title: When I use Kubernetes as my agent in Jenkins it will not allow another executor in stage
body: <p>This is a subset of my declarative Jenkinsfile:</p>
  
  <pre><code>pipeline {
      agent {
        kubernetes {
          yamlFile 'pod.yml'
          defaultContainer 'tools'
        }
      }
      stages {
          stage('Init') { // &lt;- this stage executes in Kubernetes and works very well
              steps {
                  sh "echo init"
              }
          }
          stage('Build') {
              agent { label 'B202981' } // &lt;- This wont work; B202981 is computer on my network
              steps {
                  sh "echo build"
              }
          }
      }
  }
  </code></pre>
  
  <p>When this pipelines runs it fails with an exception which you can see here and googling this exception didn't helped me.</p>
  
  <pre><code>java.lang.ClassCastException: hudson.slaves.DumbSlave cannot be cast to org.csanchez.jenkins.plugins.kubernetes.KubernetesSlave
      at org.csanchez.jenkins.plugins.kubernetes.pipeline.ContainerExecDecorator$1.launch(ContainerExecDecorator.java:250)
      at hudson.Launcher$ProcStarter.start(Launcher.java:455)
      at org.jenkinsci.plugins.durabletask.WindowsBatchScript.doLaunch(WindowsBatchScript.java:83)
      at org.jenkinsci.plugins.durabletask.FileMonitoringTask.launchWithCookie(FileMonitoringTask.java:106)
      at org.jenkinsci.plugins.durabletask.FileMonitoringTask.launch(FileMonitoringTask.java:99)
      at org.jenkinsci.plugins.workflow.steps.durable_task.DurableTaskStep$Execution.start(DurableTaskStep.java:317)
      at org.jenkinsci.plugins.workflow.cps.DSL.invokeStep(DSL.java:286)
      at org.jenkinsci.plugins.workflow.cps.DSL.invokeMethod(DSL.java:179)
      at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:122)
      at sun.reflect.GeneratedMethodAccessor23291.invoke(Unknown Source)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:498)
      at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
      at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
      at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
      at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
      at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:42)
      at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
      at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
      at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:160)
      at org.kohsuke.groovy.sandbox.GroovyInterceptor.onMethodCall(GroovyInterceptor.java:23)
      at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:157)
      at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:142)
      at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:158)
      at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:162)
      at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:17)
      at WorkflowScript.runBuildRexx(WorkflowScript:17)
      at WorkflowScript.run(WorkflowScript:77)
      at ___cps.transform___(Native Method)
      at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:86)
      at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:113)
      at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:83)
      at sun.reflect.GeneratedMethodAccessor386.invoke(Unknown Source)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:498)
      at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
      at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:107)
      at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:83)
      at sun.reflect.GeneratedMethodAccessor386.invoke(Unknown Source)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:498)
      at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
      at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:89)
      at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:113)
      at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:83)
      at sun.reflect.GeneratedMethodAccessor386.invoke(Unknown Source)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:498)
      at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
      at com.cloudbees.groovy.cps.impl.ConstantBlock.eval(ConstantBlock.java:21)
      at com.cloudbees.groovy.cps.Next.step(Next.java:83)
      at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:174)
      at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:163)
      at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:129)
      at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:268)
      at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:163)
      at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
      at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:51)
      at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:185)
      at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:405)
      at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$400(CpsThreadGroup.java:96)
      at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:317)
      at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:281)
      at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:67)
      at java.util.concurrent.FutureTask.run(FutureTask.java:266)
      at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:131)
      at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
      at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:59)
      at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
      at java.util.concurrent.FutureTask.run(FutureTask.java:266)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
      at java.lang.Thread.run(Thread.java:748)
  Finished: FAILURE
  </code></pre>
  
  <p>I am using <a href="https://github.com/jenkinsci/kubernetes-plugin" rel="nofollow noreferrer">Kubernetes-plugin for Jenkins</a> so I can use Kubernetes for executing some of my stages. A speciel stage needs to be executed on another executor which is a Windows computer and it seems that if I choose Kubernetes as my root agent then I can't pick other agents for a specific stage.</p>