code: def find_inherited_key_completions(rootpath, root_env):
    
    tup = inflate_context_tuple(rootpath, root_env)
    if isinstance(tup, runtime.CompositeTuple):
      keys = set(k for t in tup.tuples[:-1] for k in t.keys())
      return {n: get_completion(tup, n) for n in keys}
    return {}
docs: Return completion keys from INHERITED tuples.
  
    Easiest way to get those is to evaluate the tuple, check if it is a CompositeTuple,
    then enumerate the keys that are NOT in the rightmost tuple.