The containing class is available as OS\posix_spawn_file_actions_addchdir_np
in the www repository.
protected function forkAndExecveDecorator(
HH\Lib\_Private\_OS\TForkAndExecve $fork_and_execve,
): HH\Lib\_Private\_OS\TForkAndExecve;
HH\Lib\_Private\_OS\TForkAndExecve $fork_and_execve
HH\Lib\_Private\_OS\TForkAndExecve