diff --git a/web/src/services/clusterService.test.ts b/web/src/services/clusterService.test.ts
new file mode 100644
index 00000000..a858a727
--- /dev/null
+++ b/web/src/services/clusterService.test.ts
@@ -0,0 +1,64 @@
+/*
+ * 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.
+ */
+
+import { describe, expect, it, vi } from 'vitest';
+
+vi.mock('../config', () => ({
+  USE_MOCK: true,
+  API_BASE_URL: '/api',
+}));
+
+import { getCluster, listClusters } from './clusterService';
+
+describe('clusterService mock clusters', () => {
+  it('returns defensive copies from cluster detail reads', async () => {
+    const cluster = await getCluster('cluster-prod');
+    const originalBrokerStatus = cluster.brokers[0].status;
+    const originalProxyConnections = cluster.proxies[0].connections;
+    const originalNameServerAddr = cluster.nameServers[0].addr;
+    const originalFlushDiskType = cluster.config.flushDiskType;
+    const originalFirstTps = cluster.tpsHistory[0];
+
+    cluster.brokers[0].status = 'offline';
+    cluster.proxies[0].connections = 0;
+    cluster.nameServers[0].addr = '127.0.0.1:9876';
+    cluster.config.flushDiskType = 'ASYNC_FLUSH';
+    cluster.tpsHistory[0] = 0;
+
+    const fresh = await getCluster('cluster-prod');
+
+    expect(fresh.brokers[0].status).toBe(originalBrokerStatus);
+    expect(fresh.proxies[0].connections).toBe(originalProxyConnections);
+    expect(fresh.nameServers[0].addr).toBe(originalNameServerAddr);
+    expect(fresh.config.flushDiskType).toBe(originalFlushDiskType);
+    expect(fresh.tpsHistory[0]).toBe(originalFirstTps);
+  });
+
+  it('does not share nested references between list and detail reads', async () => {
+    const [listed] = await listClusters();
+    const detail = await getCluster(listed.id);
+
+    expect(detail).toEqual(listed);
+    expect(detail).not.toBe(listed);
+    expect(detail.brokers).not.toBe(listed.brokers);
+    expect(detail.brokers[0]).not.toBe(listed.brokers[0]);
+    expect(detail.proxies).not.toBe(listed.proxies);
+    expect(detail.nameServers).not.toBe(listed.nameServers);
+    expect(detail.config).not.toBe(listed.config);
+    expect(detail.tpsHistory).not.toBe(listed.tpsHistory);
+  });
+});
diff --git a/web/src/services/clusterService.ts b/web/src/services/clusterService.ts
index d758dc6a..fd9fcc75 100644
--- a/web/src/services/clusterService.ts
+++ b/web/src/services/clusterService.ts
@@ -8,33 +8,37 @@ const mockCertStore: K8sCertInfo[] = mockK8sCerts.map((cert) => ({
   san: [...cert.san],
 }));
 
+function copyCluster(cluster: ClusterInfo): ClusterInfo {
+  return {
+    id: cluster.id,
+    name: cluster.name,
+    nsClusterName: cluster.nsClusterName,
+    type: cluster.type,
+    endpoint: cluster.endpoint,
+    status: cluster.status,
+    version: cluster.version,
+    brokers: cluster.brokers.map((broker) => ({ ...broker })),
+    proxies: cluster.proxies.map((proxy) => ({ ...proxy })),
+    nameServers: cluster.nameServers.map((nameServer) => ({ ...nameServer })),
+    config: { ...cluster.config },
+    topicCount: cluster.topicCount,
+    groupCount: cluster.groupCount,
+    tpsHistory: [...cluster.tpsHistory],
+  };
+}
+
 export async function listClusters(): Promise<ClusterInfo[]> {
   if (USE_MOCK) {
-    return clusters.map((c) => ({
-      id: c.id,
-      name: c.name,
-      nsClusterName: c.nsClusterName,
-      type: c.type,
-      endpoint: c.endpoint,
-      status: c.status,
-      version: c.version,
-      brokers: c.brokers.map((broker) => ({ ...broker })),
-      proxies: c.proxies.map((proxy) => ({ ...proxy })),
-      nameServers: c.nameServers.map((nameServer) => ({ ...nameServer })),
-      config: { ...c.config },
-      topicCount: c.topicCount,
-      groupCount: c.groupCount,
-      tpsHistory: [...c.tpsHistory],
-    }));
+    return clusters.map(copyCluster);
   }
   return clusterApi.listClusters();
 }
 
-export async function getCluster(id: string) {
+export async function getCluster(id: string): Promise<ClusterInfo> {
   if (USE_MOCK) {
-    const c = clusters.find((c) => c.id === id);
-    if (!c) throw new Error('Cluster not found');
-    return c;
+    const cluster = clusters.find((item) => item.id === id);
+    if (!cluster) throw new Error('Cluster not found');
+    return copyCluster(cluster);
   }
   return clusterApi.getCluster(id);
 }