code: def _get_active_contract_at_offset(self, root_symbol, dt, offset):
          
          oc = self.asset_finder.get_ordered_contracts(root_symbol)
          session = self.trading_calendar.minute_to_session_label(dt)
          front = oc.contract_before_auto_close(session.value)
          back = oc.contract_at_offset(front, 1, dt.value)
          if back is None:
              return front
          primary = self._active_contract(oc, front, back, session)
          return oc.contract_at_offset(primary, offset, session.value)
docs: For the given root symbol, find the contract that is considered active
          on a specific date at a specific offset.