harden deezer auth errors and mixed playlist preflight

internal/app/app.go

@@ -728,6 +728,20 @@ func (m *Main) ripPlaylist(ctx context.Context, p provider.Client, source, playl
 }
 
 func (m *Main) ripPlaylistMixed(ctx context.Context, playlistID, name string, refs []PlaylistTrackRef) error {
+	requiredSources := map[string]struct{}{}
+	for _, ref := range refs {
+		s := strings.TrimSpace(ref.Source)
+		if s == "" {
+			continue
+		}
+		requiredSources[s] = struct{}{}
+	}
+	for source := range requiredSources {
+		if err := m.requireSourceDownloadAuth(source); err != nil {
+			return err
+		}
+	}
+
 	folder := filepath.Join(m.Config.Session.Downloads.Folder, naming.CleanName(name, naming.Config{
 		RestrictCharacters: m.Config.Session.Filepaths.RestrictCharacters,
 		TruncateTo:         m.Config.Session.Filepaths.TruncateTo,

internal/app/app_test.go

@@ -535,6 +535,16 @@ func TestRipAlbumRequiresDeezerARL(t *testing.T) {
 	}
 }
 
+func TestRipPlaylistMixedRequiresDeezerAuth(t *testing.T) {
+	d := config.DefaultConfigData()
+	m := &Main{Config: &config.Config{File: d, Session: d}}
+
+	err := m.ripPlaylistMixed(context.Background(), "mix1", "Mix", []PlaylistTrackRef{{Source: "deezer", ID: "1"}})
+	if err == nil || !strings.Contains(err.Error(), "deezer") {
+		t.Fatalf("expected deezer auth error, got %v", err)
+	}
+}
+
 func TestApplyQobuzArtistFiltersRepeats(t *testing.T) {
 	albums := []collectionAlbum{
 		{ID: "a1", Title: "Album X", BitDepth: 16, Sampling: 44.1, Explicit: false},