Clear context class loader from started threads

[laurit]

Thread inherits context class loader from the thread that started it. This could be problematic when a thread is started from an application thread. For example with the StrictContextStorage (which is not used by default) some agent tests run on tomcat produce the following warning

Jul 14, 2025 4:08:02 PM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
WARNING: The web application [app] appears to have started a thread named [weak-ref-cleaner-strictcontextstorage] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 java.base/jdk.internal.misc.Unsafe.park(Native Method)
 java.base/java.util.concurrent.locks.LockSupport.park(LockSupport.java:371)
 java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:519)
 java.base/java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3780)
 java.base/java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3725)
 java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1707)
 java.base/java.lang.ref.ReferenceQueue.await(ReferenceQueue.java:67)
 java.base/java.lang.ref.ReferenceQueue.remove0(ReferenceQueue.java:158)
 java.base/java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:234)
 io.opentelemetry.context.StrictContextStorage$PendingScopes.run(StrictContextStorage.java:270)
 java.base/java.lang.Thread.run(Thread.java:1583)

Basically this tells that even when you undeploy the application the resources can't be freed because there is thread that has a reference to the application class loader.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.00%. Comparing base (8009415) to head (41415e5).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #7488   +/-   ##
=========================================
  Coverage     90.00%   90.00%           
  Complexity     7078     7078           
=========================================
  Files           803      803           
  Lines         21405    21408    +3     
  Branches       2086     2086           
=========================================
+ Hits          19265    19268    +3     
  Misses         1477     1477           
  Partials        663      663           

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[jkwatson]

this seems fine. are there any downsides to removing the context class loader, though? What is it generally used for?