case "windows":
		return "USERPROFILE"
	case "plan9":
		return "home"
	default:
		return "HOME"
	}
}

// tempEnvName returns the environment variable used by os.TempDir
// to locate the default directory for temporary files.
func tempEnvName() string {
	switch runtime.GOOS {
	case "windows":
		return "TMP"
	case "plan9":

	// with a signal they might fail to clean up some temp files, and we don't
	// want that to cause an "unexpected files" failure at the end of the run.
	cmd.Env = append(slices.Clip(tg.env), tempEnvName()+"="+t.TempDir())

	cmd.SysProcAttr = &syscall.SysProcAttr{
		Setpgid: true,
	}
	cmd.Cancel = func() error {
		pgid := cmd.Process.Pid
		return syscall.Kill(-pgid, syscall.SIGINT)
	}