///   * Must set `status` to `TF_RESOURCE_EXHAUSTED` if fewer than `n` bytes
  ///     have been written, potentially due to quota/disk space.
  ///   * Might use any other error value for `status` to signal other errors.
  void (*append)(const TF_WritableFile* file, const char* buffer, size_t n,
                 TF_Status* status);

  /// Returns the current write position in `*file`.
  ///