build/CheckFiles.java introduced in 27+5 needs updating for Valhalla:
----------------
  visiting file:c:\\ade\\mesos\\work_dir\\jib-master\\install\\2026-01-20-0702527.david.simms.valhalla_merging\\windows-x64.jdk\\jdk-27\\lib\\valueclasses\\java.base-valueclasses.jar
  --> ERROR this file is not allowed:java.base-valueclasses.jar
Bin directory scan successful.
----------System.err:(10/504)----------
java.lang.Error: lib dir scan failed
at CheckFiles.main(CheckFiles.java:122)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
at java.base/java.lang.reflect.Method.invoke(Method.java:565)
at com.sun.javatest.regtest.agent.MainActionHelper$AgentVMRunnable.run(MainActionHelper.java:335)
at java.base/java.lang.Thread.run(Thread.java:1516)

JavaTest Message: Test threw exception: java.lang.Error
JavaTest Message: shutting down test

result: Failed. Execution failed: `main' threw exception: java.lang.Error: lib dir scan failed
----------------

The cause for this is that the valueclass handling rules in CompileJavaModules.gmk leave unnecessary temporary files, but they could also be improved in terms of how the rules are constructed and commented.