0. Jenkins slave run for couple days.
1. Git fetches failed one day suddenly.
2. Complaint Putty class java.lang.NoClassDefFoundError. although it exists under ~/.jenkins/cache/jars in that slave.

I assume the jenkins cache is messed up somehow or at least slave process suddenly has wrong memory of whats in the cache.
so I did below test.
1. disconnect the jenkins slave to kill slave java process.
2. rm -rf ~/.jenkins/cache/jars.
3. bring jenkins slave back online(launche method ssh)
4. I did see the ~/.jenkins/cache/jars filled with jars. but it does not include
PuTTYKey and it does not even include class JavaVMArguments.class.
5. if manually copied jar files in another functional jenkins slave to the cache and re-launche agent, those jars/classes still cant be recognized by slave java process.

Note: the master jvm uses jdk1.7.75, the slave uses jdk1.7.79.

12:42:12 - ERROR: Error fetching remote repo 'origin'
12:42:12 - hudson.plugins.git.GitException: Failed to fetch from git@XXX:YYY.git
12:42:12 - at hudson.plugins.git.GitSCM.fetchFrom(GitSCM.java:735)
12:42:12 - at hudson.plugins.git.GitSCM.retrieveChanges(GitSCM.java:983)
12:42:12 - at hudson.plugins.git.GitSCM.checkout(GitSCM.java:1016)
12:42:12 - at hudson.scm.SCM.checkout(SCM.java:488)
12:42:12 - at hudson.model.AbstractProject.checkout(AbstractProject.java:1257)
12:42:12 - at hudson.model.AbstractBuild$AbstractBuildExecution.defaultCheckout(AbstractBuild.java:622)
12:42:12 - at jenkins.scm.SCMCheckoutStrategy.checkout(SCMCheckoutStrategy.java:86)
12:42:12 - at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:528)
12:42:12 - at hudson.model.Run.execute(Run.java:1745)
12:42:12 - at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
12:42:12 - at hudson.model.ResourceController.execute(ResourceController.java:89)
12:42:12 - at hudson.model.Executor.run(Executor.java:240)
12:42:12 - Caused by: hudson.plugins.git.GitException: java.io.IOException: Remote call on a004999.com failed
12:42:12 - at org.jenkinsci.plugins.gitclient.RemoteGitImpl$CommandInvocationHandler.execute(RemoteGitImpl.java:172)
12:42:12 - at sun.reflect.GeneratedMethodAccessor165.invoke(Unknown Source)
12:42:12 - at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
12:42:12 - at java.lang.reflect.Method.invoke(Method.java:606)
12:42:12 - at org.jenkinsci.plugins.gitclient.RemoteGitImpl$CommandInvocationHandler.invoke(RemoteGitImpl.java:131)
12:42:12 - at com.sun.proxy.$Proxy48.execute(Unknown Source)
12:42:12 - at hudson.plugins.git.GitSCM.fetchFrom(GitSCM.java:733)
12:42:12 - ... 11 more
12:42:12 - Caused by: java.io.IOException: Remote call on a004999.com failed
12:42:12 - at hudson.remoting.Channel.call(Channel.java:760)
12:42:12 - at org.jenkinsci.plugins.gitclient.RemoteGitImpl$CommandInvocationHandler.execute(RemoteGitImpl.java:145)
12:42:12 - ... 17 more
12:42:12 - Caused by: java.lang.NoClassDefFoundError: org/kohsuke/putty/PuTTYKey
12:42:12 - at com.cloudbees.jenkins.plugins.sshcredentials.impl.BasicSSHUserPrivateKey.getPrivateKeys(BasicSSHUserPrivateKey.java:132)
12:42:12 - at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.createSshKeyFile(CliGitAPIImpl.java:1417)
12:42:12 - at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandWithCredentials(CliGitAPIImpl.java:1295)
12:42:12 - at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.access$300(CliGitAPIImpl.java:86)
12:42:12 - at org.jenkinsci.plugins.gitclient.CliGitAPIImpl$1.execute(CliGitAPIImpl.java:324)
12:42:12 - at org.jenkinsci.plugins.gitclient.RemoteGitImpl$CommandInvocationHandler$1.call(RemoteGitImpl.java:152)
12:42:12 - at org.jenkinsci.plugins.gitclient.RemoteGitImpl$CommandInvocationHandler$1.call(RemoteGitImpl.java:145)
12:42:12 - at hudson.remoting.UserRequest.perform(UserRequest.java:121)
12:42:12 - at hudson.remoting.UserRequest.perform(UserRequest.java:49)
12:42:12 - at hudson.remoting.Request$2.run(Request.java:324)
12:42:12 - at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:68)
12:42:12 - at java.util.concurrent.FutureTask.run(FutureTask.java:262)
12:42:12 - at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
12:42:12 - at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
12:42:12 - at java.lang.Thread.run(Thread.java:745)
12:42:12 - at ......remote call to a004999.com(Native Method)
12:42:12 - at hudson.remoting.Channel.attachCallSiteStackTrace(Channel.java:1356)
12:42:12 - at hudson.remoting.UserResponse.retrieve(UserRequest.java:221)
12:42:12 - at hudson.remoting.Channel.call(Channel.java:752)
12:42:12 - ... 18 more
12:42:12 - ERROR: Error fetching remote repo 'origin'
12:42:12 - Recording test results