	_, err = db.Conn().Exec("UPDATE external_releases SET cached_at = ? WHERE artist_id = ?",
+		time.Now().Add(-48*time.Hour).Format("2006-01-02 15:04:05"), artistMBID)
+	if err != nil {
+		t.Fatalf("expire cache: %v", err)
+	}
+
+	// Second sync should succeed without FK violation.
+	releases, err := SyncArtistDiscography(ctx, client, db, artistMBID, 24*time.Hour)
+	if err != nil {
+		t.Fatalf("second SyncArtistDiscography() error (FK violation?): %v", err)
+	}
+	if len(releases) != 1 {
+		t.Fatalf("expected 1 release after resync, got %d", len(releases))
+	}
+
+	// Notification should have been cleaned up.
+	var count int
+	err = db.Conn().QueryRow("SELECT COUNT(*) FROM notifications_sent WHERE rgid = ?", "rg-1").Scan(&count)
+	if err != nil {
+		t.Fatalf("count notifications: %v", err)
+	}
+	if count != 0 {
+		t.Errorf("expected 0 notifications after resync, got %d", count)
+	}
+}
+