?:

gistfile1.txt

pipeline {
    agent none
    environment { 
        AGENT_LABEL = 'builder'
    }
    stages {
        stage('Example') {
            agent { label "${AGENT_LABEL}" }
            steps {
                sh 'printenv'
            }
        }
    }
}

Resaults with: groovy.lang.MissingPropertyException: No such property: AGENT_LABEL for class: groovy.lang.Binding

If I take any of the vars returned by "sh 'printenv'" command and use them as label - they work.