fix: Apply CPU throttling to secondary CDP session

src/DevtoolsUtils.ts

@@ -9,6 +9,7 @@ import {Mutex} from './Mutex.js';
 import {DevTools} from './third_party/index.js';
 import type {
   Browser,
+  CDPSession,
   ConsoleMessage,
   Page,
   Protocol,
@@ -49,6 +50,8 @@ export interface TargetUniverse {
   /** The DevTools target corresponding to the puppeteer Page */
   target: DevTools.Target;
   universe: DevTools.Foundation.Universe.Universe;
+  /** The secondary session created for this page */
+  session: CDPSession;
 }
 export type TargetUniverseFactoryFn = (page: Page) => Promise<TargetUniverse>;
 
@@ -158,7 +161,7 @@ const DEFAULT_FACTORY: TargetUniverseFactoryFn = async (page: Page) => {
     undefined,
     connection,
   );
-  return {target, universe};
+  return {target, universe, session};
 };
 
 // We don't want to pause any DevTools universe session ever on the MCP side.

src/McpContext.ts

@@ -329,11 +329,22 @@ export class McpContext implements Context {
       newSettings.networkConditions = options.networkConditions;
     }
 
+    const secondarySession = this.getDevToolsUniverse(mcpPage)?.session;
     if (!options.cpuThrottlingRate) {
       await page.emulateCPUThrottling(1);
+      if (secondarySession) {
+        await secondarySession.send('Emulation.setCPUThrottlingRate', {
+          rate: 1,
+        });
+      }
       delete newSettings.cpuThrottlingRate;
     } else {
       await page.emulateCPUThrottling(options.cpuThrottlingRate);
+      if (secondarySession) {
+        await secondarySession.send('Emulation.setCPUThrottlingRate', {
+          rate: options.cpuThrottlingRate,
+        });
+      }
       newSettings.cpuThrottlingRate = options.cpuThrottlingRate;
     }
 
@@ -481,7 +492,7 @@ export class McpContext implements Context {
       page.networkConditions,
     );
     page.pptrPage.setDefaultNavigationTimeout(
-      NAVIGATION_TIMEOUT * networkMultiplier,
+      NAVIGATION_TIMEOUT * networkMultiplier * cpuMultiplier,
     );
   }
 

tests/tools/emulation.test.ts

@@ -6,7 +6,7 @@
 
 import assert from 'node:assert';
 import type {IncomingHttpHeaders} from 'node:http';
-import {beforeEach, describe, it} from 'node:test';
+import {beforeEach, describe, it, mock} from 'node:test';
 
 import {emulate} from '../../src/tools/emulation.js';
 import {
@@ -209,6 +209,36 @@ describe('emulation', () => {
       });
     });
 
+    it('applies cpu throttling to secondary session', async () => {
+      await withMcpContext(async (response, context) => {
+        const mcpPage = context.getSelectedMcpPage();
+        const universe = context.getDevToolsUniverse(mcpPage);
+        assert.ok(universe);
+
+        const sendSpy = mock.method(universe.session, 'send');
+
+        await emulate.handler(
+          {
+            params: {
+              cpuThrottlingRate: 4,
+            },
+            page: mcpPage,
+          },
+          response,
+          context,
+        );
+
+        assert.ok(sendSpy.mock.calls.length > 0);
+        const cpuCall = sendSpy.mock.calls.find(
+          call => call.arguments[0] === 'Emulation.setCPUThrottlingRate',
+        );
+        assert.ok(cpuCall);
+        assert.deepStrictEqual(cpuCall.arguments[1], {rate: 4});
+
+        sendSpy.mock.restore();
+      });
+    });
+
     it('disables cpu throttling', async () => {
       await withMcpContext(async (response, context) => {
         await context.emulate({