Running a Jenkins post stage in a docker container

gistfile1.txt

pipeline {
    agent none
    stages {
        stage('Step1'){
            agent { docker { image 'simonmcc/hashicorp-pipeline:latest' } }
            steps {
                echo "Hello from Step1"
            }
        }
        stage('Stage2') {
            steps {
                script { 
                    echo "this is a scripted fragment" 
                    docker.image("simonmcc/hashicorp-pipeline:latest").inside {
                        sh 'ls'
                    }
                }
            }
        }
    }
    post {
        always {
            echo "post-always"
            script { 
                echo "this is a scripted fragment" 
                docker.image("simonmcc/hashicorp-pipeline:latest").inside {
                    sh 'ls'
                }
            }
        }
    }
}