Problem adding a tab to the user menu

I created a panel page using the Panels module, Contact list at the path messages/contact-list.

The Privatemsg module causes several tabs (Inbox, Sent messages, All messages) to be displayed across the top of pages with path messages. I am attempting to add an additional tab that links to my Panels page, Contact list.

Based on the code in privatemsg.module for the "Sent messages" tab:

  $items['messages/sent'] = array(
    'title'            => 'Sent messages',
    'page callback'    => 'privatemsg_list_page',
    'page arguments'   => array('sent'),
    'file'             => 'privatemsg.pages.inc',
    'file path'        => drupal_get_path('module', 'privatemsg'),
    'access callback'  => 'privatemsg_user_access',
    'type'             => MENU_LOCAL_TASK,
    'weight'           => -12,
    'menu_name'        => 'user-menu',
  );

I added this code to hook_menu() in a custom module:

  $items['messages/contact-list'] = array(
    'title'            => 'Contact List',
    'page callback'    => 'drupal_goto',
    'page arguments'    => array('messages/contact-list'),
    'access callback'  => 'privatemsg_user_access',
    'access arguments' => array('read privatemsg'),
    'type'             => MENU_LOCAL_TASK,
    'weight'           => 10,
    'menu_name'        => 'user-menu',
  );

However, although this produces no errors, even after clearing the cache multiple times no tab appears anywhere. I tried moving the code from my custom module into the privatemsg module to no effect. I've looked at the documentation for hook_menu() but it still isn't clear to me what I'm doing wrong.