fix: exclude jdk.jfr classes from transformation to prevent JFR reentrancy corruption (#821)

During JFR event writing (e.g. FileWriteEvent), EventWriter.endEvent() may
trigger class loading of jdk.jfr.internal.Bits on the large-size path.
TtlTransformer intercepts this class loading, and Javassist introspection
side effects (NotFoundException, object allocations) produce nested JFR
events that corrupt the in-progress event buffer, resulting in corrupted
JFR files with invalid event sizes.

Adding jdk.jfr to the package exclusion list prevents this reentrancy.
TTL would never transform JFR classes anyway (they are not executors or
thread pools), so this is a safe no-op filter.

Author: korniltsev-grafanista-yolo-vibecoder239

ttl-agent/src/main/java/com/alibaba/ttl3/agent/TtlTransformer.java

@@ -63,6 +63,11 @@ public final byte[] transform(@Nullable final ClassLoader loader, @Nullable fina
             final ClassInfo classInfo = new ClassInfo(classFile, classFileBuffer, loader);
             if (isClassUnderPackage(classInfo.getClassName(), "com.alibaba.ttl")) return NO_TRANSFORM;
             if (isClassUnderPackage(classInfo.getClassName(), "java.lang")) return NO_TRANSFORM;
+            // Exclude JFR classes to prevent reentrancy corruption in JFR EventWriter.
+            // During event writing, class loading can trigger this transformer, and Javassist
+            // introspection side effects (exceptions, allocations) produce nested JFR events
+            // that corrupt the in-progress event buffer.
+            if (isClassUnderPackage(classInfo.getClassName(), "jdk.jfr")) return NO_TRANSFORM;
 
             if (logClassTransform)
                 logger.info("[TtlTransformer] transforming " + classInfo.getClassName()

ttl2-compatible/src/main/java/com/alibaba/ttl/threadpool/agent/TtlTransformer.java

@@ -64,6 +64,11 @@ public final byte[] transform(@Nullable final ClassLoader loader, @Nullable fina
             final ClassInfo classInfo = new ClassInfo(classFile, classFileBuffer, loader);
             if (isClassUnderPackage(classInfo.getClassName(), "com.alibaba.ttl")) return NO_TRANSFORM;
             if (isClassUnderPackage(classInfo.getClassName(), "java.lang")) return NO_TRANSFORM;
+            // Exclude JFR classes to prevent reentrancy corruption in JFR EventWriter.
+            // During event writing, class loading can trigger this transformer, and Javassist
+            // introspection side effects (exceptions, allocations) produce nested JFR events
+            // that corrupt the in-progress event buffer.
+            if (isClassUnderPackage(classInfo.getClassName(), "jdk.jfr")) return NO_TRANSFORM;
 
             if (logClassTransform)
                 logger.info("[TtlTransformer] transforming " + classInfo.getClassName()