Use "real" params for format as well

lib/SugarTrail.pm

     &helper::dmup (real_params => $params);
 
     my ($stpath, $query) = splat;
-    my $format = params->{__format} // 'plain';
+    my $format = $params->{__format} // 'plain';
     header('Content-Type' => ( 
             $format eq 'html' ? 'text/html' : 'text/plain'
     ));