* Public holidays generate timesheet entries carrying ``global_leave_id``
  instead of ``holiday_id``. Neither policy applies to them: they do not belong
  to a single employee and there is no balance to restore. They are deleted
  with the sheet like any other entry, and they are removed on their own when
  the public holiday itself is deleted, through the ``ondelete='cascade'`` of
  the field.

* The ``cancel`` policy refuses, resets and deletes the time off request. An
  installation that wants to keep a history of the cancelled requests would
  stop at the refusal, which is already where the days are restored to the
  balance. It is a known variant and it is not implemented.

* The confirmation wizard reads the time off requests in ``sudo`` under the
  ``cancel`` policy, because a timesheet manager entitled to delete the sheet
  of another employee is not necessarily entitled to read that employee's time
  off.