docs: def files(self):
          """Set of found binary files output by StagYY."""
          if self._rundir['ls'] is UNDETERMINED:
              out_stem = pathlib.Path(self.par['ioin']['output_file_stem'] + '_')
              out_dir = self.path / out_stem.parent
              if out_dir.is_dir():
                  self._rundir['ls'] = set(out_dir.iterdir())
              else:
                  self._rundir['ls'] = set()
          return self._rundir['ls']