code: def iter_doc_filepaths(self, **kwargs):
          
          for shard in self._shards:
              for doc_id, blob in shard.iter_doc_filepaths(**kwargs):
                  yield doc_id, blob
docs: Generator that iterates over all detected documents.
          and returns the filesystem path to each doc.
          Order is by shard, but arbitrary within shards.
          @TEMP not locked to prevent doc creation/deletion