docs: def _ensure_pgrp(self):
          """Ensures that the pgrp file is present and up to date. There have
          been production cases where the file was lost or not
          immediately emitted due to disk space issues.
          """
          if not LAST_PGRP_PATH:  # global
              return
          try:
              with open(LAST_PGRP_PATH, 'w') as f:
                  f.write(str(os.getpgrp()) + "\n")
          except IOError:
              # raised if no permissions or disk space
              pass