docs: def _load_build(self):
          """See `pickle.py` in Python's source code."""
          # if the ctor. function (penultimate on the stack) is the `Ref` class...
          if isinstance(self.stack[-2], Ref):
              # Ref.__setstate__ will know it's a remote ref if the state is a tuple
              self.stack[-1] = (self.stack[-1], self.node)
  
              self.load_build()  # continue with the default implementation
  
              # detect our own refs sent back to us
              ref = self.stack[-1]
              if ref.uri.node == self.node.nid:
                  ref.is_local = True
                  ref._cell = self.node.guardian.lookup_cell(ref.uri)
                  # dbg(("dead " if not ref._cell else "") + "local ref detected")
                  del ref.node  # local refs never need access to the node
          else:  # pragma: no cover
              self.load_build()