The bundle deeply integrates Bricks by 20steps including Symfony 3 with Drupal7 and vice versa. This is done without altering Drupal's core.
When this bundle is activated, the Symfony 3 console will have the Drupal 7.x libraries autoloaded. So, it makes possible the use of Drupal libraries from your Symfony 3 command.
# "symfony__" during a migration generation.
The PERMISSION_DRUPAL_ACCESS_ADMINISTRATION_PAGES is translate in "access administration pages" and used with user_access and global Drupal user.
If you want use you "personal access" permission, use role PERMISSION_DRUPAL_PERSONAL_ACCESS for example.
It is not possible to use Symfony native class to manage session as Drupal initializes its own session handler and there is no way to change this.
You can note the Web Debug Toolbar of Symfony at the bottom ;-).