diff --git a/scripts/memory-mcp.mjs b/scripts/memory-mcp.mjs
old mode 100755
new mode 100644
index 932d085d4..ea2fd57c6
--- a/scripts/memory-mcp.mjs
+++ b/scripts/memory-mcp.mjs
@@ -383,10 +383,12 @@ function createMemoryMcpService(options = {}) {
 
       const isNotification = !hasId;
       if (isNotification) {
+        const params = message.params ?? {};
         if (
           message.method === 'notifications/initialized'
           && initializationRequested
-          && Object.keys(message.params || {}).length === 0
+          && (!Object.prototype.hasOwnProperty.call(params, '_meta') || isRecord(params._meta))
+          && Object.keys(params).every(key => key === '_meta')
         ) {
           initialized = true;
         }
diff --git a/tests/scripts/memory-mcp.test.js b/tests/scripts/memory-mcp.test.js
index 9ba90dd55..bbb43f9bf 100644
--- a/tests/scripts/memory-mcp.test.js
+++ b/tests/scripts/memory-mcp.test.js
@@ -806,6 +806,76 @@ async function main() {
     assert.strictEqual(invalidParams.error.code, -32600);
   });
 
+  for (const [label, params] of [
+    ['omitted params', undefined],
+    ['empty params', {}],
+    ['empty metadata', { _meta: {} }],
+    ['extension metadata', { _meta: { 'example.com/trace': 'sample' } }],
+  ]) {
+    await test(`accepts initialized notifications with ${label}`, async () => {
+      const { createMemoryMcpService } = await import(pathToFileURL(SERVER).href);
+      const service = createMemoryMcpService({ harness: 'claude' });
+      const initialized = await service.handle({
+        jsonrpc: '2.0', id: 1, method: 'initialize',
+        params: {
+          protocolVersion: '2025-11-25', capabilities: {},
+          clientInfo: { name: 'metadata-test', version: '1.0.0' },
+        },
+      });
+      assert.strictEqual(initialized.error, undefined);
+      const notification = await service.handle({
+        jsonrpc: '2.0', method: 'notifications/initialized',
+        ...(params === undefined ? {} : { params }),
+      });
+      assert.strictEqual(notification, null);
+      const listed = await service.handle({ jsonrpc: '2.0', id: 2, method: 'tools/list' });
+      assert.strictEqual(listed.error, undefined);
+      assert.ok(listed.result.tools.some(tool => tool.name === 'memory_search'));
+    });
+  }
+
+  await test('ignores initialized notifications with malformed metadata or unknown params', async () => {
+    const { createMemoryMcpService } = await import(pathToFileURL(SERVER).href);
+    for (const params of [
+      ...[null, [], 'invalid', 1, false].map(_meta => ({ _meta })),
+      { _meta: {}, unexpected: true },
+    ]) {
+      const service = createMemoryMcpService({ harness: 'claude' });
+      await service.handle({
+        jsonrpc: '2.0', id: 1, method: 'initialize',
+        params: {
+          protocolVersion: '2025-11-25', capabilities: {},
+          clientInfo: { name: 'metadata-test', version: '1.0.0' },
+        },
+      });
+      assert.strictEqual(await service.handle({
+        jsonrpc: '2.0', method: 'notifications/initialized', params,
+      }), null);
+      const listed = await service.handle({ jsonrpc: '2.0', id: 2, method: 'tools/list' });
+      assert.strictEqual(listed.error?.code, -32002, JSON.stringify(params));
+    }
+  });
+
+  await test('does not initialize from a metadata notification sent before initialize', async () => {
+    const { createMemoryMcpService } = await import(pathToFileURL(SERVER).href);
+    const service = createMemoryMcpService({ harness: 'claude' });
+    const notification = {
+      jsonrpc: '2.0', method: 'notifications/initialized', params: { _meta: {} },
+    };
+    assert.strictEqual(await service.handle(notification), null);
+    const before = await service.handle({ jsonrpc: '2.0', id: 1, method: 'tools/list' });
+    assert.strictEqual(before.error?.code, -32002);
+    await service.handle({
+      jsonrpc: '2.0', id: 2, method: 'initialize',
+      params: {
+        protocolVersion: '2025-11-25', capabilities: {},
+        clientInfo: { name: 'metadata-test', version: '1.0.0' },
+      },
+    });
+    const after = await service.handle({ jsonrpc: '2.0', id: 3, method: 'tools/list' });
+    assert.strictEqual(after.error?.code, -32002);
+  });
+
   await test('bounds queued transport work under a single-chunk request flood', async () => {
     const {
       MAX_PENDING_MESSAGES,