Jenkins Configuration and Declarative Pipelines Questions

# install deps, run tests, build artifact
git rev-parse --abbrev-ref HEAD
./gradlew clean build

pipeline {
  agent any
  stages {
    stage('Parallel work') {
      steps {
        script {
          // parallel supports a map of closures; pass failFast: true as an extra arg
          parallel(
            failFast: true,
            "job-A": {
              try {
                echo "Start A"
                // simulate work/failure
                sh 'sleep 10; exit 0'
              } finally {
                // guaranteed cleanup for branch A
                echo "Cleanup A (always runs)"
              }
            },
            "job-B": {
              try {
                echo "Start B"
                // simulate a failing branch
                sh 'sleep 2; exit 1'
              } finally {
                // guaranteed cleanup for branch B
                echo "Cleanup B (always runs)"
              }
            },
            "job-C": {
              try {
                echo "Start C"
                sh 'sleep 20; exit 0'
              } finally {
                echo "Cleanup C (always runs)"
              }
            }
          )
        }
      }
    }
  }
  post {
    always {
      echo "Global cleanup / notifications run regardless of result"
    }
  }
}

pipeline {
  agent none
  options { skipDefaultCheckout(true) }
  stages {
    stage('Matrix build & test') {
      matrix {
        axes {
          axis {
            name 'JDK'
            values '8','11'
          }
          axis {
            name 'OS'
            values 'linux','windows'
          }
        }
        agent {
          // choose docker for linux, labeled node for windows
          label 'unused'
          docker {
            image (OS == 'linux' ? "openjdk:${JDK}-jdk" : null)
            args '-u root:root'
          }
        }
        stages {
          stage('Checkout') {
            steps {
              checkout scm
            }
          }
          stage('Build') {
            steps {
              script {
                if (OS == 'windows') {
                  // run on windows agent
                  node('windows') {
                    checkout scm
                    bat "mvn -B -DskipTests package"
                    stash includes: '**/target/*.jar', name: "artifact-${OS}-${JDK}"
                    archiveArtifacts artifacts: "target/*.jar", fingerprint: true, onlyIfSuccessful: true
                  }
                  // prevent further steps in this agent block
                  sh 'echo windows build done' // noop for declarative flow
                } else {
                  // linux in docker agent
                  sh "mvn -B -DskipTests package"
                  stash includes: '**/target/*.jar', name: "artifact-${OS}-${JDK}"
                  archiveArtifacts artifacts: "target/*.jar", fingerprint: true, onlyIfSuccessful: true
                }
              }
            }
          }
          stage('Test') {
            steps {
              script {
                // Demonstrate unstash on same/different agent for testing
                if (OS == 'windows') {
                  node('windows') {
                    unstash "artifact-${OS}-${JDK}"
                    bat "mvn -B test"
                  }
                } else {
                  // linux docker agent runs tests
                  unstash "artifact-${OS}-${JDK}"
                  sh "mvn -B test"
                }
              }
            }
          }
        }
        post {
          success {
            echo "Matrix cell ${OS}/${JDK} succeeded"
          }
        }
      } // matrix
    } // stage
  } // stages
}