diff --git a/browse/src/browser-manager.ts b/browse/src/browser-manager.ts
index 4dc9cf857..ffc8b5d7e 100644
--- a/browse/src/browser-manager.ts
+++ b/browse/src/browser-manager.ts
@@ -73,6 +73,82 @@ export function shouldEnableChromiumSandbox(): boolean {
   return !(process.env.CI || process.env.CONTAINER || isRoot);
 }
 
+/**
+ * Thrown by probePoisonedChromiumBundle() when it finds — and removes — a
+ * Chromium bundle poisoned by the pre-v1.64 in-place rebrand (#2242).
+ * Call sites rethrow on `instanceof` (never message-string sniffing) so the
+ * actionable remediation reaches the user instead of being swallowed by the
+ * probe's fall-through-on-failure catch.
+ */
+export class PoisonedBundleError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = 'PoisonedBundleError';
+  }
+}
+
+/**
+ * Self-heal probe for bundles the OLD (pre-v1.64) rebrand code already
+ * poisoned (#2242): the mutation lives in the SHARED Playwright cache, so
+ * deleting the rebrand code fixes fresh installs only, and the documented
+ * deploy paths never run upgrade migrations. Detect the mutated plist and
+ * remove the bundle so the next `playwright install chromium` (or the
+ * upgrade migration) re-fetches a clean one.
+ *
+ * Removal scope: when the .app sits in the standard Playwright cache layout
+ * (chromium-<rev>/chrome-mac/<name>.app), the WHOLE chromium-<rev> revision
+ * dir is removed — Playwright's INSTALLATION_COMPLETE marker lives there,
+ * and `playwright install chromium` treats its presence as "is already
+ * downloaded", so removing only the .app would turn our own remediation
+ * command into a no-op that leaves the user with no browser at all. Outside
+ * that layout, the .app plus any sibling INSTALLATION_COMPLETE /
+ * DEPENDENCIES_VALIDATED markers are removed.
+ *
+ * Caller contract: pass ONLY Playwright-cache executables
+ * (chromium.executablePath()). A bundle supplied via GSTACK_CHROMIUM_PATH
+ * belongs to the wrapper/embedder — its plist legitimately says "GStack
+ * Browser" — and must never be deleted. Both call sites (launchHeaded and
+ * handoff) honor this, and as a second belt the probe refuses to act on the
+ * GSTACK_CHROMIUM_PATH executable itself.
+ *
+ * @param chromiumExecutablePath the Chromium binary inside the .app
+ *   (…/<name>.app/Contents/MacOS/<name>), as returned by
+ *   chromium.executablePath().
+ * @throws PoisonedBundleError after removing a poisoned bundle — the
+ *   message carries the re-fetch command for the user.
+ */
+export function probePoisonedChromiumBundle(chromiumExecutablePath: string): void {
+  const fs = require('fs');
+  const path = require('path');
+
+  // Belt to the caller contract: never act on the custom/embedder bundle.
+  const customPath = process.env.GSTACK_CHROMIUM_PATH;
+  if (customPath && path.resolve(chromiumExecutablePath) === path.resolve(customPath)) {
+    return;
+  }
+
+  const chromeContentsDir = path.resolve(path.dirname(chromiumExecutablePath), '..');
+  const chromePlist = path.join(chromeContentsDir, 'Info.plist');
+  if (!fs.existsSync(chromePlist)) return;
+  if (!fs.readFileSync(chromePlist, 'utf-8').includes('GStack Browser')) return;
+
+  const appDir = path.resolve(chromeContentsDir, '..');
+  const revisionDir = path.resolve(appDir, '..', '..');
+  if (/^chromium-\d+$/.test(path.basename(revisionDir))) {
+    fs.rmSync(revisionDir, { recursive: true, force: true });
+  } else {
+    fs.rmSync(appDir, { recursive: true, force: true });
+    for (const marker of ['INSTALLATION_COMPLETE', 'DEPENDENCIES_VALIDATED']) {
+      fs.rmSync(path.join(path.dirname(appDir), marker), { force: true });
+    }
+  }
+  throw new PoisonedBundleError(
+    'Chromium bundle was mutated by a previous gstack version (broken codesign seal — ' +
+    'GPU exit_code=5 on macOS 26). The poisoned bundle has been removed. ' +
+    'Re-fetch a clean one with: bunx playwright install chromium — then retry.',
+  );
+}
+
 /**
  * Resolve why the underlying Chromium ChildProcess is going away.
  *
@@ -521,30 +597,17 @@ export class BrowserManager {
     // bundle here — browse/test/rebrand-signed-bundle.test.ts fails CI if
     // you do.
     //
-    // Self-heal for bundles the OLD code already poisoned: the mutation
-    // lives in the SHARED Playwright cache, so deleting the rebrand code
-    // fixes fresh installs only, and the documented deploy paths never run
-    // upgrade migrations. Detect the mutated plist and remove the bundle so
-    // the next `playwright install chromium` (or the upgrade migration)
-    // re-fetches a clean one. Scoped to the Playwright cache copy — a
+    // Self-heal for bundles the OLD code already poisoned: probe the
+    // Playwright-cache bundle and remove it when the mutated plist is
+    // present (see probePoisonedChromiumBundle for the removal-scope
+    // rationale). Scoped to the Playwright cache copy — a
     // GSTACK_CHROMIUM_PATH bundle belongs to the wrapper/embedder and is
-    // never touched.
+    // never probed.
     if (!executablePath) {
       try {
-        const chromePath = chromium.executablePath();
-        const chromeContentsDir = path.resolve(path.dirname(chromePath), '..');
-        const chromePlist = path.join(chromeContentsDir, 'Info.plist');
-        if (fs.existsSync(chromePlist) && fs.readFileSync(chromePlist, 'utf-8').includes('GStack Browser')) {
-          const appDir = path.resolve(chromeContentsDir, '..');
-          fs.rmSync(appDir, { recursive: true, force: true });
-          throw new Error(
-            'Chromium bundle was mutated by a previous gstack version (broken codesign seal — ' +
-            'GPU exit_code=5 on macOS 26). The poisoned bundle has been removed. ' +
-            'Re-fetch a clean one with: bunx playwright install chromium — then retry.',
-          );
-        }
-      } catch (err: any) {
-        if (err?.message?.includes('poisoned bundle')) throw err;
+        probePoisonedChromiumBundle(chromium.executablePath());
+      } catch (err: unknown) {
+        if (err instanceof PoisonedBundleError) throw err;
         // Probe failures (no bundle yet, EACCES) fall through to launch,
         // which produces its own actionable error.
       }
@@ -1579,6 +1642,20 @@ export class BrowserManager {
       const userDataDir = path.join(process.env.HOME || '/tmp', '.gstack', 'chromium-profile');
       fs.mkdirSync(userDataDir, { recursive: true });
 
+      // Self-heal probe (#2242): handoff always launches the Playwright-cache
+      // bundle (this launchPersistentContext call passes no executablePath),
+      // so a bundle poisoned by the old in-place rebrand would GPU-crash here
+      // exactly like launchHeaded(). Same probe, same contract: a
+      // GSTACK_CHROMIUM_PATH bundle is never passed in. The rethrown typed
+      // error surfaces through the outer catch as the actionable
+      // "Cannot open headed browser" message, headless browser untouched.
+      try {
+        probePoisonedChromiumBundle(chromium.executablePath());
+      } catch (err: unknown) {
+        if (err instanceof PoisonedBundleError) throw err;
+        // Probe failures (no bundle yet, EACCES) fall through to launch.
+      }
+
       // T1: same automation-tell-stripping defaults as launchHeaded().
       // The handoff path (headless → headed re-launch) takes the same
       // anti-detection posture.
diff --git a/browse/test/poisoned-bundle-probe.test.ts b/browse/test/poisoned-bundle-probe.test.ts
new file mode 100644
index 000000000..0ae4a8a5f
--- /dev/null
+++ b/browse/test/poisoned-bundle-probe.test.ts
@@ -0,0 +1,148 @@
+/**
+ * Unit tests for the extracted poisoned-bundle self-heal probe (#2242).
+ *
+ * probePoisonedChromiumBundle() detects a Chromium bundle mutated by the
+ * pre-v1.64 in-place rebrand (Info.plist contains "GStack Browser"),
+ * removes it so `playwright install chromium` actually re-downloads, and
+ * throws a typed PoisonedBundleError with the remediation command.
+ *
+ * Contracts pinned here:
+ *   - standard cache layout (chromium-<rev>/chrome-mac/<name>.app): the
+ *     WHOLE revision dir is removed, INSTALLATION_COMPLETE marker included
+ *     (leaving the marker makes the recommended re-fetch a no-op)
+ *   - non-cache layout: the .app + sibling install markers are removed,
+ *     nothing else
+ *   - clean bundle: untouched, no throw
+ *   - GSTACK_CHROMIUM_PATH bundles (custom/embedder) are NEVER deleted:
+ *     the probe refuses to act on that executable, and both call sites
+ *     (launchHeaded + handoff) only pass chromium.executablePath()
+ *   - the rethrow guard at the call sites is typed (instanceof), not a
+ *     fragile message-string match
+ */
+
+import { describe, test, expect, beforeEach, afterEach } from 'bun:test';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import { probePoisonedChromiumBundle, PoisonedBundleError } from '../src/browser-manager';
+
+const SRC = fs.readFileSync(
+  path.join(import.meta.dir, '..', 'src', 'browser-manager.ts'),
+  'utf-8',
+);
+
+const POISONED_PLIST =
+  '<plist><dict><key>CFBundleName</key><string>GStack Browser</string></dict></plist>';
+const CLEAN_PLIST =
+  '<plist><dict><key>CFBundleName</key><string>Google Chrome for Testing</string></dict></plist>';
+
+let tmpDir: string;
+let savedCustomPath: string | undefined;
+
+/** Build <parentDir>/<name>.app with a plist and executable; return the executable path. */
+function makeApp(parentDir: string, plist: string): { appDir: string; exe: string } {
+  const appDir = path.join(parentDir, 'Google Chrome for Testing.app');
+  const macos = path.join(appDir, 'Contents', 'MacOS');
+  fs.mkdirSync(macos, { recursive: true });
+  fs.writeFileSync(path.join(appDir, 'Contents', 'Info.plist'), plist);
+  const exe = path.join(macos, 'Google Chrome for Testing');
+  fs.writeFileSync(exe, '#!/bin/sh\n', { mode: 0o755 });
+  return { appDir, exe };
+}
+
+beforeEach(() => {
+  tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'poison-probe-'));
+  savedCustomPath = process.env.GSTACK_CHROMIUM_PATH;
+  delete process.env.GSTACK_CHROMIUM_PATH;
+});
+
+afterEach(() => {
+  fs.rmSync(tmpDir, { recursive: true, force: true });
+  if (savedCustomPath === undefined) delete process.env.GSTACK_CHROMIUM_PATH;
+  else process.env.GSTACK_CHROMIUM_PATH = savedCustomPath;
+});
+
+describe('probePoisonedChromiumBundle — poisoned cache bundle', () => {
+  test('standard cache layout: whole chromium-<rev> dir removed (markers included), typed error thrown', () => {
+    const revDir = path.join(tmpDir, 'ms-playwright', 'chromium-1234');
+    const { exe } = makeApp(path.join(revDir, 'chrome-mac'), POISONED_PLIST);
+    fs.writeFileSync(path.join(revDir, 'INSTALLATION_COMPLETE'), '');
+    fs.writeFileSync(path.join(revDir, 'DEPENDENCIES_VALIDATED'), '');
+
+    let caught: unknown;
+    try {
+      probePoisonedChromiumBundle(exe);
+    } catch (err) {
+      caught = err;
+    }
+    expect(caught).toBeInstanceOf(PoisonedBundleError);
+    // The message is the user's remediation — it must carry the command.
+    expect((caught as Error).message).toContain('playwright install chromium');
+    // Whole revision dir gone: leaving INSTALLATION_COMPLETE behind makes
+    // `playwright install chromium` no-op ("is already downloaded") and the
+    // remediation we just printed would do nothing.
+    expect(fs.existsSync(revDir)).toBe(false);
+  });
+
+  test('non-cache layout: only the .app + sibling install markers removed, neighbors survive', () => {
+    const parentDir = path.join(tmpDir, 'custom-bundles');
+    const { appDir, exe } = makeApp(parentDir, POISONED_PLIST);
+    fs.writeFileSync(path.join(parentDir, 'INSTALLATION_COMPLETE'), '');
+    fs.writeFileSync(path.join(parentDir, 'DEPENDENCIES_VALIDATED'), '');
+    fs.writeFileSync(path.join(parentDir, 'unrelated.txt'), 'keep me');
+
+    expect(() => probePoisonedChromiumBundle(exe)).toThrow(PoisonedBundleError);
+    expect(fs.existsSync(appDir)).toBe(false);
+    expect(fs.existsSync(path.join(parentDir, 'INSTALLATION_COMPLETE'))).toBe(false);
+    expect(fs.existsSync(path.join(parentDir, 'DEPENDENCIES_VALIDATED'))).toBe(false);
+    // The parent dir itself and unrelated files are NOT swept.
+    expect(fs.readFileSync(path.join(parentDir, 'unrelated.txt'), 'utf-8')).toBe('keep me');
+  });
+});
+
+describe('probePoisonedChromiumBundle — clean and missing bundles', () => {
+  test('clean plist: untouched, no throw', () => {
+    const revDir = path.join(tmpDir, 'ms-playwright', 'chromium-1234');
+    const { appDir, exe } = makeApp(path.join(revDir, 'chrome-mac'), CLEAN_PLIST);
+    fs.writeFileSync(path.join(revDir, 'INSTALLATION_COMPLETE'), '');
+
+    expect(() => probePoisonedChromiumBundle(exe)).not.toThrow();
+    expect(fs.existsSync(path.join(appDir, 'Contents', 'Info.plist'))).toBe(true);
+    expect(fs.existsSync(path.join(revDir, 'INSTALLATION_COMPLETE'))).toBe(true);
+  });
+
+  test('no plist at the probed path: no-op, no throw (bundle not installed yet)', () => {
+    expect(() =>
+      probePoisonedChromiumBundle(path.join(tmpDir, 'nope.app', 'Contents', 'MacOS', 'nope')),
+    ).not.toThrow();
+  });
+});
+
+describe('probePoisonedChromiumBundle — GSTACK_CHROMIUM_PATH is never deleted', () => {
+  test('probe refuses to act on the GSTACK_CHROMIUM_PATH executable, even when poisoned', () => {
+    // A custom/embedder bundle (GStack Browser.app wrapper) legitimately
+    // contains "GStack Browser" in its plist — that is its branding, not
+    // cache poison. Deleting it would destroy the embedder's product.
+    const { appDir, exe } = makeApp(path.join(tmpDir, 'GStack Browser.app-parent'), POISONED_PLIST);
+    process.env.GSTACK_CHROMIUM_PATH = exe;
+
+    expect(() => probePoisonedChromiumBundle(exe)).not.toThrow();
+    expect(fs.existsSync(path.join(appDir, 'Contents', 'Info.plist'))).toBe(true);
+    expect(fs.existsSync(exe)).toBe(true);
+  });
+
+  test('caller contract: both headed launch paths probe chromium.executablePath() only', () => {
+    // launchHeaded + handoff each call the probe with the Playwright-cache
+    // path. No call site may ever pass the custom-bundle env var.
+    const calls = SRC.match(/probePoisonedChromiumBundle\(chromium\.executablePath\(\)\)/g) || [];
+    expect(calls.length).toBeGreaterThanOrEqual(2);
+    expect(SRC).not.toMatch(/probePoisonedChromiumBundle\([^)]*GSTACK_CHROMIUM_PATH/);
+  });
+});
+
+describe('typed rethrow guard at the call sites', () => {
+  test('instanceof PoisonedBundleError, not message-string sniffing', () => {
+    expect(SRC).not.toContain("includes('poisoned bundle')");
+    expect(SRC).toMatch(/instanceof PoisonedBundleError/);
+  });
+});