fix: address code review findings

internal/musicbrainz/api.go

@@ -120,13 +120,16 @@ func IsTypeIncluded(releaseType string) bool {
 // MBID) must NOT be stored here, because artist_settings is keyed by the
 // Navidrome ID and the foreign key / join would otherwise never match.
 func (rg *ReleaseGroup) ToExternalRelease(artistID string) *database.ExternalRelease {
-	// Only the primary type is persisted; secondary types are used transiently
-	// for filtering above and are not stored in the external_releases schema.
+	// The primary type and the secondary types are both persisted so that the
+	// cache-hit path in SyncArtistDiscography can re-apply the same
+	// IgnoreSingles / IgnoreCompilations rules (which consider secondary types)
+	// as the cache-miss path, keeping results stable across cache refreshes.
 	return &database.ExternalRelease{
-		RGID:        rg.ID,
-		ArtistID:    artistID,
-		Title:       rg.Title,
-		Type:        rg.Type,
-		ReleaseDate: rg.ReleaseDate,
+		RGID:           rg.ID,
+		ArtistID:       artistID,
+		Title:          rg.Title,
+		Type:           rg.Type,
+		ReleaseDate:    rg.ReleaseDate,
+		SecondaryTypes: rg.SecondaryTypes,
 	}
 }