code: func (p *Pod) AppExitCode(appName string) (int, error) {
  	stage1RootfsPath, err := p.Stage1RootfsPath()
  	if err != nil {
  		return -1, err
  	}
  
  	statusFile := common.AppStatusPathFromStage1Rootfs(stage1RootfsPath, appName)
  	return p.readIntFromFile(statusFile)
  }
docs: // AppExitCode returns the app's exit code.
  // It returns an error if the exit code file doesn't exit or the content of the file is invalid.