diff --git a/extensions/browser/src/browser/chrome.default-browser.test.ts b/extensions/browser/src/browser/chrome.default-browser.test.ts
index 33d92f7f124..e2f2465a133 100644
--- a/extensions/browser/src/browser/chrome.default-browser.test.ts
+++ b/extensions/browser/src/browser/chrome.default-browser.test.ts
@@ -1,33 +1,25 @@
 import { beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
 
 vi.mock("node:child_process", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:child_process")>();
-  return {
-    ...actual,
+  const { mockNodeBuiltinModule } = await import("../../../../test/helpers/node-builtin-mocks.js");
+  return mockNodeBuiltinModule(importOriginal, {
     execFileSync: vi.fn(),
-  };
+  });
 });
 vi.mock("node:fs", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:fs")>();
+  const { mockNodeBuiltinModule } = await import("../../../../test/helpers/node-builtin-mocks.js");
   const existsSync = vi.fn();
   const readFileSync = vi.fn();
-  const module = { existsSync, readFileSync };
-  return {
-    ...actual,
-    ...module,
-    default: {
-      ...actual,
-      ...module,
-    },
-  };
+  return mockNodeBuiltinModule(
+    importOriginal,
+    { existsSync, readFileSync },
+    { mirrorToDefault: true },
+  );
 });
-vi.mock("node:os", () => {
+vi.mock("node:os", async (importOriginal) => {
+  const { mockNodeBuiltinModule } = await import("../../../../test/helpers/node-builtin-mocks.js");
   const homedir = vi.fn();
-  const module = { homedir };
-  return {
-    ...module,
-    default: module,
-  };
+  return mockNodeBuiltinModule(importOriginal, { homedir }, { mirrorToDefault: true });
 });
 import { execFileSync } from "node:child_process";
 import * as fs from "node:fs";
diff --git a/scripts/test-projects.mjs b/scripts/test-projects.mjs
index af569deabff..f74320e349b 100644
--- a/scripts/test-projects.mjs
+++ b/scripts/test-projects.mjs
@@ -3,6 +3,8 @@ import { acquireLocalHeavyCheckLockSync } from "./lib/local-heavy-check-runtime.
 import { spawnPnpmRunner } from "./pnpm-runner.mjs";
 import { createVitestRunSpecs, writeVitestIncludeFile } from "./test-projects.test-support.mjs";
 
+// Keep this shim so `pnpm test -- src/foo.test.ts` still forwards filters
+// cleanly instead of leaking pnpm's passthrough sentinel to Vitest.
 const releaseLock = acquireLocalHeavyCheckLockSync({
   cwd: process.cwd(),
   env: process.env,
diff --git a/src/infra/gateway-processes.test.ts b/src/infra/gateway-processes.test.ts
index 67964d7661d..c3418f4516e 100644
--- a/src/infra/gateway-processes.test.ts
+++ b/src/infra/gateway-processes.test.ts
@@ -8,23 +8,21 @@ const isGatewayArgvMock = vi.hoisted(() => vi.fn());
 const findGatewayPidsOnPortSyncMock = vi.hoisted(() => vi.fn());
 
 vi.mock("node:child_process", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:child_process")>();
-  return {
-    ...actual,
+  const { mockNodeBuiltinModule } = await import("../../test/helpers/node-builtin-mocks.js");
+  return mockNodeBuiltinModule(importOriginal, {
     spawnSync: (...args: unknown[]) => spawnSyncMock(...args),
-  };
+  });
 });
 
 vi.mock("node:fs", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:fs")>();
-  return {
-    ...actual,
-    default: {
-      ...actual,
+  const { mockNodeBuiltinModule } = await import("../../test/helpers/node-builtin-mocks.js");
+  return mockNodeBuiltinModule(
+    importOriginal,
+    {
       readFileSync: (...args: unknown[]) => readFileSyncMock(...args),
     },
-    readFileSync: (...args: unknown[]) => readFileSyncMock(...args),
-  };
+    { mirrorToDefault: true },
+  );
 });
 
 vi.mock("../daemon/cmd-argv.js", () => ({
diff --git a/src/infra/ssh-config.test.ts b/src/infra/ssh-config.test.ts
index 01d40fa85f6..db1c34255da 100644
--- a/src/infra/ssh-config.test.ts
+++ b/src/infra/ssh-config.test.ts
@@ -17,7 +17,7 @@ function createMockSpawnChild() {
 }
 
 vi.mock("node:child_process", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:child_process")>();
+  const { mockNodeBuiltinModule } = await import("../../test/helpers/node-builtin-mocks.js");
   const spawn = vi.fn(() => {
     const { child, stdout } = createMockSpawnChild();
     process.nextTick(() => {
@@ -36,10 +36,9 @@ vi.mock("node:child_process", async (importOriginal) => {
     });
     return child;
   });
-  return {
-    ...actual,
+  return mockNodeBuiltinModule(importOriginal, {
     spawn,
-  };
+  });
 });
 
 const spawnMock = vi.mocked(spawn);
diff --git a/src/infra/windows-task-restart.test.ts b/src/infra/windows-task-restart.test.ts
index ce6f8cd8da9..1f4177350e8 100644
--- a/src/infra/windows-task-restart.test.ts
+++ b/src/infra/windows-task-restart.test.ts
@@ -8,11 +8,10 @@ const spawnMock = vi.hoisted(() => vi.fn());
 const resolvePreferredOpenClawTmpDirMock = vi.hoisted(() => vi.fn(() => os.tmpdir()));
 
 vi.mock("node:child_process", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:child_process")>();
-  return {
-    ...actual,
+  const { mockNodeBuiltinModule } = await import("../../test/helpers/node-builtin-mocks.js");
+  return mockNodeBuiltinModule(importOriginal, {
     spawn: (...args: unknown[]) => spawnMock(...args),
-  };
+  });
 });
 vi.mock("./tmp-openclaw-dir.js", () => ({
   resolvePreferredOpenClawTmpDir: () => resolvePreferredOpenClawTmpDirMock(),
diff --git a/src/plugin-sdk/browser-maintenance.test.ts b/src/plugin-sdk/browser-maintenance.test.ts
index 630301bc429..48a5f2510b4 100644
--- a/src/plugin-sdk/browser-maintenance.test.ts
+++ b/src/plugin-sdk/browser-maintenance.test.ts
@@ -15,31 +15,21 @@ vi.mock("./facade-runtime.js", () => ({
 }));
 
 vi.mock("node:fs/promises", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:fs/promises")>();
-  return {
-    ...actual,
-    default: {
-      ...actual,
-      mkdir,
-      access,
-      rename,
-    },
-    mkdir,
-    access,
-    rename,
-  };
+  const { mockNodeBuiltinModule } = await import("../../test/helpers/node-builtin-mocks.js");
+  return mockNodeBuiltinModule(
+    importOriginal,
+    { mkdir, access, rename },
+    { mirrorToDefault: true },
+  );
 });
 
 vi.mock("node:os", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:os")>();
-  return {
-    ...actual,
-    default: {
-      ...actual,
-      homedir: () => "/home/test",
-    },
-    homedir: () => "/home/test",
-  };
+  const { mockNodeBuiltinModule } = await import("../../test/helpers/node-builtin-mocks.js");
+  return mockNodeBuiltinModule(
+    importOriginal,
+    { homedir: () => "/home/test" },
+    { mirrorToDefault: true },
+  );
 });
 
 describe("browser maintenance", () => {
diff --git a/src/process/exec.windows.test.ts b/src/process/exec.windows.test.ts
index 537404e54d2..202e4372976 100644
--- a/src/process/exec.windows.test.ts
+++ b/src/process/exec.windows.test.ts
@@ -7,12 +7,11 @@ const spawnMock = vi.hoisted(() => vi.fn());
 const execFileMock = vi.hoisted(() => vi.fn());
 
 vi.mock("node:child_process", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:child_process")>();
-  return {
-    ...actual,
+  const { mockNodeBuiltinModule } = await import("../../test/helpers/node-builtin-mocks.js");
+  return mockNodeBuiltinModule(importOriginal, {
     spawn: spawnMock,
     execFile: execFileMock,
-  };
+  });
 });
 
 let runCommandWithTimeout: typeof import("./exec.js").runCommandWithTimeout;
diff --git a/src/security/windows-acl.test.ts b/src/security/windows-acl.test.ts
index fc144c6c34d..369f97a8cb8 100644
--- a/src/security/windows-acl.test.ts
+++ b/src/security/windows-acl.test.ts
@@ -4,16 +4,12 @@ import type { WindowsAclEntry, WindowsAclSummary } from "./windows-acl.js";
 const MOCK_USERNAME = "MockUser";
 
 vi.mock("node:os", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("node:os")>();
-  const base = ("default" in actual ? actual.default : actual) as Record<string, unknown>;
-  return {
-    ...actual,
-    default: {
-      ...base,
-      userInfo: () => ({ username: MOCK_USERNAME }),
-    },
-    userInfo: () => ({ username: MOCK_USERNAME }),
-  };
+  const { mockNodeBuiltinModule } = await import("../../test/helpers/node-builtin-mocks.js");
+  return mockNodeBuiltinModule(
+    importOriginal,
+    { userInfo: () => ({ username: MOCK_USERNAME }) },
+    { mirrorToDefault: true },
+  );
 });
 
 let createIcaclsResetCommand: typeof import("./windows-acl.js").createIcaclsResetCommand;
diff --git a/test/extension-test-boundary.test.ts b/test/extension-test-boundary.test.ts
index 834299ba686..5e2dc581fbe 100644
--- a/test/extension-test-boundary.test.ts
+++ b/test/extension-test-boundary.test.ts
@@ -34,6 +34,24 @@ function walk(dir: string, entries: string[] = []): string[] {
   return entries;
 }
 
+function walkCode(dir: string, entries: string[] = []): string[] {
+  for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+    const fullPath = path.join(dir, entry.name);
+    if (entry.isDirectory()) {
+      if (entry.name === "node_modules" || entry.name === "dist" || entry.name === ".git") {
+        continue;
+      }
+      walkCode(fullPath, entries);
+      continue;
+    }
+    if (!entry.name.endsWith(".ts") && !entry.name.endsWith(".tsx")) {
+      continue;
+    }
+    entries.push(path.relative(repoRoot, fullPath).replaceAll(path.sep, "/"));
+  }
+  return entries;
+}
+
 function findExtensionImports(source: string): string[] {
   return [
     ...source.matchAll(/from\s+["']((?:\.\.\/)+extensions\/[^"']+)["']/g),
@@ -124,4 +142,21 @@ describe("non-extension test boundaries", () => {
 
     expect(imports).toEqual([]);
   });
+
+  it("keeps bundled plugin sync test-api loaders out of core tests", () => {
+    const files = [
+      ...walkCode(path.join(repoRoot, "src")),
+      ...walkCode(path.join(repoRoot, "test")),
+    ]
+      .filter((file) => !file.startsWith(BUNDLED_PLUGIN_PATH_PREFIX))
+      .filter((file) => !file.startsWith("test/helpers/"))
+      .filter((file) => file !== "test/extension-test-boundary.test.ts");
+
+    const offenders = files.filter((file) => {
+      const source = fs.readFileSync(path.join(repoRoot, file), "utf8");
+      return source.includes("loadBundledPluginTestApiSync(");
+    });
+
+    expect(offenders).toEqual([]);
+  });
 });
diff --git a/test/helpers/node-builtin-mocks.test.ts b/test/helpers/node-builtin-mocks.test.ts
new file mode 100644
index 00000000000..8d6b7d156c3
--- /dev/null
+++ b/test/helpers/node-builtin-mocks.test.ts
@@ -0,0 +1,54 @@
+import { describe, expect, it } from "vitest";
+import { mockNodeBuiltinModule } from "./node-builtin-mocks.js";
+
+describe("mockNodeBuiltinModule", () => {
+  it("merges partial overrides into the original module", async () => {
+    const actual = { readFileSync: () => "actual", watch: () => "watch" };
+    const readFileSync = () => "mock";
+
+    const mocked = await mockNodeBuiltinModule(async () => actual, {
+      readFileSync,
+    });
+
+    expect(mocked.readFileSync).toBe(readFileSync);
+    expect(mocked.watch).toBe(actual.watch);
+    expect("default" in mocked).toBe(false);
+  });
+
+  it("mirrors overrides into the default export when requested", async () => {
+    const homedir = () => "/tmp/home";
+
+    const mocked = await mockNodeBuiltinModule(
+      async () => ({ tmpdir: () => "/tmp" }),
+      { homedir },
+      { mirrorToDefault: true },
+    );
+
+    expect(mocked.default).toMatchObject({
+      homedir,
+      tmpdir: expect.any(Function),
+    });
+  });
+
+  it("preserves existing default exports while overriding members", async () => {
+    const actual = {
+      readFileSync: () => "actual",
+      default: {
+        readFileSync: () => "actual",
+        statSync: () => "stat",
+      },
+    };
+    const readFileSync = () => "mock";
+
+    const mocked = await mockNodeBuiltinModule(
+      async () => actual,
+      { readFileSync },
+      { mirrorToDefault: true },
+    );
+
+    expect(mocked.default).toMatchObject({
+      readFileSync,
+      statSync: expect.any(Function),
+    });
+  });
+});
diff --git a/test/helpers/node-builtin-mocks.ts b/test/helpers/node-builtin-mocks.ts
new file mode 100644
index 00000000000..a35d3118236
--- /dev/null
+++ b/test/helpers/node-builtin-mocks.ts
@@ -0,0 +1,43 @@
+type MockFactory<TModule extends object> =
+  | Partial<TModule>
+  | ((actual: TModule) => Partial<TModule>);
+
+function resolveMockOverrides<TModule extends object>(
+  actual: TModule,
+  factory: MockFactory<TModule>,
+): Partial<TModule> {
+  return typeof factory === "function" ? factory(actual) : factory;
+}
+
+function resolveDefaultBase<TModule extends object>(actual: TModule): Record<string, unknown> {
+  const defaultExport = (actual as TModule & { default?: unknown }).default;
+  if (defaultExport && typeof defaultExport === "object") {
+    return defaultExport as Record<string, unknown>;
+  }
+  return actual as Record<string, unknown>;
+}
+
+export async function mockNodeBuiltinModule<TModule extends object>(
+  importOriginal: () => Promise<TModule>,
+  factory: MockFactory<TModule>,
+  options?: { mirrorToDefault?: boolean },
+): Promise<TModule> {
+  const actual = await importOriginal();
+  const overrides = resolveMockOverrides(actual, factory);
+  const mocked = {
+    ...actual,
+    ...overrides,
+  } as TModule & { default?: Record<string, unknown> };
+
+  if (!options?.mirrorToDefault) {
+    return mocked;
+  }
+
+  return {
+    ...mocked,
+    default: {
+      ...resolveDefaultBase(actual),
+      ...overrides,
+    },
+  } as TModule;
+}