Custom Entities Do Not Show in Site Studio as a Reference Entity

Issue

A custom entity has been created but is not showing up as a reference entity in Site Studio, in the entity browser element.

Use case: You prefer to load entities by reference in a 'drupal-style' method, if Site Studio's 'custom element' interface feels limited.

Resolution

Set the entity annotation flag common_reference_target = TRUE

This makes the custom entity available to entity reference fields.

Re-save the Site Studio settings, styles and templates by running drush cohesion:rebuild in the Drupal docroot using a CLI and clear Drupal caches.