fix(browse): recreateContext() re-applies stealth (closes 4th un-stealth path)

useragent and viewport --scale route through recreateContext(), which rebuilds
the BrowserContext via newContext() — a fresh context with no init scripts. It
never called applyStealth, so a routine useragent/viewport-scale command
silently dropped webdriver masking, window.chrome.* shape, hardware spoof, and
the cdc/Permissions cleanup on every restored page. Caught by the cross-model
adversarial review (Codex) after the Claude pass and eng review missed it.

Both the main and fallback paths now call applyStealth before any page is
created. The launch-path tripwire is raised to >= 4 sites and now asserts the
recreateContext() body specifically, so the regression class can't recur.

Also documents the load-bearing trust assumption on buildGStackLaunchArgs /
readHostProfile (GSTACK_* must be gbd-sourced, never page/remote data — the
injection-safety argument depends on it) and the notifications-permission
spoof tradeoff.

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

browse/src/browser-manager.ts

@@ -1423,6 +1423,14 @@ export class BrowserManager {
       }
       this.context = await this.browser.newContext(contextOptions);
 
+      // Re-apply stealth: newContext() is a fresh context with no init scripts,
+      // so a useragent / viewport --scale rebuild would otherwise drop the
+      // webdriver mask, window.chrome.* shape, hardware spoof, and cdc/
+      // Permissions cleanup on every restored page. Must run before
+      // restoreState() navigates the restored tabs.
+      const { applyStealth } = await import('./stealth');
+      await applyStealth(this.context);
+
       if (Object.keys(this.extraHeaders).length > 0) {
         await this.context.setExtraHTTPHeaders(this.extraHeaders);
       }
@@ -1446,6 +1454,9 @@ export class BrowserManager {
           contextOptions.userAgent = this.customUserAgent;
         }
         this.context = await this.browser!.newContext(contextOptions);
+        // Stealth applies to the fallback blank context too.
+        const { applyStealth } = await import('./stealth');
+        await applyStealth(this.context);
         await this.newTab();
         this.clearRefs();
       } catch {

browse/src/stealth.ts

@@ -408,7 +408,11 @@ export const AUTOMATION_ARTIFACT_CLEANUP_SCRIPT = `(() => {
 
   // Permissions API: automated Chromium returns 'denied' for notifications,
   // a known tell. Return 'prompt' to match real Chrome (and Layer C's
-  // Notification.permission = 'default').
+  // Notification.permission = 'default'). Tradeoff: this pins the
+  // notifications state to fresh-Chrome values for the whole session, so a
+  // site that actually grants/denies notifications would see a stale value.
+  // Acceptable for the automation/anti-detection use case (which does not
+  // drive real notification grants); only notifications is overridden.
   const originalQuery = window.navigator.permissions && window.navigator.permissions.query;
   if (originalQuery) {
     window.navigator.permissions.query = (params) => {
@@ -422,8 +426,9 @@ export const AUTOMATION_ARTIFACT_CLEANUP_SCRIPT = `(() => {
 
 /**
  * Apply stealth patches to a fresh BrowserContext (or persistent context).
- * Called by browser-manager.launch(), launchHeaded(), AND handoff() so all
+ * Called by EVERY context-creation path in browser-manager — launch(),
- * three launch paths get identical stealth.
+ * launchHeaded(), handoff(), AND recreateContext() (the useragent /
+ * viewport --scale rebuild) — so a context can never reach a page un-stealthed.
  *
  * Injection order (Playwright evaluates init scripts in registration order):
  *   1. Layer C (buildStealthScript) — the always-on consistency-first default.
@@ -486,6 +491,14 @@ export const STEALTH_LAUNCH_ARGS = [
  * pre-Pack-1) and on hosts where gbd hasn't yet populated some
  * fields (legacy installs).
  *
+ * TRUSTED-SOURCE ONLY. These GSTACK_* values are populated by gbd from
+ * host_profile.go (system_profiler / sysctl) and become page-visible WebGL /
+ * UA-CH surface data. They are NOT sanitized here (passed verbatim into the
+ * argv array, which is injection-safe because Playwright spawns Chromium with
+ * an argv array, not a shell). NEVER route page content, HTTP headers, or any
+ * remote/untrusted input into these env vars — that would turn this into an
+ * argv-injection sink. readHostProfile() applies the same trust assumption.
+ *
  * Mapping (gbd env → Chromium cmdline switch → C++ patch consumer):
  *   GSTACK_GPU_VENDOR        → --gstack-gpu-vendor        → webgl-vendor-spoof.patch
  *   GSTACK_GPU_RENDERER      → --gstack-gpu-renderer      → webgl-vendor-spoof.patch

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

@@ -235,23 +235,36 @@ describe('BrowserManager.onDisconnect exit-code propagation', () => {
 // 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', () => {
+describe('stealth injected on every context-creation path', () => {
-  it('handoff() calls applyStealth and there are >= 3 call sites', async () => {
+  it('every context-creation path calls applyStealth (>= 4 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).
+    // Every path that builds a BrowserContext must apply stealth: launch()
+    // (headless), launchHeaded(), handoff(), and recreateContext() (the
+    // useragent / viewport --scale rebuild, main + fallback). A path that
+    // creates a context without applyStealth silently un-stealths its pages.
     const callSites = src.match(/applyStealth\(/g) || [];
-    expect(callSites.length).toBeGreaterThanOrEqual(3);
+    expect(callSites.length).toBeGreaterThanOrEqual(4);
 
-    // The handoff() method body specifically must call applyStealth, before
+    // handoff() body specifically must call applyStealth, before the resume() JSDoc.
-    // 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(');
+
+    // recreateContext() body must call applyStealth too — useragent and
+    // viewport --scale route through it and would otherwise drop all stealth.
+    const recreateStart = src.indexOf('recreateContext');
+    expect(recreateStart).toBeGreaterThan(0);
+    // Find the method definition (not just the JSDoc/caller references).
+    const recreateDef = src.indexOf('async recreateContext(');
+    expect(recreateDef).toBeGreaterThan(0);
+    const setUaAnchor = src.indexOf('async setDeviceScaleFactor(', recreateDef);
+    const recreateBody = src.slice(recreateDef, setUaAnchor > 0 ? setUaAnchor : recreateDef + 6000);
+    expect(recreateBody).toContain('applyStealth(');
   });
 
   it('buildGStackLaunchArgs() is spread into all 3 launch sites', async () => {