fix(server/m7-379): enricher leaves cover_art_source NULL when MBID missing

internal/coverart/enricher.go

@@ -63,11 +63,15 @@ func (e *Enricher) EnrichAlbum(ctx context.Context, albumID pgtype.UUID) error {
 	}
 
 	// Step 2: MBCAA fallback. Requires fetcher + toggle on + MBID.
+	// When the toggle is disabled OR the album has no MBID, leave
+	// cover_art_source NULL so a future scan can retry once the
+	// scanner heals the MBID. 'none' is reserved for genuine MBCAA
+	// 404s where we know the album really isn't in the archive.
 	if !e.mbcaaOn || e.fetcher == nil {
-		return e.recordCover(ctx, albumID, "", "none")
+		return nil
 	}
 	if row.Mbid == nil || *row.Mbid == "" {
-		return e.recordCover(ctx, albumID, "", "none")
+		return nil
 	}
 
 	body, err := e.fetcher.Fetch(ctx, *row.Mbid)

internal/coverart/enricher_test.go

@@ -101,7 +101,7 @@ func TestEnrichAlbum_SidecarFound(t *testing.T) {
 	}
 }
 
-func TestEnrichAlbum_NoSidecarNoMBID_RecordsNone(t *testing.T) {
+func TestEnrichAlbum_NoSidecarNoMBID_LeavesNull(t *testing.T) {
 	pool := newPool(t)
 	id, _ := seedAlbumWithTrack(t, pool, "NoMbid", "Artist", "")
 	e := NewEnricher(pool, discardLogger(), nil, true)
@@ -112,8 +112,8 @@ func TestEnrichAlbum_NoSidecarNoMBID_RecordsNone(t *testing.T) {
 	if err != nil {
 		t.Fatalf("get: %v", err)
 	}
-	if row.CoverArtSource == nil || *row.CoverArtSource != "none" {
+	if row.CoverArtSource != nil {
-		t.Errorf("source = %v, want 'none'", row.CoverArtSource)
+		t.Errorf("source = %v, want nil (NULL — eligible for retry on next scan)", row.CoverArtSource)
 	}
 }