diff --git a/integrations/test-failure-explorer/src/report-store.test.ts b/integrations/test-failure-explorer/src/report-store.test.ts
index f8eb57eb454..657c5644309 100644
--- a/integrations/test-failure-explorer/src/report-store.test.ts
+++ b/integrations/test-failure-explorer/src/report-store.test.ts
@@ -20,6 +20,7 @@ import { afterEach, describe, expect, it, vi } from 'vitest';
 import { MAX_SNAPSHOT_BYTES, MAX_SOURCE_BYTES } from './contracts.js';
 import { ReportStore } from './report-store.js';
 import { parseVitestReport } from './vitest-report.js';
+import { arePermissionBitsEnforced } from './test-utils/permission-bits.js';
 
 const roots: string[] = [];
 async function workspace(): Promise<string> {
@@ -319,7 +320,7 @@ describe('workspace report snapshots', () => {
     expect(await readFile(path, 'utf8')).toBe(altered);
   });
 
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'reports an actually unwritable cache without claiming an import',
     async () => {
       const root = await workspace();
diff --git a/integrations/test-failure-explorer/src/test-utils/permission-bits.ts b/integrations/test-failure-explorer/src/test-utils/permission-bits.ts
new file mode 100644
index 00000000000..adfa456fea6
--- /dev/null
+++ b/integrations/test-failure-explorer/src/test-utils/permission-bits.ts
@@ -0,0 +1,135 @@
+/**
+ * @license
+ * Copyright 2026 Qwen Team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { createRequire } from 'node:module';
+import * as path from 'node:path';
+import { expect } from 'vitest';
+
+/** The node:fs calls the probe makes. */
+export interface ProbeFs {
+  mkdtempSync(prefix: string): string;
+  chmodSync(path: string, mode: number): void;
+  readdirSync(path: string): unknown;
+  writeFileSync(path: string, data: string): void;
+  rmSync(path: string, options: { recursive: boolean; force: boolean }): void;
+}
+
+// The real node:fs and node:os, even when the test file that asks has
+// vi.mock()ed them: vitest mocks its own module graph, not a builtin loaded
+// through Node's require. A mocked fs would answer for the mock, not the
+// kernel. A vi.spyOn on node:fs's default export at collection time would
+// still reach the probe, since that export is this same module object.
+const nodeRequire = createRequire(import.meta.url);
+const realFs = nodeRequire('node:fs') as typeof import('node:fs');
+const realOs = nodeRequire('node:os') as typeof import('node:os');
+
+/**
+ * Whether file permission bits bind this process, for tests that force a
+ * failure with `chmod`. They do not on Windows, which ignores Unix-style
+ * bits, nor for root, which bypasses them (on Linux through
+ * CAP_DAC_OVERRIDE and CAP_DAC_READ_SEARCH). ci.yml drops both
+ * capabilities when it runs unit tests as root (package-scripts.test.js
+ * pins that), so asking the kernel, rather than checking for uid 0, keeps
+ * those tests running there. A probe that cannot measure also answers
+ * false, and says so on stderr.
+ * `fs` is for this helper's own tests; every caller probes the real one.
+ */
+export function arePermissionBitsEnforced(fs: ProbeFs = realFs): boolean {
+  if (process.platform === 'win32') return false;
+  let dir: string | undefined;
+  try {
+    dir = fs.mkdtempSync(path.join(realOs.tmpdir(), 'qwen-permission-probe-'));
+    fs.chmodSync(dir, 0o000);
+    const probe = dir;
+    return (
+      refused(() => fs.readdirSync(probe)) &&
+      refused(() => fs.writeFileSync(path.join(probe, 'probe'), ''))
+    );
+  } catch (error) {
+    // A temp directory that cannot hold the probe, or refuses chmod,
+    // cannot hold these tests' fixtures either, though after a transient
+    // ENOSPC it may hold them again by the time they run, so say which it
+    // was rather than skip silently.
+    inconclusive(error);
+    return false;
+  } finally {
+    if (dir !== undefined) {
+      try {
+        fs.chmodSync(dir, 0o700);
+      } catch {
+        // Best effort, like the removal below: newer Node versions refuse
+        // to remove even an empty mode-000 directory.
+      }
+      try {
+        fs.rmSync(dir, { recursive: true, force: true });
+      } catch {
+        // Best effort: a leftover probe must not fail the test file.
+      }
+    }
+  }
+}
+
+function refused(attempt: () => unknown): boolean {
+  try {
+    attempt();
+    return false;
+  } catch (error) {
+    if (errnoOf(error) === 'EACCES') return true;
+    inconclusive(error);
+    return false;
+  }
+}
+
+function errnoOf(error: unknown): string | undefined {
+  const code = attempt(
+    () => (error as NodeJS.ErrnoException | null | undefined)?.code,
+  );
+  return typeof code === 'string' ? code : undefined;
+}
+
+/**
+ * Names a probe that could not measure, and the test file that asked, so
+ * the skips it causes are not mistaken for a Windows or root run. vitest's
+ * `silent: true` drops console output, so this writes to stderr directly.
+ * Under GitHub Actions the line opens with a workflow command, so the skips
+ * show in the check UI and not only deep in the log.
+ */
+function inconclusive(error: unknown): void {
+  try {
+    process.stderr.write(
+      `${process.env['GITHUB_ACTIONS'] === 'true' ? '::warning::' : ''}` +
+        `[permission-bits] probe inconclusive (${causeOf(error)})${askedBy()}; ` +
+        'treating permission bits as unenforced, so chmod-based tests skip\n',
+    );
+  } catch {
+    // A diagnostic must never fail the test file it is meant to explain.
+  }
+}
+
+function causeOf(error: unknown): string {
+  const code = errnoOf(error);
+  if (code === undefined) {
+    return (
+      attempt(() => String(error).split('\n', 1)[0]) ?? 'an unprintable value'
+    );
+  }
+  const syscall = attempt(() => (error as NodeJS.ErrnoException).syscall);
+  return typeof syscall === 'string' ? `${code} in ${syscall}` : code;
+}
+
+function askedBy(): string {
+  const testPath = attempt(() => expect.getState().testPath);
+  if (!testPath) return '';
+  return ` for ${attempt(() => path.relative(process.cwd(), testPath)) ?? testPath}`;
+}
+
+function attempt<T>(read: () => T): T | undefined {
+  try {
+    return read();
+  } catch {
+    return undefined;
+  }
+}
diff --git a/packages/browser-use/src/native-host-installer.test.ts b/packages/browser-use/src/native-host-installer.test.ts
index 1efb05dfa2a..aa2ff5e6e5a 100644
--- a/packages/browser-use/src/native-host-installer.test.ts
+++ b/packages/browser-use/src/native-host-installer.test.ts
@@ -26,6 +26,7 @@ import {
   CHROME_NATIVE_HOST_NAME,
   CHROME_NATIVE_HOST_REVISION,
 } from './bridge/protocol.js';
+import { arePermissionBitsEnforced } from './test-utils/permission-bits.js';
 
 const roots: string[] = [];
 
@@ -178,9 +179,7 @@ describe('Chrome Native Host installer', () => {
     );
   });
 
-  it
-    .skipIf(process.platform === 'win32' || process.getuid?.() === 0)
-    .each(['launcher', 'manifest'])(
+  it.skipIf(!arePermissionBitsEnforced()).each(['launcher', 'manifest'])(
     'preserves an unreadable %s during install, status and uninstall',
     async (kind) => {
       const fixture = createFixture();
@@ -265,7 +264,7 @@ describe('Chrome Native Host installer', () => {
   });
 
   it
-    .skipIf(process.platform === 'win32' || process.getuid?.() === 0)
+    .skipIf(!arePermissionBitsEnforced())
     .each(['launcher', 'manifest'] as const)(
     'keeps a correct %s usable in a read-only directory',
     async (kind) => {
@@ -313,7 +312,7 @@ describe('Chrome Native Host installer', () => {
     },
   );
 
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'propagates a required launcher update failure and updates when writable',
     async () => {
       const fixture = createFixture();
diff --git a/packages/browser-use/src/runtime.test.ts b/packages/browser-use/src/runtime.test.ts
index 8d290209cbd..70f42a93dc6 100644
--- a/packages/browser-use/src/runtime.test.ts
+++ b/packages/browser-use/src/runtime.test.ts
@@ -8,6 +8,7 @@ import fs from 'node:fs';
 import os from 'node:os';
 import path from 'node:path';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { arePermissionBitsEnforced } from './test-utils/permission-bits.js';
 
 const installer = vi.hoisted(() => ({
   ensure: vi.fn(async () => ({
@@ -93,7 +94,7 @@ describe('createBrowserBackend', () => {
     });
   });
 
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'initializes when Chrome preference files are unreadable',
     async () => {
       vi.spyOn(process, 'platform', 'get').mockReturnValue('darwin');
diff --git a/packages/browser-use/src/test-utils/permission-bits.mocked-fs.test.ts b/packages/browser-use/src/test-utils/permission-bits.mocked-fs.test.ts
new file mode 100644
index 00000000000..2c205c55ce8
--- /dev/null
+++ b/packages/browser-use/src/test-utils/permission-bits.mocked-fs.test.ts
@@ -0,0 +1,81 @@
+/**
+ * @license
+ * Copyright 2026 Qwen Team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import mockedFsDefault, * as mockedFs from 'node:fs';
+import { createRequire } from 'node:module';
+import * as os from 'node:os';
+import * as path from 'node:path';
+import { expect, it, vi } from 'vitest';
+
+import { arePermissionBitsEnforced } from './permission-bits.js';
+
+// A test file that replaces node:fs, as some callers of the probe do, must
+// not change its answer: the probe asks the kernel, not the mock. The test
+// makes the mock answer the opposite of the kernel, so a probe that read the
+// mock fails here whoever runs it.
+const mocked = vi.hoisted(() => ({
+  mkdtempSync: vi.fn(),
+  readdirSync: vi.fn(),
+  writeFileSync: vi.fn(),
+}));
+// Both the named exports and the default one: a probe reading either would
+// answer for the mock.
+vi.mock('node:fs', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('node:fs')>();
+  return { ...actual, ...mocked, default: { ...actual, ...mocked } };
+});
+
+const realFs = createRequire(import.meta.url)(
+  'node:fs',
+) as typeof import('node:fs');
+
+function refusedWithEacces(attempt: () => unknown): boolean {
+  try {
+    attempt();
+    return false;
+  } catch (error) {
+    return (error as NodeJS.ErrnoException).code === 'EACCES';
+  }
+}
+
+it.skipIf(process.platform === 'win32')(
+  'answers for the kernel while the test file mocks node:fs',
+  () => {
+    // The mock is in place, both ways, or this test would pass without
+    // pinning anything. Asked of the graph's node:fs, never of realFs,
+    // which the mock never reaches.
+    expect(mockedFs.mkdtempSync).toBe(mocked.mkdtempSync);
+    expect(mockedFsDefault.mkdtempSync).toBe(mocked.mkdtempSync);
+    const dir = realFs.mkdtempSync(path.join(os.tmpdir(), 'locked-'));
+    realFs.chmodSync(dir, 0o000);
+    let enforced: boolean;
+    try {
+      enforced =
+        refusedWithEacces(() => realFs.readdirSync(dir)) &&
+        refusedWithEacces(() =>
+          realFs.writeFileSync(path.join(dir, 'probe'), ''),
+        );
+    } finally {
+      realFs.chmodSync(dir, 0o700);
+      realFs.rmSync(dir, { recursive: true, force: true });
+    }
+    mocked.mkdtempSync.mockImplementation((prefix: string) =>
+      realFs.mkdtempSync(prefix),
+    );
+    if (enforced) {
+      // The mock lists and writes freely: it would answer false.
+      mocked.readdirSync.mockReturnValue([]);
+    } else {
+      // The mock refuses both: it would answer true.
+      const eacces = () => {
+        throw Object.assign(new Error('EACCES'), { code: 'EACCES' });
+      };
+      mocked.readdirSync.mockImplementation(eacces);
+      mocked.writeFileSync.mockImplementation(eacces);
+    }
+    expect(arePermissionBitsEnforced()).toBe(enforced);
+  },
+);
diff --git a/packages/browser-use/src/test-utils/permission-bits.test.ts b/packages/browser-use/src/test-utils/permission-bits.test.ts
new file mode 100644
index 00000000000..4ab10cb12c7
--- /dev/null
+++ b/packages/browser-use/src/test-utils/permission-bits.test.ts
@@ -0,0 +1,310 @@
+/**
+ * @license
+ * Copyright 2026 Qwen Team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import * as path from 'node:path';
+import {
+  afterEach,
+  beforeEach,
+  describe,
+  expect,
+  it,
+  vi,
+  type MockInstance,
+} from 'vitest';
+
+import { arePermissionBitsEnforced } from './permission-bits.js';
+
+/** The real filesystem, with each call the probe makes open to a fault. */
+function probeFs() {
+  return {
+    mkdtempSync: vi.fn((prefix: string) => fs.mkdtempSync(prefix)),
+    chmodSync: vi.fn((file: string, mode: number) => fs.chmodSync(file, mode)),
+    readdirSync: vi.fn((file: string): unknown => fs.readdirSync(file)),
+    writeFileSync: vi.fn((file: string, data: string) =>
+      fs.writeFileSync(file, data),
+    ),
+    rmSync: vi.fn(
+      (file: string, options: { recursive: boolean; force: boolean }) =>
+        fs.rmSync(file, options),
+    ),
+  };
+}
+
+function refusal(code: string, syscall?: string): () => never {
+  return () => {
+    throw Object.assign(new Error(code), { code, syscall });
+  };
+}
+
+describe('arePermissionBitsEnforced', () => {
+  const initialTmpdir = process.env['TMPDIR'];
+  let tmp: string;
+  let stderr: MockInstance<typeof process.stderr.write>;
+  let probe: ReturnType<typeof probeFs>;
+
+  beforeEach(() => {
+    tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'permission-bits-test-'));
+    process.env['TMPDIR'] = tmp;
+    // The diagnostic's shape depends on it, and CI sets it.
+    vi.stubEnv('GITHUB_ACTIONS', '');
+    stderr = vi.spyOn(process.stderr, 'write').mockImplementation(() => true);
+    probe = probeFs();
+  });
+
+  afterEach(() => {
+    stderr.mockRestore();
+    vi.unstubAllEnvs();
+    if (initialTmpdir === undefined) delete process.env['TMPDIR'];
+    else process.env['TMPDIR'] = initialTmpdir;
+    fs.rmSync(tmp, { recursive: true, force: true });
+  });
+
+  /** What the probe wrote to stderr about an inconclusive measurement. */
+  function diagnostics(): string[] {
+    return stderr.mock.calls
+      .map((call) => String(call[0]))
+      .filter((line) => /^(::warning::)?\[permission-bits\]/.test(line));
+  }
+
+  /** The probe was made in os.tmpdir() and is gone again. */
+  function expectProbeCleanedUp(): void {
+    const dir = String(probe.chmodSync.mock.calls[0]?.[0]);
+    expect(dir.startsWith(path.join(tmp, 'qwen-permission-probe-'))).toBe(true);
+    expect(fs.readdirSync(tmp)).toEqual([]);
+  }
+
+  it.skipIf(process.platform === 'win32')(
+    'answers true only when listing and writing are both refused',
+    () => {
+      probe.readdirSync.mockImplementationOnce(refusal('EACCES'));
+      probe.writeFileSync.mockImplementationOnce(refusal('EACCES'));
+      expect(arePermissionBitsEnforced(probe)).toBe(true);
+      expectProbeCleanedUp();
+      expect(diagnostics()).toEqual([]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'answers false when the directory can still be listed',
+    () => {
+      probe.readdirSync.mockImplementationOnce(() => []);
+      probe.writeFileSync.mockImplementationOnce(refusal('EACCES'));
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expectProbeCleanedUp();
+      // Bits that do not bind are an answer, not a failed measurement.
+      expect(diagnostics()).toEqual([]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'answers false when listing is refused but writing is not',
+    () => {
+      probe.readdirSync.mockImplementationOnce(refusal('EACCES'));
+      probe.writeFileSync.mockImplementationOnce(() => undefined);
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expectProbeCleanedUp();
+      expect(diagnostics()).toEqual([]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'answers false for a refusal other than EACCES',
+    () => {
+      probe.readdirSync.mockImplementationOnce(refusal('EPERM'));
+      probe.writeFileSync.mockImplementationOnce(refusal('EACCES'));
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expectProbeCleanedUp();
+      expect(diagnostics()).toEqual([
+        expect.stringContaining('probe inconclusive (EPERM)'),
+      ]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'names a measurement lost to fd exhaustion instead of skipping silently',
+    () => {
+      probe.readdirSync.mockImplementationOnce(refusal('EMFILE', 'scandir'));
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expectProbeCleanedUp();
+      expect(diagnostics()).toEqual([
+        expect.stringMatching(
+          /probe inconclusive \(EMFILE in scandir\) for .+permission-bits\.test\.ts;/,
+        ),
+      ]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'names a temp directory that cannot hold the probe, without throwing',
+    () => {
+      probe.mkdtempSync.mockImplementationOnce(refusal('ENOSPC'));
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expect(probe.chmodSync).not.toHaveBeenCalled();
+      expect(fs.readdirSync(tmp)).toEqual([]);
+      // One whole line, with no workflow command outside GitHub Actions.
+      expect(diagnostics()).toEqual([
+        expect.stringMatching(
+          /^\[permission-bits\] probe inconclusive \(ENOSPC\)[^\n]*\n$/,
+        ),
+      ]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'opens the line with a warning command under GitHub Actions',
+    () => {
+      vi.stubEnv('GITHUB_ACTIONS', 'true');
+      probe.mkdtempSync.mockImplementationOnce(refusal('ENOSPC'));
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      // A workflow command counts only at the start of a line.
+      expect(diagnostics()).toEqual([
+        expect.stringMatching(
+          /^::warning::\[permission-bits\] probe inconclusive \(ENOSPC\)[^\n]*\n$/,
+        ),
+      ]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'answers false, without throwing, when the directory refuses chmod',
+    () => {
+      probe.chmodSync.mockImplementationOnce(refusal('EPERM'));
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expectProbeCleanedUp();
+      expect(diagnostics()).toEqual([
+        expect.stringContaining('probe inconclusive (EPERM)'),
+      ]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'agrees with whether a mode-000 directory refuses this process',
+    () => {
+      const dir = fs.mkdtempSync(path.join(tmp, 'locked-'));
+      fs.chmodSync(dir, 0o000);
+      let refused = false;
+      try {
+        fs.readdirSync(dir);
+      } catch (error) {
+        refused = (error as NodeJS.ErrnoException).code === 'EACCES';
+      } finally {
+        fs.chmodSync(dir, 0o700);
+        fs.rmSync(dir, { recursive: true, force: true });
+      }
+      expect(arePermissionBitsEnforced()).toBe(refused);
+      expect(diagnostics()).toEqual([]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'answers false, without throwing, for a value its diagnostic cannot print',
+    () => {
+      // Thrown where only the diagnostic's own guard stands between it and
+      // a failed test file.
+      probe.chmodSync.mockImplementationOnce(() => {
+        throw Object.assign(Object.create(null), { code: Symbol('odd') });
+      });
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expectProbeCleanedUp();
+      expect(diagnostics()).toEqual([
+        expect.stringContaining('probe inconclusive (an unprintable value)'),
+      ]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'prints an error whose code is not an errno by its message',
+    () => {
+      probe.readdirSync.mockImplementationOnce(() => {
+        throw Object.assign(new Error('odd'), { code: Symbol('odd') });
+      });
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expect(diagnostics()).toEqual([
+        expect.stringContaining('probe inconclusive (Error: odd)'),
+      ]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'still names the errno when its syscall cannot be read',
+    () => {
+      probe.readdirSync.mockImplementationOnce(() => {
+        const error = Object.assign(new Error('EPERM'), { code: 'EPERM' });
+        Object.defineProperty(error, 'syscall', {
+          get() {
+            throw new Error('no syscall');
+          },
+        });
+        throw error;
+      });
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expect(diagnostics()).toEqual([
+        expect.stringContaining('probe inconclusive (EPERM)'),
+      ]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'answers false, without throwing, when stderr itself refuses the line',
+    () => {
+      stderr.mockImplementationOnce(() => {
+        throw Object.assign(new Error('EPIPE'), { code: 'EPIPE' });
+      });
+      // The outer catch reports here, so nothing else stands between the
+      // throwing write and the test file.
+      probe.mkdtempSync.mockImplementationOnce(refusal('ENOSPC'));
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+      expect(fs.readdirSync(tmp)).toEqual([]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'answers, without throwing, when the probe cannot be removed',
+    () => {
+      probe.readdirSync.mockImplementationOnce(refusal('EACCES'));
+      probe.writeFileSync.mockImplementationOnce(refusal('EACCES'));
+      probe.rmSync.mockImplementationOnce(refusal('EBUSY'));
+      expect(arePermissionBitsEnforced(probe)).toBe(true);
+      expect(diagnostics()).toEqual([]);
+    },
+  );
+
+  it.skipIf(process.platform === 'win32')(
+    'answers, without throwing, when the probe mode cannot be restored',
+    () => {
+      probe.readdirSync.mockImplementationOnce(refusal('EACCES'));
+      probe.writeFileSync.mockImplementationOnce(refusal('EACCES'));
+      probe.chmodSync
+        .mockImplementationOnce((file: string, mode: number) =>
+          fs.chmodSync(file, mode),
+        )
+        .mockImplementationOnce(refusal('EPERM'));
+      try {
+        expect(arePermissionBitsEnforced(probe)).toBe(true);
+        expect(diagnostics()).toEqual([]);
+      } finally {
+        // Newer Node versions cannot remove a mode-000 directory, so open
+        // whatever the probe left behind before afterEach clears tmp.
+        const dir = probe.chmodSync.mock.calls[0]?.[0];
+        if (dir !== undefined && fs.existsSync(dir)) fs.chmodSync(dir, 0o700);
+      }
+    },
+  );
+
+  it('answers false on Windows without probing', () => {
+    const platform = Object.getOwnPropertyDescriptor(process, 'platform')!;
+    Object.defineProperty(process, 'platform', { value: 'win32' });
+    try {
+      expect(arePermissionBitsEnforced(probe)).toBe(false);
+    } finally {
+      Object.defineProperty(process, 'platform', platform);
+    }
+    expect(probe.chmodSync).not.toHaveBeenCalled();
+    expect(diagnostics()).toEqual([]);
+  });
+});
diff --git a/packages/browser-use/src/test-utils/permission-bits.ts b/packages/browser-use/src/test-utils/permission-bits.ts
new file mode 100644
index 00000000000..adfa456fea6
--- /dev/null
+++ b/packages/browser-use/src/test-utils/permission-bits.ts
@@ -0,0 +1,135 @@
+/**
+ * @license
+ * Copyright 2026 Qwen Team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { createRequire } from 'node:module';
+import * as path from 'node:path';
+import { expect } from 'vitest';
+
+/** The node:fs calls the probe makes. */
+export interface ProbeFs {
+  mkdtempSync(prefix: string): string;
+  chmodSync(path: string, mode: number): void;
+  readdirSync(path: string): unknown;
+  writeFileSync(path: string, data: string): void;
+  rmSync(path: string, options: { recursive: boolean; force: boolean }): void;
+}
+
+// The real node:fs and node:os, even when the test file that asks has
+// vi.mock()ed them: vitest mocks its own module graph, not a builtin loaded
+// through Node's require. A mocked fs would answer for the mock, not the
+// kernel. A vi.spyOn on node:fs's default export at collection time would
+// still reach the probe, since that export is this same module object.
+const nodeRequire = createRequire(import.meta.url);
+const realFs = nodeRequire('node:fs') as typeof import('node:fs');
+const realOs = nodeRequire('node:os') as typeof import('node:os');
+
+/**
+ * Whether file permission bits bind this process, for tests that force a
+ * failure with `chmod`. They do not on Windows, which ignores Unix-style
+ * bits, nor for root, which bypasses them (on Linux through
+ * CAP_DAC_OVERRIDE and CAP_DAC_READ_SEARCH). ci.yml drops both
+ * capabilities when it runs unit tests as root (package-scripts.test.js
+ * pins that), so asking the kernel, rather than checking for uid 0, keeps
+ * those tests running there. A probe that cannot measure also answers
+ * false, and says so on stderr.
+ * `fs` is for this helper's own tests; every caller probes the real one.
+ */
+export function arePermissionBitsEnforced(fs: ProbeFs = realFs): boolean {
+  if (process.platform === 'win32') return false;
+  let dir: string | undefined;
+  try {
+    dir = fs.mkdtempSync(path.join(realOs.tmpdir(), 'qwen-permission-probe-'));
+    fs.chmodSync(dir, 0o000);
+    const probe = dir;
+    return (
+      refused(() => fs.readdirSync(probe)) &&
+      refused(() => fs.writeFileSync(path.join(probe, 'probe'), ''))
+    );
+  } catch (error) {
+    // A temp directory that cannot hold the probe, or refuses chmod,
+    // cannot hold these tests' fixtures either, though after a transient
+    // ENOSPC it may hold them again by the time they run, so say which it
+    // was rather than skip silently.
+    inconclusive(error);
+    return false;
+  } finally {
+    if (dir !== undefined) {
+      try {
+        fs.chmodSync(dir, 0o700);
+      } catch {
+        // Best effort, like the removal below: newer Node versions refuse
+        // to remove even an empty mode-000 directory.
+      }
+      try {
+        fs.rmSync(dir, { recursive: true, force: true });
+      } catch {
+        // Best effort: a leftover probe must not fail the test file.
+      }
+    }
+  }
+}
+
+function refused(attempt: () => unknown): boolean {
+  try {
+    attempt();
+    return false;
+  } catch (error) {
+    if (errnoOf(error) === 'EACCES') return true;
+    inconclusive(error);
+    return false;
+  }
+}
+
+function errnoOf(error: unknown): string | undefined {
+  const code = attempt(
+    () => (error as NodeJS.ErrnoException | null | undefined)?.code,
+  );
+  return typeof code === 'string' ? code : undefined;
+}
+
+/**
+ * Names a probe that could not measure, and the test file that asked, so
+ * the skips it causes are not mistaken for a Windows or root run. vitest's
+ * `silent: true` drops console output, so this writes to stderr directly.
+ * Under GitHub Actions the line opens with a workflow command, so the skips
+ * show in the check UI and not only deep in the log.
+ */
+function inconclusive(error: unknown): void {
+  try {
+    process.stderr.write(
+      `${process.env['GITHUB_ACTIONS'] === 'true' ? '::warning::' : ''}` +
+        `[permission-bits] probe inconclusive (${causeOf(error)})${askedBy()}; ` +
+        'treating permission bits as unenforced, so chmod-based tests skip\n',
+    );
+  } catch {
+    // A diagnostic must never fail the test file it is meant to explain.
+  }
+}
+
+function causeOf(error: unknown): string {
+  const code = errnoOf(error);
+  if (code === undefined) {
+    return (
+      attempt(() => String(error).split('\n', 1)[0]) ?? 'an unprintable value'
+    );
+  }
+  const syscall = attempt(() => (error as NodeJS.ErrnoException).syscall);
+  return typeof syscall === 'string' ? `${code} in ${syscall}` : code;
+}
+
+function askedBy(): string {
+  const testPath = attempt(() => expect.getState().testPath);
+  if (!testPath) return '';
+  return ` for ${attempt(() => path.relative(process.cwd(), testPath)) ?? testPath}`;
+}
+
+function attempt<T>(read: () => T): T | undefined {
+  try {
+    return read();
+  } catch {
+    return undefined;
+  }
+}
diff --git a/packages/browser-use/tsconfig.declarations.json b/packages/browser-use/tsconfig.declarations.json
index e58637b6aa6..cacd41b02af 100644
--- a/packages/browser-use/tsconfig.declarations.json
+++ b/packages/browser-use/tsconfig.declarations.json
@@ -11,5 +11,5 @@
     "types": ["node"]
   },
   "include": ["src/**/*.ts"],
-  "exclude": ["src/**/*.test.ts", "node_modules", "dist"]
+  "exclude": ["src/**/*.test.ts", "src/test-utils/**", "node_modules", "dist"]
 }
diff --git a/packages/channels/wecom/src/WeComAdapter.test.ts b/packages/channels/wecom/src/WeComAdapter.test.ts
index bce4c214d97..477c29d8a6b 100644
--- a/packages/channels/wecom/src/WeComAdapter.test.ts
+++ b/packages/channels/wecom/src/WeComAdapter.test.ts
@@ -3434,7 +3434,7 @@ describe('WeComChannel', () => {
 
   // The read-only parent only blocks removal where permission bits bind:
   // Windows ignores them and root with its DAC capabilities bypasses them.
-  // Ask the kernel, as the cli and core permission-bits helpers do, so a
+  // Ask the kernel, as the permission-bits helpers in other packages do, so a
   // root lane that drops those capabilities still runs this case. A probe
   // that cannot measure answers false too, and says so on stderr, as a
   // warning under GitHub Actions.
diff --git a/packages/cli/src/serve/local-process-runtime-activator.test.ts b/packages/cli/src/serve/local-process-runtime-activator.test.ts
index dd1fbfd8b06..b295dc9f545 100644
--- a/packages/cli/src/serve/local-process-runtime-activator.test.ts
+++ b/packages/cli/src/serve/local-process-runtime-activator.test.ts
@@ -14,6 +14,7 @@ import {
 } from './local-process-runtime-activator.js';
 import { ProcessRegistry } from '@qwen-code/acp-bridge';
 import type { WorkspaceRuntime } from './workspace-registry.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 const fixture = `
 process.on('message', b => {
@@ -492,7 +493,7 @@ process.on('SIGTERM', () => process.exit(0));
     }
   });
 
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'aggregates a settled rm-class cleanup failure into close()',
     async () => {
       const { activator, stateDir } = await setup(1);
diff --git a/packages/core/src/agents/runtime/workflow-extension.test.ts b/packages/core/src/agents/runtime/workflow-extension.test.ts
index cc72f8c4b8a..165b3af9651 100644
--- a/packages/core/src/agents/runtime/workflow-extension.test.ts
+++ b/packages/core/src/agents/runtime/workflow-extension.test.ts
@@ -14,6 +14,7 @@ import {
   MAX_EXTENSION_WORKFLOW_SCRIPT_BYTES,
 } from './workflow-extension.js';
 import { computeWorkflowScriptDigest } from './workflow-saved.js';
+import { arePermissionBitsEnforced } from '../../test-utils/permission-bits.js';
 
 const isWindows = process.platform === 'win32';
 
@@ -249,11 +250,12 @@ describe('loadExtensionWorkflows', () => {
     ).toEqual([]);
   });
 
-  it.skipIf(isWindows || process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'keeps later declared paths when an earlier one cannot be read',
     async () => {
       await write('good/x.js', workflowSource('x'));
-      await fs.mkdir(path.join(root, 'bad'));
+      // Read, `bad` would add gcp:y, so the result shows it was refused.
+      await write('bad/y.js', workflowSource('y'));
       await fs.chmod(path.join(root, 'bad'), 0o000);
       try {
         expect(await names(['bad', 'good'])).toEqual(['gcp:x']);
diff --git a/packages/core/src/config/managed-session-log.test.ts b/packages/core/src/config/managed-session-log.test.ts
index cbb2b32d04d..a3e9c2726cc 100644
--- a/packages/core/src/config/managed-session-log.test.ts
+++ b/packages/core/src/config/managed-session-log.test.ts
@@ -61,6 +61,7 @@ import {
   localManagedSessionKey,
   managedSessionResourceRoot,
 } from '../utils/sessionStorageUtils.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 const SESSION_ID = '3f2504e0-4f89-41d3-9a0c-0305e82c3301';
 
@@ -639,8 +640,8 @@ describe('Managed Session log recording', () => {
   });
 
   // An unreadable file is made with chmod, which neither Windows nor root
-  // honours.
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  // with its DAC capabilities honours.
+  it.skipIf(!arePermissionBitsEnforced())(
     'keeps a reclaimed lock when it cannot read the log',
     async () => {
       const first = await start(managedConfig());
diff --git a/packages/core/src/ipc/uds-inbox.test.ts b/packages/core/src/ipc/uds-inbox.test.ts
index 963deab35be..20eb8240b28 100644
--- a/packages/core/src/ipc/uds-inbox.test.ts
+++ b/packages/core/src/ipc/uds-inbox.test.ts
@@ -48,6 +48,7 @@ import {
 import type { PeerControllerIdentity } from './peer-controllers.js';
 import { expectWithinLatencyBudget } from '../test-utils/latency-budget.js';
 import { leaveStaleSocket } from '../test-utils/stale-socket.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 /**
  * A PID no process can ever hold.
@@ -331,7 +332,7 @@ describe.skipIf(isWindows)('startPeerInbox', () => {
     expectFailure('path_too_long', 'shorter directory');
   });
 
-  it.skipIf(process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'names the cause when a parent directory is not writable',
     async () => {
       const locked = path.join(tmpDir, 'locked');
@@ -1132,7 +1133,7 @@ describe.skipIf(isWindows)('orphan socket sweeps', () => {
   // it. The existing "keeps a listening socket even when its filename PID
   // is absent" pins only the case where the probe reaches a definitive
   // answer, and stays green whether or not `unknown` is honoured.
-  it.skipIf(process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'keeps a socket whose probe could not reach a verdict',
     async () => {
       const dir = await socksDir();
@@ -1147,7 +1148,7 @@ describe.skipIf(isWindows)('orphan socket sweeps', () => {
     },
   );
 
-  it.skipIf(process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'keeps a fallback directory whose probe could not reach a verdict',
     async () => {
       const parent = await makeShortTmpDir('qwen-inbox-unknown-');
@@ -1401,7 +1402,7 @@ describe.skipIf(isWindows)('PID-keyed path collisions', () => {
     }
   });
 
-  it.skipIf(process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'binds a sibling when the requested path cannot be verified free',
     async () => {
       const taken = sockAt('4242.sock');
@@ -1556,7 +1557,7 @@ describe.skipIf(isWindows)('PID-keyed path collisions', () => {
     }
   });
 
-  it.skipIf(process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'reports sibling overflow when the requested path cannot be verified free',
     async (ctx) => {
       const { root, taken } = await paddedTaken();
diff --git a/packages/core/src/lsp/native-lsp-service.test.ts b/packages/core/src/lsp/native-lsp-service.test.ts
index a1f4a2049d9..0717853fd90 100644
--- a/packages/core/src/lsp/native-lsp-service.test.ts
+++ b/packages/core/src/lsp/native-lsp-service.test.ts
@@ -16,6 +16,7 @@ import * as fs from 'node:fs';
 import * as os from 'node:os';
 import * as path from 'node:path';
 import { pathToFileURL } from 'node:url';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 // 模拟依赖项
 class MockConfig {
@@ -1125,7 +1126,7 @@ describe('NativeLspService', () => {
   // typed cast so the private method need not be public just for tests.
   describe('applyTextEdits — error branches', () => {
     let tmpDir: string;
-    const noChmod = process.platform === 'win32' || process.getuid?.() === 0;
+    const noChmod = !arePermissionBitsEnforced();
 
     const applyEdit = (filePath: string, newText: string) =>
       (
diff --git a/packages/core/src/memory/indexer.test.ts b/packages/core/src/memory/indexer.test.ts
index 3a6a205c336..31188ab6b73 100644
--- a/packages/core/src/memory/indexer.test.ts
+++ b/packages/core/src/memory/indexer.test.ts
@@ -25,6 +25,7 @@ import {
 } from './indexer.js';
 import { ensureAutoMemoryScaffold } from './store.js';
 import * as trustedMemoryFilesystem from './trusted-memory-filesystem.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 vi.mock('./trusted-memory-filesystem.js', { spy: true });
 
@@ -127,40 +128,45 @@ describe('managed auto-memory indexer', () => {
     await expect(fs.readFile(index, 'utf-8')).resolves.toBe('GOOD INDEX\n');
   });
 
-  it('refuses to persist a partial index when a subdirectory cannot be read', async () => {
-    // chmod 000 blocks neither root nor Windows, where a directory chmod only
-    // toggles FILE_ATTRIBUTE_READONLY and so cannot make a directory
-    // unreadable — the rebuild would resolve and the rejects assertion red.
-    if (process.platform === 'win32' || process.getuid?.() === 0) {
-      return;
-    }
-    // A partially walked root must fail the rebuild loudly: the index is the
-    // persisted, authoritative artifact, so committing it from a scan that
-    // silently skipped a directory would drop those entries with no warning.
-    const memoryRoot = getAutoMemoryRoot(projectRoot);
-    const indexPath = getAutoMemoryIndexPath(projectRoot);
-    const doc = (name: string) =>
-      `---\ntype: project\nname: ${name}\ndescription: ${name}\n---\nbody`;
-    const visible = path.join(memoryRoot, 'project', 'visible.md');
-    const locked = path.join(memoryRoot, 'reference');
-    await fs.mkdir(path.dirname(visible), { recursive: true });
-    await fs.writeFile(visible, doc('Visible'), 'utf-8');
-    await fs.mkdir(locked, { recursive: true });
-    await fs.writeFile(path.join(locked, 'hidden.md'), doc('Hidden'), 'utf-8');
-
-    const complete = await rebuildManagedAutoMemoryIndex(projectRoot);
-    expect(complete).toContain('reference/hidden.md');
-
-    await fs.chmod(locked, 0o000);
-    try {
-      await expect(rebuildManagedAutoMemoryIndex(projectRoot)).rejects.toThrow(
-        'memory scan',
+  // chmod 000 blocks neither root with its DAC capabilities nor Windows,
+  // where a directory chmod only toggles FILE_ATTRIBUTE_READONLY and so
+  // cannot make a directory unreadable — the rebuild would resolve and the
+  // rejects assertion red.
+  it.skipIf(!arePermissionBitsEnforced())(
+    'refuses to persist a partial index when a subdirectory cannot be read',
+    async () => {
+      // A partially walked root must fail the rebuild loudly: the index is the
+      // persisted, authoritative artifact, so committing it from a scan that
+      // silently skipped a directory would drop those entries with no warning.
+      const memoryRoot = getAutoMemoryRoot(projectRoot);
+      const indexPath = getAutoMemoryIndexPath(projectRoot);
+      const doc = (name: string) =>
+        `---\ntype: project\nname: ${name}\ndescription: ${name}\n---\nbody`;
+      const visible = path.join(memoryRoot, 'project', 'visible.md');
+      const locked = path.join(memoryRoot, 'reference');
+      await fs.mkdir(path.dirname(visible), { recursive: true });
+      await fs.writeFile(visible, doc('Visible'), 'utf-8');
+      await fs.mkdir(locked, { recursive: true });
+      await fs.writeFile(
+        path.join(locked, 'hidden.md'),
+        doc('Hidden'),
+        'utf-8',
       );
-      await expect(fs.readFile(indexPath, 'utf-8')).resolves.toBe(complete);
-    } finally {
-      await fs.chmod(locked, 0o700);
-    }
-  });
+
+      const complete = await rebuildManagedAutoMemoryIndex(projectRoot);
+      expect(complete).toContain('reference/hidden.md');
+
+      await fs.chmod(locked, 0o000);
+      try {
+        await expect(
+          rebuildManagedAutoMemoryIndex(projectRoot),
+        ).rejects.toThrow('memory scan');
+        await expect(fs.readFile(indexPath, 'utf-8')).resolves.toBe(complete);
+      } finally {
+        await fs.chmod(locked, 0o700);
+      }
+    },
+  );
 
   it('does not create a missing user root while rebuilding', async () => {
     const previousBaseDir = process.env['QWEN_CODE_MEMORY_BASE_DIR'];
diff --git a/packages/core/src/omni/upload-cache.test.ts b/packages/core/src/omni/upload-cache.test.ts
index 9e7c8f59935..bc6e5e9ef5d 100644
--- a/packages/core/src/omni/upload-cache.test.ts
+++ b/packages/core/src/omni/upload-cache.test.ts
@@ -9,6 +9,7 @@ import fs from 'node:fs/promises';
 import os from 'node:os';
 import path from 'node:path';
 import { OmniUploadCache } from './upload-cache.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 let root: string;
 
@@ -25,11 +26,9 @@ afterEach(async () => {
 
 const SHA = 'a'.repeat(64);
 
-// chmod-based denial tests are meaningless on Windows and as root (root
-// bypasses file permission bits).
-const canDropPermissions =
-  process.platform !== 'win32' &&
-  (typeof process.getuid !== 'function' || process.getuid() !== 0);
+// chmod-based denial tests are meaningless where permission bits do not
+// bind: on Windows, and for root with its DAC capabilities.
+const canDropPermissions = arePermissionBitsEnforced();
 
 async function listCorruptBackups(): Promise<string[]> {
   return (await fs.readdir(root)).filter((n) =>
diff --git a/packages/core/src/services/container-execution-transport.test.ts b/packages/core/src/services/container-execution-transport.test.ts
index c88f2365020..807376eeb2f 100644
--- a/packages/core/src/services/container-execution-transport.test.ts
+++ b/packages/core/src/services/container-execution-transport.test.ts
@@ -26,6 +26,7 @@ import { Config } from '../config/config.js';
 import { findProjectRoot } from '../utils/projectRoot.js';
 import { ContainerExecutionEnvironment } from './container-execution-environment.js';
 import type { ExecutionWorkerRequest } from './execution-environment.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 const runtime = vi.hoisted(() => ({ spawn: vi.fn(), execFile: vi.fn() }));
 vi.mock('node:child_process', async (original) => ({
@@ -374,7 +375,7 @@ describe.skipIf(process.platform === 'win32')(
       },
     );
 
-    it.skipIf(process.getuid?.() === 0).each(['mount point', 'output'])(
+    it.skipIf(!arePermissionBitsEnforced()).each(['mount point', 'output'])(
       'retries failed %s deletion without releasing another sibling lease',
       async (target) => {
         const temporary = dirname(environment.outputDirectory);
diff --git a/packages/core/src/services/media-memory/service.test.ts b/packages/core/src/services/media-memory/service.test.ts
index 88003887a76..0de971f556d 100644
--- a/packages/core/src/services/media-memory/service.test.ts
+++ b/packages/core/src/services/media-memory/service.test.ts
@@ -16,6 +16,7 @@ import {
 import { truncateUtf8 } from './service.js';
 import { MEDIA_MEMORY_FILE_NAME } from './store.js';
 import type { MediaMemorySnapshot } from './types.js';
+import { arePermissionBitsEnforced } from '../../test-utils/permission-bits.js';
 
 let root: string;
 let clock: number;
@@ -42,9 +43,7 @@ afterEach(async () => {
   await fs.rm(root, { recursive: true, force: true });
 });
 
-const canDropPermissions =
-  process.platform !== 'win32' &&
-  (typeof process.getuid !== 'function' || process.getuid() !== 0);
+const canDropPermissions = arePermissionBitsEnforced();
 
 async function readSnapshot(): Promise<MediaMemorySnapshot> {
   const raw = await fs.readFile(
diff --git a/packages/core/src/services/media-memory/store.test.ts b/packages/core/src/services/media-memory/store.test.ts
index 880b07faa0d..ed768f0c8dc 100644
--- a/packages/core/src/services/media-memory/store.test.ts
+++ b/packages/core/src/services/media-memory/store.test.ts
@@ -9,6 +9,7 @@ import fs from 'node:fs/promises';
 import os from 'node:os';
 import path from 'node:path';
 import { MediaMemoryStore, MEDIA_MEMORY_FILE_NAME } from './store.js';
+import { arePermissionBitsEnforced } from '../../test-utils/permission-bits.js';
 
 let root: string;
 let store: MediaMemoryStore;
@@ -24,10 +25,9 @@ afterEach(async () => {
   await fs.rm(root, { recursive: true, force: true });
 });
 
-// chmod-based denial tests are meaningless on Windows and as root.
-const canDropPermissions =
-  process.platform !== 'win32' &&
-  (typeof process.getuid !== 'function' || process.getuid() !== 0);
+// chmod-based denial tests are meaningless where permission bits do not
+// bind: on Windows, and for root with its DAC capabilities.
+const canDropPermissions = arePermissionBitsEnforced();
 
 async function listCorruptBackups(): Promise<string[]> {
   return (await fs.readdir(root)).filter((n) =>
diff --git a/packages/core/src/services/ssh-workspace-script.test.ts b/packages/core/src/services/ssh-workspace-script.test.ts
index f2ab306b630..763adf01f8a 100644
--- a/packages/core/src/services/ssh-workspace-script.test.ts
+++ b/packages/core/src/services/ssh-workspace-script.test.ts
@@ -23,6 +23,7 @@ import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { SSH_WORKSPACE_SCRIPT } from './ssh-workspace-script.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 interface Reply {
   ok: boolean;
@@ -631,7 +632,7 @@ describe.skipIf(process.platform === 'win32')('SSH filesystem script', () => {
     );
   });
 
-  it.skipIf(process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'keeps readable results when files and directories deny access',
     () => {
       writeFileSync(join(root, 'visible.txt'), 'needle');
diff --git a/packages/core/src/services/worktreeCleanup.test.ts b/packages/core/src/services/worktreeCleanup.test.ts
index d4227e27841..b08a6a8529f 100644
--- a/packages/core/src/services/worktreeCleanup.test.ts
+++ b/packages/core/src/services/worktreeCleanup.test.ts
@@ -19,6 +19,7 @@ import {
   STALE_WORKTREE_CUTOFF_MS,
   __test__,
 } from './worktreeCleanup.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 const { isEphemeralSlug } = __test__;
 
@@ -561,8 +562,9 @@ describe('cleanupStaleAgentWorktrees', () => {
   });
 
   // chmod-based denial needs POSIX semantics; Windows ACLs do not map, and
-  // root (CI containers) opens mode-000 directories without a warning.
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  // root with its DAC capabilities opens mode-000 directories without a
+  // warning.
+  it.skipIf(!arePermissionBitsEnforced())(
     'preserves a stale worktree when the probe cannot enumerate a directory',
     async () => {
       // `git status` answers a directory it cannot open with a stderr
diff --git a/packages/core/src/tools/record-artifact.test.ts b/packages/core/src/tools/record-artifact.test.ts
index b3cecf3268b..823332c49bc 100644
--- a/packages/core/src/tools/record-artifact.test.ts
+++ b/packages/core/src/tools/record-artifact.test.ts
@@ -24,6 +24,7 @@ import {
   RecordArtifactTool,
   type RecordArtifactParams,
 } from './record-artifact.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 const signal = new AbortController().signal;
 const RES = 'https://example.com/resource';
@@ -456,21 +457,23 @@ describe('RecordArtifactTool', () => {
     );
   });
 
-  it('classifies an unreadable path as permission denied', async () => {
-    if (process.platform === 'win32' || process.getuid?.() === 0) return;
-    const ws = await workspace();
-    await ws.write('hidden/a.csv', 'x');
-    const hidden = path.join(ws.cwd, 'hidden');
-    await chmod(hidden, 0);
-    try {
-      expectFailed(
-        await ws.record('Hidden', 'hidden/a.csv'),
-        ToolErrorType.PERMISSION_DENIED,
-      );
-    } finally {
-      await chmod(hidden, 0o755);
-    }
-  });
+  it.skipIf(!arePermissionBitsEnforced())(
+    'classifies an unreadable path as permission denied',
+    async () => {
+      const ws = await workspace();
+      await ws.write('hidden/a.csv', 'x');
+      const hidden = path.join(ws.cwd, 'hidden');
+      await chmod(hidden, 0);
+      try {
+        expectFailed(
+          await ws.record('Hidden', 'hidden/a.csv'),
+          ToolErrorType.PERMISSION_DENIED,
+        );
+      } finally {
+        await chmod(hidden, 0o755);
+      }
+    },
+  );
 
   it('rejects a wrong workspace-folder prefix instead of reporting success', async () => {
     const ws = await workspace();
diff --git a/packages/core/src/utils/atomicFileWrite.test.ts b/packages/core/src/utils/atomicFileWrite.test.ts
index af9ebfabe24..ca905699afe 100644
--- a/packages/core/src/utils/atomicFileWrite.test.ts
+++ b/packages/core/src/utils/atomicFileWrite.test.ts
@@ -16,6 +16,7 @@ import {
   renameWithRetry,
   renameWithRetrySync,
 } from './atomicFileWrite.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 type AsyncSeams = NonNullable<Parameters<typeof atomicWriteFile>[3]>;
 type SyncSeams = NonNullable<Parameters<typeof atomicWriteFileSync>[3]>;
@@ -373,12 +374,11 @@ describe('atomicWriteFile', () => {
   );
 
   it.skipIf(
-    process.platform === 'win32' ||
-      typeof process.geteuid !== 'function' ||
-      // chmod 0o000 against the file's real owner still succeeds via
-      // POSIX rename in CI/sandbox setups where the user is effectively
-      // root; only assert real EACCES when we own and can be denied.
-      process.geteuid() === 0,
+    typeof process.geteuid !== 'function' ||
+      // The in-place write is refused only where permission bits bind: not
+      // on Windows, nor for root with its DAC capabilities, which writes
+      // the 0o444 file anyway.
+      !arePermissionBitsEnforced(),
   )(
     'should surface EACCES when in-place fallback hits an unwritable file',
     async () => {
diff --git a/packages/core/src/utils/workspace-artifact-directory.test.ts b/packages/core/src/utils/workspace-artifact-directory.test.ts
index 898d2569c55..cfebd3452fe 100644
--- a/packages/core/src/utils/workspace-artifact-directory.test.ts
+++ b/packages/core/src/utils/workspace-artifact-directory.test.ts
@@ -21,6 +21,7 @@ import {
   collectRecordableWorkspaceFiles,
   pathHasSkippedDirectoryComponent,
 } from './workspace-artifact-directory.js';
+import { arePermissionBitsEnforced } from '../test-utils/permission-bits.js';
 
 describe('collectRecordableWorkspaceFiles', () => {
   const dirs: string[] = [];
@@ -145,25 +146,25 @@ describe('collectRecordableWorkspaceFiles', () => {
     expect(collected.depthLimited).toBe(true);
   });
 
-  it('treats an unreadable over-depth directory as depth-limited', async () => {
-    if (process.platform === 'win32' || process.getuid?.() === 0) {
-      return;
-    }
-    const root = await workspace();
-    const deepParts = Array.from(
-      { length: MAX_DIRECTORY_ARTIFACT_DEPTH + 1 },
-      (_, index) => `d${index}`,
-    );
-    const deepDir = path.join(root, ...deepParts);
-    await mkdir(deepDir, { recursive: true });
-    await writeFile(path.join(root, 'shallow.xlsx'), 'shallow');
-    await chmod(deepDir, 0o000);
-    try {
-      const collected = await collectRecordableWorkspaceFiles(root, '', root);
-      expect(collected.files).toEqual(['shallow.xlsx']);
-      expect(collected.depthLimited).toBe(true);
-    } finally {
-      await chmod(deepDir, 0o755);
-    }
-  });
+  it.skipIf(!arePermissionBitsEnforced())(
+    'treats an unreadable over-depth directory as depth-limited',
+    async () => {
+      const root = await workspace();
+      const deepParts = Array.from(
+        { length: MAX_DIRECTORY_ARTIFACT_DEPTH + 1 },
+        (_, index) => `d${index}`,
+      );
+      const deepDir = path.join(root, ...deepParts);
+      await mkdir(deepDir, { recursive: true });
+      await writeFile(path.join(root, 'shallow.xlsx'), 'shallow');
+      await chmod(deepDir, 0o000);
+      try {
+        const collected = await collectRecordableWorkspaceFiles(root, '', root);
+        expect(collected.files).toEqual(['shallow.xlsx']);
+        expect(collected.depthLimited).toBe(true);
+      } finally {
+        await chmod(deepDir, 0o755);
+      }
+    },
+  );
 });
diff --git a/packages/sdk-typescript/test/test-utils/permission-bits.ts b/packages/sdk-typescript/test/test-utils/permission-bits.ts
new file mode 100644
index 00000000000..adfa456fea6
--- /dev/null
+++ b/packages/sdk-typescript/test/test-utils/permission-bits.ts
@@ -0,0 +1,135 @@
+/**
+ * @license
+ * Copyright 2026 Qwen Team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { createRequire } from 'node:module';
+import * as path from 'node:path';
+import { expect } from 'vitest';
+
+/** The node:fs calls the probe makes. */
+export interface ProbeFs {
+  mkdtempSync(prefix: string): string;
+  chmodSync(path: string, mode: number): void;
+  readdirSync(path: string): unknown;
+  writeFileSync(path: string, data: string): void;
+  rmSync(path: string, options: { recursive: boolean; force: boolean }): void;
+}
+
+// The real node:fs and node:os, even when the test file that asks has
+// vi.mock()ed them: vitest mocks its own module graph, not a builtin loaded
+// through Node's require. A mocked fs would answer for the mock, not the
+// kernel. A vi.spyOn on node:fs's default export at collection time would
+// still reach the probe, since that export is this same module object.
+const nodeRequire = createRequire(import.meta.url);
+const realFs = nodeRequire('node:fs') as typeof import('node:fs');
+const realOs = nodeRequire('node:os') as typeof import('node:os');
+
+/**
+ * Whether file permission bits bind this process, for tests that force a
+ * failure with `chmod`. They do not on Windows, which ignores Unix-style
+ * bits, nor for root, which bypasses them (on Linux through
+ * CAP_DAC_OVERRIDE and CAP_DAC_READ_SEARCH). ci.yml drops both
+ * capabilities when it runs unit tests as root (package-scripts.test.js
+ * pins that), so asking the kernel, rather than checking for uid 0, keeps
+ * those tests running there. A probe that cannot measure also answers
+ * false, and says so on stderr.
+ * `fs` is for this helper's own tests; every caller probes the real one.
+ */
+export function arePermissionBitsEnforced(fs: ProbeFs = realFs): boolean {
+  if (process.platform === 'win32') return false;
+  let dir: string | undefined;
+  try {
+    dir = fs.mkdtempSync(path.join(realOs.tmpdir(), 'qwen-permission-probe-'));
+    fs.chmodSync(dir, 0o000);
+    const probe = dir;
+    return (
+      refused(() => fs.readdirSync(probe)) &&
+      refused(() => fs.writeFileSync(path.join(probe, 'probe'), ''))
+    );
+  } catch (error) {
+    // A temp directory that cannot hold the probe, or refuses chmod,
+    // cannot hold these tests' fixtures either, though after a transient
+    // ENOSPC it may hold them again by the time they run, so say which it
+    // was rather than skip silently.
+    inconclusive(error);
+    return false;
+  } finally {
+    if (dir !== undefined) {
+      try {
+        fs.chmodSync(dir, 0o700);
+      } catch {
+        // Best effort, like the removal below: newer Node versions refuse
+        // to remove even an empty mode-000 directory.
+      }
+      try {
+        fs.rmSync(dir, { recursive: true, force: true });
+      } catch {
+        // Best effort: a leftover probe must not fail the test file.
+      }
+    }
+  }
+}
+
+function refused(attempt: () => unknown): boolean {
+  try {
+    attempt();
+    return false;
+  } catch (error) {
+    if (errnoOf(error) === 'EACCES') return true;
+    inconclusive(error);
+    return false;
+  }
+}
+
+function errnoOf(error: unknown): string | undefined {
+  const code = attempt(
+    () => (error as NodeJS.ErrnoException | null | undefined)?.code,
+  );
+  return typeof code === 'string' ? code : undefined;
+}
+
+/**
+ * Names a probe that could not measure, and the test file that asked, so
+ * the skips it causes are not mistaken for a Windows or root run. vitest's
+ * `silent: true` drops console output, so this writes to stderr directly.
+ * Under GitHub Actions the line opens with a workflow command, so the skips
+ * show in the check UI and not only deep in the log.
+ */
+function inconclusive(error: unknown): void {
+  try {
+    process.stderr.write(
+      `${process.env['GITHUB_ACTIONS'] === 'true' ? '::warning::' : ''}` +
+        `[permission-bits] probe inconclusive (${causeOf(error)})${askedBy()}; ` +
+        'treating permission bits as unenforced, so chmod-based tests skip\n',
+    );
+  } catch {
+    // A diagnostic must never fail the test file it is meant to explain.
+  }
+}
+
+function causeOf(error: unknown): string {
+  const code = errnoOf(error);
+  if (code === undefined) {
+    return (
+      attempt(() => String(error).split('\n', 1)[0]) ?? 'an unprintable value'
+    );
+  }
+  const syscall = attempt(() => (error as NodeJS.ErrnoException).syscall);
+  return typeof syscall === 'string' ? `${code} in ${syscall}` : code;
+}
+
+function askedBy(): string {
+  const testPath = attempt(() => expect.getState().testPath);
+  if (!testPath) return '';
+  return ` for ${attempt(() => path.relative(process.cwd(), testPath)) ?? testPath}`;
+}
+
+function attempt<T>(read: () => T): T | undefined {
+  try {
+    return read();
+  } catch {
+    return undefined;
+  }
+}
diff --git a/packages/sdk-typescript/test/unit/peer/registry.test.ts b/packages/sdk-typescript/test/unit/peer/registry.test.ts
index c8116ade11f..8393aca2ed8 100644
--- a/packages/sdk-typescript/test/unit/peer/registry.test.ts
+++ b/packages/sdk-typescript/test/unit/peer/registry.test.ts
@@ -22,6 +22,7 @@ import {
   type SessionRecord,
   writeOwnRecord,
 } from '../../../src/peer/registry.js';
+import { arePermissionBitsEnforced } from '../../test-utils/permission-bits.js';
 
 const isPosix = process.platform !== 'win32';
 const isLinux = process.platform === 'linux';
@@ -274,7 +275,7 @@ describe('writeOwnRecord — defensive paths', () => {
     },
   );
 
-  it.runIf(isPosix && process.getuid?.() !== 0)(
+  it.runIf(arePermissionBitsEnforced())(
     'does not replace a record it merely failed to read',
     async () => {
       const shared = plant(
diff --git a/scripts/tests/check-tui-dep-direction.test.js b/scripts/tests/check-tui-dep-direction.test.js
index 50bc812b310..03a73430453 100644
--- a/scripts/tests/check-tui-dep-direction.test.js
+++ b/scripts/tests/check-tui-dep-direction.test.js
@@ -27,6 +27,7 @@ import {
   listSourceFiles,
   symlinkedPathComponents,
 } from '../check-tui-dep-direction.mjs';
+import { arePermissionBitsEnforced } from '../../packages/cli/src/test-utils/permission-bits.js';
 
 const temporaryDirectories = [];
 
@@ -435,7 +436,7 @@ describe('checkRule', () => {
     expect(otherRule.violations).toEqual([]);
   });
 
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'reports unlistable directories instead of silently dropping them',
     () => {
       const root = makeTemporaryDirectory();
@@ -709,7 +710,7 @@ describe('end-to-end gate run (main wiring)', () => {
     expect(out).toContain('not found or has no source files');
   }, 40000);
 
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'fails on an unlistable directory inside the scanned tree',
     () => {
       const base = makeFixtureCheckout();
diff --git a/scripts/tests/package-assets.test.js b/scripts/tests/package-assets.test.js
index 612a010d634..7b3d76427e9 100644
--- a/scripts/tests/package-assets.test.js
+++ b/scripts/tests/package-assets.test.js
@@ -25,6 +25,7 @@ import {
 } from '../copy_bundle_assets.js';
 import { copyFiles } from '../copy_files.js';
 import { preparePackage } from '../prepare-package.js';
+import { arePermissionBitsEnforced } from '../../packages/cli/src/test-utils/permission-bits.js';
 
 const realReadFileSync = fs.readFileSync;
 const realReaddirSync = fs.readdirSync;
@@ -569,12 +570,12 @@ describe('package asset scripts', () => {
     ).toBe(false);
   });
 
-  // chmod is the only lever this case has: on Windows it is a no-op, and a
-  // root user reads through it, so the branch under test is unreachable
-  // there. The case skips rather than running into the other branch — a
-  // readable tree, stamped as usual — and failing red against the no-stamp
-  // assertion.
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  // chmod is the only lever this case has: on Windows it is a no-op, and
+  // root with its DAC capabilities reads through it, so the branch under
+  // test is unreachable there. The case skips rather than running into the
+  // other branch — a readable tree, stamped as usual — and failing red
+  // against the no-stamp assertion.
+  it.skipIf(!arePermissionBitsEnforced())(
     'refuses when a digest root exists but cannot be listed',
     () => {
       // The root-level arm of the unlistable-directory refusal: with the
diff --git a/scripts/tests/package-scripts.test.js b/scripts/tests/package-scripts.test.js
index 7b829cf5403..162558c7015 100644
--- a/scripts/tests/package-scripts.test.js
+++ b/scripts/tests/package-scripts.test.js
@@ -1158,9 +1158,9 @@ describe('package scripts', () => {
   });
 
   it('drops DAC capabilities for root unit tests on both CI commands', () => {
-    // The permission-bit gates in packages/cli, packages/core,
-    // packages/channels/wecom and scripts/tests ask the kernel, so on a root
-    // lane that keeps these capabilities they all skip, without failing.
+    // The permission-bit probes in the workspaces and scripts/tests ask the
+    // kernel, so on a root lane that keeps these capabilities every case
+    // they gate skips, without failing.
     const step = getWorkflowStep(
       getWorkflowJob(readWorkflow('.github/workflows/ci.yml'), 'test'),
       'Run tests and generate reports',
@@ -1198,6 +1198,40 @@ describe('package scripts', () => {
     ).toHaveLength(2);
   });
 
+  it('keeps every copy of the permission-bit probe identical', () => {
+    // The probe is copied, not shared: each package that uses it keeps its
+    // own copy, and cli, core and browser-use also keep its tests (wecom
+    // inlines a smaller probe for its one case). A fix to one copy has to
+    // reach the others, or the packages measure differently.
+    const copies = {
+      'permission-bits.ts': [
+        'packages/cli/src/test-utils',
+        'packages/core/src/test-utils',
+        'packages/browser-use/src/test-utils',
+        'packages/sdk-typescript/test/test-utils',
+        'integrations/test-failure-explorer/src/test-utils',
+      ],
+      'permission-bits.test.ts': [
+        'packages/cli/src/test-utils',
+        'packages/core/src/test-utils',
+        'packages/browser-use/src/test-utils',
+      ],
+      'permission-bits.mocked-fs.test.ts': [
+        'packages/cli/src/test-utils',
+        'packages/core/src/test-utils',
+        'packages/browser-use/src/test-utils',
+      ],
+    };
+    for (const [file, dirs] of Object.entries(copies)) {
+      const [reference, ...others] = dirs.map((dir) =>
+        readFileSync(path.join(root, dir, file), 'utf8'),
+      );
+      others.forEach((text, i) => {
+        expect(text, `${file}: ${dirs[i + 1]} vs ${dirs[0]}`).toBe(reference);
+      });
+    }
+  });
+
   it('bounds the CI unit step so a hang fails instead of stalling', () => {
     // #10490's run 3 was cancelled at ~60 minutes, leaving behind
     // orphaned test processes; a stall reads as a timeout, not a failure.
diff --git a/scripts/tests/qwen-pr-review-workflow.test.js b/scripts/tests/qwen-pr-review-workflow.test.js
index b4bfbe8dd5a..aef0806b7e8 100644
--- a/scripts/tests/qwen-pr-review-workflow.test.js
+++ b/scripts/tests/qwen-pr-review-workflow.test.js
@@ -3427,7 +3427,8 @@ describe('checkout self-heal', () => {
   // A workspace whose entries the owning user cannot unlink: find -exec rm
   // exits nonzero, so the user-mode wipe leg fails deterministically. Root
   // bypasses the 0o500 lock via CAP_DAC_OVERRIDE, so the tests built on it
-  // skip there, and win32 has no POSIX permission bits to honor.
+  // skip where it keeps that capability, and win32 has no POSIX permission
+  // bits to honor.
   const lockFixture = () => {
     const parent = realpathSync(
       mkdtempSync(join(tmpdir(), 'checkout-heal-lock-')),
@@ -3443,7 +3444,7 @@ describe('checkout self-heal', () => {
     rmSync(parent, { recursive: true, force: true });
   };
 
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'exits 0 and keeps survivors when BOTH wipe legs fail',
     () => {
       // The wipe step has no continue-on-error, so its own never-fail exit
@@ -3473,7 +3474,7 @@ describe('checkout self-heal', () => {
     },
   );
 
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  it.skipIf(!arePermissionBitsEnforced())(
     'escalates to the sudo leg when the user-mode wipe fails',
     () => {
       // Deleting the `|| sudo -n find …` leg (or flipping it to `&&`) must
diff --git a/scripts/tests/qwen-triage-workflow.test.js b/scripts/tests/qwen-triage-workflow.test.js
index 0368cfb5ed3..5c7f57dd912 100644
--- a/scripts/tests/qwen-triage-workflow.test.js
+++ b/scripts/tests/qwen-triage-workflow.test.js
@@ -21,6 +21,7 @@ import { tmpdir } from 'node:os';
 import { basename, join } from 'node:path';
 import { describe, expect, it } from 'vitest';
 import { parse } from 'yaml';
+import { arePermissionBitsEnforced } from '../../packages/cli/src/test-utils/permission-bits.js';
 
 const workflow = readFileSync('.github/workflows/qwen-triage.yml', 'utf8');
 const cacheProducerWorkflow = readFileSync(
@@ -2284,12 +2285,13 @@ describe('qwen-triage verify hardening', () => {
     },
   );
 
-  it.skipIf(!hasGnuRealpath || process.getuid?.() === 0)(
+  it.skipIf(!hasGnuRealpath || !arePermissionBitsEnforced())(
     'fails closed when the corrupt workspace cannot be unlinked',
     () => {
       // A swallowed `rm -f` failure would let the mkdir and the wipe run on
-      // a path that is still a symlink. Root bypasses the mode bits, so the
-      // fixture cannot produce the refusal there.
+      // a path that is still a symlink. Root with its DAC capabilities
+      // bypasses the mode bits, so the fixture cannot produce the refusal
+      // there.
       for (const stepName of WIPE_STEPS) {
         const parent = mkdtempSync(join(tmpdir(), 'verify-heal-perm-'));
         const outside = mkdtempSync(join(tmpdir(), 'verify-heal-outside-'));
diff --git a/scripts/tests/review-source-digest.test.ts b/scripts/tests/review-source-digest.test.ts
index 7fdebb7aaeb..6c0bce58642 100644
--- a/scripts/tests/review-source-digest.test.ts
+++ b/scripts/tests/review-source-digest.test.ts
@@ -43,6 +43,7 @@ import {
   reviewSourceRoots,
   reviewSourcesDigest,
 } from '../../packages/cli/src/commands/review/lib/stale-bundle.js';
+import { arePermissionBitsEnforced } from '../../packages/cli/src/test-utils/permission-bits.js';
 
 const repoRoot = join(fileURLToPath(new URL('.', import.meta.url)), '..', '..');
 
@@ -228,11 +229,12 @@ describe('the build stamp and the staleness check agree', () => {
     }
   });
 
-  // chmod is the only lever this case has: on Windows it is a no-op, and a
-  // root user reads through it, so the branch under test is unreachable
-  // there. The case skips rather than measuring a readable tree and failing
-  // red against the throw-and-nothing-measured assertions.
-  it.skipIf(process.platform === 'win32' || process.getuid?.() === 0)(
+  // chmod is the only lever this case has: on Windows it is a no-op, and
+  // root with its DAC capabilities reads through it, so the branch under
+  // test is unreachable there. The case skips rather than measuring a
+  // readable tree and failing red against the throw-and-nothing-measured
+  // assertions.
+  it.skipIf(!arePermissionBitsEnforced())(
     'neither side measures a tree whose subdirectory cannot be listed',
     () => {
       // The unreadable-DIRECTORY case, on both sides of the boundary at once:
diff --git a/scripts/tests/review-worktree-cleanup-workflow.test.js b/scripts/tests/review-worktree-cleanup-workflow.test.js
index a3df45bdeca..c00ae3c518d 100644
--- a/scripts/tests/review-worktree-cleanup-workflow.test.js
+++ b/scripts/tests/review-worktree-cleanup-workflow.test.js
@@ -28,6 +28,7 @@ import {
   reviewBranch,
   worktreePath,
 } from '../../packages/cli/src/commands/review/lib/paths.js';
+import { arePermissionBitsEnforced } from '../../packages/cli/src/test-utils/permission-bits.js';
 
 // The cleanup steps in ci.yml and qwen-code-pr-review.yml hard-code the
 // review-artifact layout owned by paths.ts: worktreePath()/reviewBranch()
@@ -191,13 +192,13 @@ function expectQuarantineFallback(run) {
   // guard's `! -L` arm is what keeps `chmod -R u+w` from dereferencing a
   // symlinked leftover into a tree outside the workspace. The behavioral
   // fixtures below execute both copies where permission fixtures are
-  // available (skipped on the Windows/root lanes): the dangling-symlink
-  // fixture witnesses the existence guard's `-L` arm behaviorally on each
-  // copy, but the chmod guard's `! -L` arm has no behavioral witness (the
-  // live-symlink fixture asserts content, not mode), so pin both arms
-  // textually here on every copy — dropping `-L` fails the dangling-symlink
-  // fixture, while dropping `! -L` keeps this suite green and re-poisons
-  // the checkout (mutation-probed).
+  // available (skipped on Windows, and for root with its DAC capabilities):
+  // the dangling-symlink fixture witnesses the existence guard's `-L` arm
+  // behaviorally on each copy, but the chmod guard's `! -L` arm has no
+  // behavioral witness (the live-symlink fixture asserts content, not
+  // mode), so pin both arms textually here on every copy — dropping `-L`
+  // fails the dangling-symlink fixture, while dropping `! -L` keeps this
+  // suite green and re-poisons the checkout (mutation-probed).
   expect(code).toContain('[ ! -e "$stale_qwen" ] && [ ! -L "$stale_qwen" ]');
   expect(code).toContain('[ -d "$stale_qwen" ] && [ ! -L "$stale_qwen" ]');
   // The move must be the fallback of the removal chain, not an
@@ -263,9 +264,9 @@ const sweepToolsAvailable =
   ).status === 0;
 // The fixtures defeat rm with a chmod-555 parent, which needs POSIX
 // permission semantics: Git Bash on Windows resolves `bash` but not chmod,
-// and root ignores the bits entirely.
+// and root with its DAC capabilities ignores the bits entirely.
 const permissionFixturesAvailable =
-  bashAvailable && process.platform !== 'win32' && process.geteuid?.() !== 0;
+  bashAvailable && arePermissionBitsEnforced();
 // The ladder's failure path resolves the leftover with `realpath --`; on a
 // host without it (the merge_group macOS lane ships none) the function
 // refuses as `path could not be resolved` instead, so the test asserting
diff --git a/scripts/tests/serve-ab-workflow.test.js b/scripts/tests/serve-ab-workflow.test.js
index a50f74f11bb..d76897fee78 100644
--- a/scripts/tests/serve-ab-workflow.test.js
+++ b/scripts/tests/serve-ab-workflow.test.js
@@ -22,6 +22,7 @@ import { tmpdir } from 'node:os';
 import { basename, dirname, join } from 'node:path';
 import { describe, expect, it } from 'vitest';
 import { parse } from 'yaml';
+import { arePermissionBitsEnforced } from '../../packages/cli/src/test-utils/permission-bits.js';
 
 const workflow = readFileSync('.github/workflows/serve-ab.yml', 'utf8');
 
@@ -744,12 +745,13 @@ describe('serve-ab pre-checkout workspace wipe', () => {
     },
   );
 
-  it.skipIf(!hasGnuRealpath || process.getuid?.() === 0)(
+  it.skipIf(!hasGnuRealpath || !arePermissionBitsEnforced())(
     'fails closed when the corrupt workspace cannot be unlinked',
     () => {
       // A swallowed `rm -f` failure would let the mkdir and the wipe run on
-      // a path that is still a symlink. Root bypasses the mode bits, so the
-      // fixture cannot produce the refusal there.
+      // a path that is still a symlink. Root with its DAC capabilities
+      // bypasses the mode bits, so the fixture cannot produce the refusal
+      // there.
       const parent = mkdtempSync(join(tmpdir(), 'serve-ab-heal-perm-'));
       const outside = mkdtempSync(join(tmpdir(), 'serve-ab-heal-outside-'));
       const ws = join(parent, 'repo');