Fix @PreDestroy ClassNotFoundException from premature ClassRealm disposal (PR #11825)

Cherry-pick from fix/realm-cache-dispose-ordering branch.

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

Author: gnodet

impl/maven-core/src/main/java/org/apache/maven/plugin/DefaultExtensionRealmCache.java

@@ -149,6 +149,6 @@ public void register(MavenProject project, Key key, CacheRecord record) {
 
     @Override
     public void dispose() {
-        flush();
+        cache.clear();
     }
 }

impl/maven-core/src/main/java/org/apache/maven/plugin/DefaultPluginRealmCache.java

@@ -215,6 +215,6 @@ public void register(MavenProject project, Key key, CacheRecord record) {
 
     @Override
     public void dispose() {
-        flush();
+        cache.clear();
     }
 }

impl/maven-core/src/main/java/org/apache/maven/project/DefaultProjectRealmCache.java

@@ -125,6 +125,6 @@ public void register(MavenProject project, Key key, CacheRecord record) {
 
     @Override
     public void dispose() {
-        flush();
+        cache.clear();
     }
 }

impl/maven-core/src/test/java/org/apache/maven/plugin/DefaultRealmCacheDisposeTest.java

@@ -0,0 +1,85 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.plugin;
+
+import java.util.List;
+
+import org.apache.maven.artifact.Artifact;
+import org.codehaus.plexus.classworlds.ClassWorld;
+import org.codehaus.plexus.classworlds.realm.ClassRealm;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Verifies that dispose() does not dispose ClassRealms prematurely.
+ * <p>
+ * Plexus Disposable.dispose() runs before Sisu's @PreDestroy callbacks.
+ * If dispose() disposes ClassRealms, beans loaded from those realms will
+ * get ClassNotFoundException when their @PreDestroy methods execute.
+ * dispose() should only clear the cache map; flush() should dispose realms.
+ *
+ * @see <a href="https://github.com/apache/maven/issues/10571">MNG-8572</a>
+ */
+class DefaultRealmCacheDisposeTest {
+
+    @Test
+    void disposeDoesNotDisposeClassRealms() throws Exception {
+        ClassWorld world = new ClassWorld();
+        ClassRealm realm = world.newRealm("test-plugin-realm");
+
+        DefaultPluginRealmCache cache = new DefaultPluginRealmCache();
+        PluginRealmCache.CacheRecord record = new PluginRealmCache.CacheRecord(realm, List.<Artifact>of());
+        cache.cache.put(new TestKey(), record);
+
+        cache.dispose();
+
+        assertTrue(cache.cache.isEmpty(), "dispose() should clear the cache");
+        assertNotNull(world.getClassRealm("test-plugin-realm"), "dispose() should NOT dispose the ClassRealm");
+    }
+
+    @Test
+    void flushDisposesClassRealms() throws Exception {
+        ClassWorld world = new ClassWorld();
+        ClassRealm realm = world.newRealm("test-plugin-realm-flush");
+
+        DefaultPluginRealmCache cache = new DefaultPluginRealmCache();
+        PluginRealmCache.CacheRecord record = new PluginRealmCache.CacheRecord(realm, List.<Artifact>of());
+        cache.cache.put(new TestKey(), record);
+
+        cache.flush();
+
+        assertTrue(cache.cache.isEmpty(), "flush() should clear the cache");
+        assertNull(world.getClassRealm("test-plugin-realm-flush"), "flush() SHOULD dispose the ClassRealm");
+    }
+
+    private static class TestKey implements PluginRealmCache.Key {
+        @Override
+        public int hashCode() {
+            return 1;
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            return obj instanceof TestKey;
+        }
+    }
+}