Fix trySetAccessible() caching bug causing Field inaccessibility

WeakHashMap uses equals()-based lookup, but Field.equals() matches by
declaring class + name + type, not identity. When getDeclaredFields()
was called with different predicates, the JVM returned different Field
instances for the same logical field. The cache returned TRUE for the
second instance (via equals match), but setAccessible(true) was never
called on it, leaving it inaccessible. This caused Traverser to silently
skip inaccessible fields, breaking GraphComparator.applyDelta().

Fix: only cache FALSE (failures) to avoid expensive repeated exceptions.
setAccessible(true) on an already-accessible field is a cheap no-op.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jdereg

src/main/java/com/cedarsoftware/util/ClassUtilities.java

@@ -2785,23 +2785,19 @@ private static Object invokeConstructorWithPlan(Converter converter, Object[] su
         Collections.synchronizedMap(new WeakHashMap<>());
 
     static void trySetAccessible(AccessibleObject object) {
-        // Check cache first to avoid repeated failed attempts
-        Boolean prev = accessibilityCache.get(object);
-        if (Boolean.FALSE.equals(prev)) {
-            // Known to fail under current VM/module setup – skip the throwing call
-            // This reduces noisy exceptions on hot paths (constructor/method selection loops) 
-            // in JPMS-sealed modules
+        // Check cache for known failures only. We only cache FALSE (failures) to avoid
+        // expensive repeated exception throwing on JPMS-sealed modules. We do NOT cache
+        // TRUE because WeakHashMap uses equals()-based lookup, and Field.equals() matches
+        // by declaring class + name + type. Different Field instances for the same logical
+        // field (from separate getDeclaredFields() calls) would incorrectly share a TRUE
+        // cache entry, causing the second instance to never get setAccessible(true) called.
+        // Calling setAccessible(true) on an already-accessible field is a cheap no-op.
+        if (Boolean.FALSE.equals(accessibilityCache.get(object))) {
             return;
         }
-        if (Boolean.TRUE.equals(prev)) {
-            // Already accessible, no need to set again
-            return;
-        }
-        
-        // Not in cache, attempt to set accessible
+
         try {
             object.setAccessible(true);
-            accessibilityCache.put(object, Boolean.TRUE);
         } catch (SecurityException e) {
             accessibilityCache.put(object, Boolean.FALSE);
             if (LOG.isLoggable(Level.FINE)) {