docs: def clear_stalled_files(self):
          """Scan upload directory and delete stalled files.
  
          Stalled files are files uploaded more than
          `DELETE_STALLED_AFTER` seconds ago.
          """
          # FIXME: put lock in directory?
          CLEAR_AFTER = self.config["DELETE_STALLED_AFTER"]
          minimum_age = time.time() - CLEAR_AFTER
  
          for user_dir in self.UPLOAD_DIR.iterdir():
              if not user_dir.is_dir():
                  logger.error("Found non-directory in upload dir: %r", bytes(user_dir))
                  continue
  
              for content in user_dir.iterdir():
                  if not content.is_file():
                      logger.error(
                          "Found non-file in user upload dir: %r", bytes(content)
                      )
                      continue
  
                  if content.stat().st_ctime < minimum_age:
                      content.unlink()