def add(path, forced: false)
      return metadata[path] if metadata.key?(path)
      metadata[path] = {
        seen_before: false,
        dynamic: !File.exist?(site.in_source_dir(path)),
        last_modified: file_mtime_of(path),
        dependencies: Set.new,
        forced: forced,
      }
    end
def add(path, forced: false)
      return metadata[path] if metadata.key?(path)
      metadata[path] = {
        seen_before: false,
        dynamic: !File.exist?(site.in_source_dir(path)),
        last_modified: file_mtime_of(path),
        dependencies: Set.new,
        forced: forced,
      }
    end
--
 seen_before address a logical race that happens
   incide of Jekyll.  Dependencies are added before
   dependents, which is not good at all.
 --