How do I include a required context in a ctools content type plugin?
You can define the required context in the plugin definition array. Use the 'required context' key and the ctools_context_required class.

Here are a few lines of stripped down code you can find in the CTools Plugin Example module:

/**
 * Plugins are described by creating a $plugin array which will be used
 * by the system that includes this file.
 */
$plugin = array(
  'title' =&gt; t('Simplecontext content type'),
  'description' =&gt; t('Simplecontext content type - works with a simplecontext context.'),
  'required context' =&gt; new ctools_context_required(t('Simplecontext'), 'simplecontext'),
);