code: func Context(th *starlark.Thread) context.Context {
  	if ctx := th.Local(threadCtxKey); ctx != nil {
  		return ctx.(context.Context)
  	}
  	panic("not an Interpreter thread, no context in its locals")
  }
docs: // Context returns a context of the thread created through Interpreter.
  //
  // Panics if the Starlark thread wasn't created through Interpreter.Thread().