fix(browse): apply stealth on every launch path + share automation-artifact cleanup

handoff() built cmdline args but never called applyStealth, so a handed-off
browser had no JS stealth (no webdriver mask, no chrome.* shape, no toString
proxy). And the cdc_/Permissions cleanup shim lived inline in launchHeaded()
only, so headless launch() reported Notification.permission='default' without
the matching permissions.query='prompt' answer — the exact cross-source
inconsistency the shim exists to prevent.

Move the cleanup into AUTOMATION_ARTIFACT_CLEANUP_SCRIPT inside applyStealth so
all three launch paths (launch, launchHeaded, handoff) get identical stealth,
and call applyStealth(newContext) in handoff() before restoreState() navigates.

A static tripwire in browser-manager-unit.test.ts fails CI if any launch path
drops the applyStealth call again.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

browse/src/browser-manager.ts

@@ -592,48 +592,16 @@ export class BrowserManager {
     this.intentionalDisconnect = false;
 
     // ─── Anti-bot-detection patches ───────────────────────────────
-    // D7 (codex correction): mask navigator.webdriver only. We do NOT fake
-    // plugins/languages — modern fingerprinters check consistency between
-    // those and userAgent/platform, and synthesizing fixed values can flag
-    // MORE bot-like, not less. Let Chromium's natural plugins and languages
-    // surface unmodified.
-    //
-    // What we DO clean up are automation-specific runtime artifacts that
-    // shouldn't exist in a real browser at all (Permissions API quirks,
-    // ChromeDriver-injected window globals). Those aren't fingerprint
-    // synthesis — they're removing leaked automation tells.
+    // Apply Layer C stealth (applyStealth): masks navigator.webdriver,
+    // restores window.chrome.* shape, aligns Notification.permission, sets
+    // per-install hardware, and strips automation runtime artifacts (cdc_/
+    // __webdriver globals + the Permissions notifications 'denied' tell).
+    // We still do NOT fake navigator.plugins/languages — faking those flags
+    // more bot-like, not less (D7). The cdc/Permissions cleanup moved into
+    // applyStealth so headless launch() and handoff() get it too, not just
+    // this headed path.
     const { applyStealth } = await import('./stealth');
     await applyStealth(this.context);
-    await this.context.addInitScript(() => {
-      // Remove CDP runtime artifacts that automation detectors look for
-      // cdc_ prefixed vars are injected by ChromeDriver/CDP
-      const cleanup = () => {
-        for (const key of Object.keys(window)) {
-          if (key.startsWith('cdc_') || key.startsWith('__webdriver')) {
-            try {
-              delete (window as any)[key];
-            } catch (e: any) {
-              if (!(e instanceof TypeError)) throw e;
-            }
-          }
-        }
-      };
-      cleanup();
-      // Re-clean after a tick in case they're injected late
-      setTimeout(cleanup, 0);
-
-      // Override Permissions API to return 'prompt' for notifications
-      // (automation browsers return 'denied' which is a fingerprint)
-      const originalQuery = window.navigator.permissions?.query;
-      if (originalQuery) {
-        (window.navigator.permissions as any).query = (params: any) => {
-          if (params.name === 'notifications') {
-            return Promise.resolve({ state: 'prompt', onchange: null } as PermissionStatus);
-          }
-          return originalQuery.call(window.navigator.permissions, params);
-        };
-      }
-    });
 
     // Inject visual indicator — subtle top-edge amber gradient
     // Extension's content script handles the floating pill
@@ -1619,6 +1587,13 @@ export class BrowserManager {
       this.tabSessions.clear();
       this.connectionMode = 'headed';
 
+      // Same Layer C stealth as launch()/launchHeaded(). Must run BEFORE
+      // restoreState() navigates so the init scripts apply to the restored
+      // pages — without this the handed-off browser had cmdline args but no
+      // JS stealth (no webdriver mask, no chrome.* shape, no toString proxy).
+      const { applyStealth } = await import('./stealth');
+      await applyStealth(newContext);
+
       if (Object.keys(this.extraHeaders).length > 0) {
         await newContext.setExtraHTTPHeaders(this.extraHeaders);
       }

browse/src/stealth.ts

@@ -367,17 +367,69 @@ function extendedModeEnabled(): boolean {
 }
 
 /**
- * Apply stealth patches to a fresh BrowserContext (or persistent context).
- * Called by browser-manager.launch() and launchHeaded().
+ * Strip automation runtime artifacts that don't belong in a real browser
+ * and that no fingerprint-synthesis layer can mask: ChromeDriver/CDP window
+ * globals (cdc_*, __webdriver*) and the Permissions API quirk where an
+ * automated Chromium reports notifications as 'denied' instead of real
+ * Chrome's 'prompt'. The 'prompt' answer is aligned with Layer C's
+ * Notification.permission = 'default' so the two surfaces stay consistent.
  *
- * Always applies the always-on Layer C stealth script (built from the
- * per-install host profile) — the consistency-first default. When
- * GSTACK_STEALTH=extended is set, layers the opt-in EXTENDED_STEALTH_SCRIPT
- * on top: its window.chrome.* patches are `if (!...)`-guarded, so Layer C's
- * richer shapes win, while the extended-only additions (WebGL spoof, faked
- * navigator.plugins, mediaDevices, cdc_* cleanup) apply on top. Extended
- * mode actively LIES about the browser and can break sites that reflect on
- * these properties, so it stays off by default.
+ * Runs on EVERY launch path via applyStealth (headless launch(),
+ * launchHeaded(), handoff()) so the Notification/Permissions pairing never
+ * diverges by mode. Previously this lived inline in launchHeaded() only,
+ * which left headless and handoff with the Notification value but not the
+ * matching Permissions answer.
+ */
+const AUTOMATION_ARTIFACT_CLEANUP_SCRIPT = `(() => {
+  // cdc_/__webdriver globals are injected by ChromeDriver/CDP. A detector
+  // finds them by iterating window keys. Strip immediately and again after a
+  // tick in case they are injected late.
+  const cleanup = () => {
+    for (const key of Object.keys(window)) {
+      if (key.startsWith('cdc_') || key.startsWith('__webdriver')) {
+        try { delete window[key]; } catch (e) { if (!(e instanceof TypeError)) throw e; }
+      }
+    }
+  };
+  cleanup();
+  setTimeout(cleanup, 0);
+
+  // Permissions API: automated Chromium returns 'denied' for notifications,
+  // a known tell. Return 'prompt' to match real Chrome (and Layer C's
+  // Notification.permission = 'default').
+  const originalQuery = window.navigator.permissions && window.navigator.permissions.query;
+  if (originalQuery) {
+    window.navigator.permissions.query = (params) => {
+      if (params && params.name === 'notifications') {
+        return Promise.resolve({ state: 'prompt', onchange: null });
+      }
+      return originalQuery.call(window.navigator.permissions, params);
+    };
+  }
+})();`;
+
+/**
+ * Apply stealth patches to a fresh BrowserContext (or persistent context).
+ * Called by browser-manager.launch(), launchHeaded(), AND handoff() so all
+ * three launch paths get identical stealth.
+ *
+ * Injection order (Playwright evaluates init scripts in registration order):
+ *   1. Layer C (buildStealthScript) — the always-on consistency-first default.
+ *   2. Automation-artifact cleanup (cdc_/__webdriver + Permissions shim),
+ *      kept consistent with Layer C's Notification.permission alignment.
+ *   3. EXTENDED_STEALTH_SCRIPT — only when GSTACK_STEALTH=extended (off by
+ *      default). Its window.chrome.* patches are `if (!...)`-guarded, so
+ *      Layer C's richer shapes win; the extended-only additions (WebGL spoof,
+ *      faked navigator.plugins, mediaDevices) apply on top.
+ *
+ * KNOWN LIMITATION (extended mode only, opt-in): extended's functions are NOT
+ * wrapped by Layer C's Function.prototype.toString proxy, so they stringify
+ * as injected code; its prototype-level navigator.webdriver delete is shadowed
+ * by Layer C's own-property getter (net behavior still matches real Chrome:
+ * webdriver present and false); and its hardcoded Apple-M1 WebGL string can
+ * disagree with the env-driven GPU spoof in buildGStackLaunchArgs on non-Apple
+ * hosts. This is acceptable for the documented "actively lies, may break sites"
+ * escape hatch; the consistency-first default (Layer C alone) has none of these.
  *
  * Host profile is resolved from process.env at call time so per-install
  * values bake into the script before Playwright sends it to Chromium via
@@ -386,6 +438,7 @@ function extendedModeEnabled(): boolean {
 export async function applyStealth(context: BrowserContext): Promise<void> {
   const hw = readHostProfile();
   await context.addInitScript({ content: buildStealthScript(hw) });
+  await context.addInitScript({ content: AUTOMATION_ARTIFACT_CLEANUP_SCRIPT });
   if (extendedModeEnabled()) {
     await context.addInitScript({ content: EXTENDED_STEALTH_SCRIPT });
   }

browse/test/browser-manager-unit.test.ts

@@ -227,3 +227,30 @@ describe('BrowserManager.onDisconnect exit-code propagation', () => {
     expect(shutdownCalls).toEqual([0, 2, 2]);
   });
 });
+
+// ─── Stealth injected on EVERY launch path (regression tripwire) ───
+//
+// applyStealth must run on launch() (headless), launchHeaded(), AND
+// handoff(). The blend of Layer C with extended mode left handoff() building
+// cmdline args but never calling applyStealth, so a handed-off browser had
+// no JS stealth (no webdriver mask, no chrome.* shape, no toString proxy).
+// This static check fails CI if any launch path drops the call again.
+describe('stealth injected on every launch path', () => {
+  it('handoff() calls applyStealth and there are >= 3 call sites', async () => {
+    const { readFileSync } = await import('node:fs');
+    const { join } = await import('node:path');
+    const src = readFileSync(join(import.meta.dir, '..', 'src', 'browser-manager.ts'), 'utf-8');
+
+    // >= 3 total applyStealth call sites (launch, launchHeaded, handoff).
+    const callSites = src.match(/applyStealth\(/g) || [];
+    expect(callSites.length).toBeGreaterThanOrEqual(3);
+
+    // The handoff() method body specifically must call applyStealth, before
+    // the resume() JSDoc that follows it.
+    const handoffStart = src.indexOf('async handoff(');
+    expect(handoffStart).toBeGreaterThan(0);
+    const resumeAnchor = src.indexOf('Resume AI control after user handoff', handoffStart);
+    const handoffBody = src.slice(handoffStart, resumeAnchor > 0 ? resumeAnchor : handoffStart + 4000);
+    expect(handoffBody).toContain('applyStealth(');
+  });
+});

browse/test/stealth-extended.test.ts

@@ -89,7 +89,7 @@ describe('EXTENDED_STEALTH_SCRIPT — six detection-vector patches', () => {
 });
 
 describe('applyStealth — script wiring', () => {
-  test('default mode applies ONLY the Layer C script (not extended)', async () => {
+  test('default mode applies Layer C + cleanup, not extended', async () => {
     delete process.env.GSTACK_STEALTH;
     const calls: string[] = [];
     const fakeCtx = {
@@ -98,14 +98,19 @@ describe('applyStealth — script wiring', () => {
       },
     } as unknown as Parameters<typeof applyStealth>[0];
     await applyStealth(fakeCtx);
-    expect(calls).toHaveLength(1);
-    // Layer C signatures: toString-proxy native-code lie + webdriver mask.
+    expect(calls).toHaveLength(2);
+    // [0] = Layer C (toString-proxy native-code lie + webdriver mask).
     expect(calls[0]).toContain('[native code]');
     expect(calls[0]).toContain('webdriver');
-    expect(calls[0]).not.toBe(EXTENDED_STEALTH_SCRIPT);
+    // [1] = automation-artifact cleanup (cdc_ scan + Permissions shim) —
+    //       now applied on EVERY launch path, not just the headed one.
+    expect(calls[1]).toContain('cdc_');
+    expect(calls[1]).toContain('setTimeout(cleanup');
+    // Extended script must NOT be applied by default.
+    expect(calls).not.toContain(EXTENDED_STEALTH_SCRIPT);
   });
 
-  test('extended mode applies BOTH scripts in order (Layer C first, extended second)', async () => {
+  test('extended mode applies Layer C, cleanup, then extended (in order)', async () => {
     process.env.GSTACK_STEALTH = 'extended';
     const calls: string[] = [];
     const fakeCtx = {
@@ -114,9 +119,9 @@ describe('applyStealth — script wiring', () => {
       },
     } as unknown as Parameters<typeof applyStealth>[0];
     await applyStealth(fakeCtx);
-    expect(calls).toHaveLength(2);
-    // Layer C first (its native-code lie), extended second.
-    expect(calls[0]).toContain('[native code]');
-    expect(calls[1]).toBe(EXTENDED_STEALTH_SCRIPT);
+    expect(calls).toHaveLength(3);
+    expect(calls[0]).toContain('[native code]');     // Layer C first
+    expect(calls[1]).toContain('cdc_');              // cleanup second
+    expect(calls[2]).toBe(EXTENDED_STEALTH_SCRIPT);  // extended last
   });
 });