This is probably a one-line implements PhabricatorMentionableInterface on PholioMock.

In the Pholio application, the Pholio Paste object is defined in the PholioMock class. In the class definition, you can see PholioMock extends the PholioDAO class and implements a bunch of interfaces. Mentions can be implemented by adding PhabricatorMentionableInterface along with the others. To test:

• Create a Pholio Mock
• Open an existing object like a Maniphest task
• Add a comment that contains a mention of the Pholio Mock (either M123 or {M123} should work)
• Refresh the Pholio Mock detail view
• RESULT: Pholio Mock timeline feed should have an entry for a mention of the mock