diff --git a/packages/web-integration/src/puppeteer/agent-launcher.ts b/packages/web-integration/src/puppeteer/agent-launcher.ts
index 7c1e2e4c0..3ee35e0a8 100644
--- a/packages/web-integration/src/puppeteer/agent-launcher.ts
+++ b/packages/web-integration/src/puppeteer/agent-launcher.ts
@@ -36,9 +36,7 @@ export async function launchPuppeteerPage(
   // prepare the environment
   const ua = target.userAgent || defaultUA;
   let width = defaultViewportWidth;
-  let preferMaximizedWindow = true;
   if (target.viewportWidth) {
-    preferMaximizedWindow = false;
     assert(
       typeof target.viewportWidth === 'number',
       'viewportWidth must be a number',
@@ -48,7 +46,6 @@ export async function launchPuppeteerPage(
   }
   let height = defaultViewportHeight;
   if (target.viewportHeight) {
-    preferMaximizedWindow = false;
     assert(
       typeof target.viewportHeight === 'number',
       'viewportHeight must be a number',
@@ -61,7 +58,6 @@ export async function launchPuppeteerPage(
   }
   let dpr = defaultViewportScale;
   if (target.viewportScale) {
-    preferMaximizedWindow = false;
     assert(
       typeof target.viewportScale === 'number',
       'viewportScale must be a number',
@@ -76,9 +72,7 @@ export async function launchPuppeteerPage(
   };
 
   const headed = preference?.headed || preference?.keepWindow;
-
-  // only maximize window in headed mode
-  preferMaximizedWindow = preferMaximizedWindow && !!headed;
+  const windowSizeArg = `--window-size=${width},${height + (headed ? 200 : 0)}`; // add 200px for the address bar in headed mode
 
   // launch the browser
   if (headed && process.env.CI === '1') {
@@ -94,9 +88,7 @@ export async function launchPuppeteerPage(
     '--disable-features=PasswordLeakDetection',
     '--disable-save-password-bubble',
     `--user-agent="${ua}"`,
-    preferMaximizedWindow
-      ? '--start-maximized'
-      : `--window-size=${width},${height + 200}`, // add 200px for the address bar
+    windowSizeArg,
   ];
 
   launcherDebug(
diff --git a/packages/web-integration/tests/unit-test/puppeteer/agent-launcher.test.ts b/packages/web-integration/tests/unit-test/puppeteer/agent-launcher.test.ts
new file mode 100644
index 000000000..a37e19292
--- /dev/null
+++ b/packages/web-integration/tests/unit-test/puppeteer/agent-launcher.test.ts
@@ -0,0 +1,64 @@
+import {
+  defaultViewportHeight,
+  defaultViewportWidth,
+  launchPuppeteerPage,
+} from '@/puppeteer/agent-launcher';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const { mockLaunch } = vi.hoisted(() => ({
+  mockLaunch: vi.fn(),
+}));
+
+const mockNewPage = vi.fn();
+const browserMock = {
+  newPage: mockNewPage,
+  setCookie: vi.fn(),
+  close: vi.fn(),
+};
+
+const createPageMock = () => ({
+  setUserAgent: vi.fn().mockResolvedValue(undefined),
+  setViewport: vi.fn().mockResolvedValue(undefined),
+  goto: vi.fn().mockResolvedValue(undefined),
+  waitForNetworkIdle: vi.fn().mockResolvedValue(undefined),
+});
+
+vi.mock('puppeteer', () => ({
+  __esModule: true,
+  default: { launch: mockLaunch },
+  launch: mockLaunch,
+}));
+
+describe('launchPuppeteerPage', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockLaunch.mockResolvedValue(browserMock);
+    const page = createPageMock();
+    mockNewPage.mockResolvedValue(page as any);
+  });
+
+  it('uses default viewport window size for headed runs', async () => {
+    await launchPuppeteerPage({ url: 'https://example.com' }, { headed: true });
+
+    const args = mockLaunch.mock.calls[0][0].args;
+    expect(args).toContain(
+      `--window-size=${defaultViewportWidth},${defaultViewportHeight + 200}`,
+    );
+    expect(args).not.toContain('--start-maximized');
+  });
+
+  it('respects provided viewport dimensions for headed runs', async () => {
+    await launchPuppeteerPage(
+      {
+        url: 'https://example.com',
+        viewportWidth: 1000,
+        viewportHeight: 700,
+      },
+      { headed: true },
+    );
+
+    const args = mockLaunch.mock.calls[0][0].args;
+    expect(args).toContain('--window-size=1000,900');
+    expect(args).not.toContain('--start-maximized');
+  });
+});