diff --git a/test/vitest-performance-config.test.ts b/test/vitest-performance-config.test.ts
index 4766b6cf27..aac2533012 100644
--- a/test/vitest-performance-config.test.ts
+++ b/test/vitest-performance-config.test.ts
@@ -3,7 +3,7 @@ import { loadVitestExperimentalConfig } from "../vitest.performance-config.ts";
 
 describe("loadVitestExperimentalConfig", () => {
   it("enables the filesystem module cache by default", () => {
-    expect(loadVitestExperimentalConfig({})).toEqual({
+    expect(loadVitestExperimentalConfig({}, "linux")).toEqual({
       experimental: {
         fsModuleCache: true,
       },
@@ -12,9 +12,12 @@ describe("loadVitestExperimentalConfig", () => {
 
   it("enables the filesystem module cache explicitly", () => {
     expect(
-      loadVitestExperimentalConfig({
-        OPENCLAW_VITEST_FS_MODULE_CACHE: "1",
-      }),
+      loadVitestExperimentalConfig(
+        {
+          OPENCLAW_VITEST_FS_MODULE_CACHE: "1",
+        },
+        "linux",
+      ),
     ).toEqual({
       experimental: {
         fsModuleCache: true,
@@ -23,56 +26,44 @@ describe("loadVitestExperimentalConfig", () => {
   });
 
   it("disables the filesystem module cache by default on Windows", () => {
-    const originalRunnerOs = process.env.RUNNER_OS;
-    process.env.RUNNER_OS = "Windows";
-    try {
-      expect(loadVitestExperimentalConfig({ RUNNER_OS: "Windows" })).toEqual({});
-    } finally {
-      if (originalRunnerOs === undefined) {
-        delete process.env.RUNNER_OS;
-      } else {
-        process.env.RUNNER_OS = originalRunnerOs;
-      }
-    }
+    expect(loadVitestExperimentalConfig({}, "win32")).toEqual({});
   });
 
   it("still allows enabling the filesystem module cache explicitly on Windows", () => {
-    const originalRunnerOs = process.env.RUNNER_OS;
-    process.env.RUNNER_OS = "Windows";
-    try {
-      expect(
-        loadVitestExperimentalConfig({
-          RUNNER_OS: "Windows",
+    expect(
+      loadVitestExperimentalConfig(
+        {
           OPENCLAW_VITEST_FS_MODULE_CACHE: "1",
-        }),
-      ).toEqual({
-        experimental: {
-          fsModuleCache: true,
         },
-      });
-    } finally {
-      if (originalRunnerOs === undefined) {
-        delete process.env.RUNNER_OS;
-      } else {
-        process.env.RUNNER_OS = originalRunnerOs;
-      }
-    }
+        "win32",
+      ),
+    ).toEqual({
+      experimental: {
+        fsModuleCache: true,
+      },
+    });
   });
 
   it("allows disabling the filesystem module cache explicitly", () => {
     expect(
-      loadVitestExperimentalConfig({
-        OPENCLAW_VITEST_FS_MODULE_CACHE: "0",
-      }),
+      loadVitestExperimentalConfig(
+        {
+          OPENCLAW_VITEST_FS_MODULE_CACHE: "0",
+        },
+        "linux",
+      ),
     ).toEqual({});
   });
 
   it("enables import timing output and import breakdown reporting", () => {
     expect(
-      loadVitestExperimentalConfig({
-        OPENCLAW_VITEST_IMPORT_DURATIONS: "true",
-        OPENCLAW_VITEST_PRINT_IMPORT_BREAKDOWN: "1",
-      }),
+      loadVitestExperimentalConfig(
+        {
+          OPENCLAW_VITEST_IMPORT_DURATIONS: "true",
+          OPENCLAW_VITEST_PRINT_IMPORT_BREAKDOWN: "1",
+        },
+        "linux",
+      ),
     ).toEqual({
       experimental: {
         fsModuleCache: true,
@@ -81,4 +72,8 @@ describe("loadVitestExperimentalConfig", () => {
       },
     });
   });
+
+  it("uses RUNNER_OS to detect Windows even when the platform is not win32", () => {
+    expect(loadVitestExperimentalConfig({ RUNNER_OS: "Windows" }, "linux")).toEqual({});
+  });
 });
diff --git a/vitest.performance-config.ts b/vitest.performance-config.ts
index a94e089b59..a03f7066a8 100644
--- a/vitest.performance-config.ts
+++ b/vitest.performance-config.ts
@@ -18,19 +18,24 @@ const isWindowsEnv = (env: EnvMap, platform: NodeJS.Platform): boolean => {
   return runnerOs === "windows";
 };
 
-export function loadVitestExperimentalConfig(env: EnvMap = process.env): {
+type VitestExperimentalConfig = {
   experimental?: {
     fsModuleCache?: true;
     importDurations?: { print: true };
     printImportBreakdown?: true;
   };
-} {
+};
+
+export function loadVitestExperimentalConfig(
+  env: EnvMap = process.env,
+  platform: NodeJS.Platform = process.platform,
+): VitestExperimentalConfig {
   const experimental: {
     fsModuleCache?: true;
     importDurations?: { print: true };
     printImportBreakdown?: true;
   } = {};
-  const windowsEnv = isWindowsEnv(env, process.platform);
+  const windowsEnv = isWindowsEnv(env, platform);
 
   if (!windowsEnv && !isDisabled(env.OPENCLAW_VITEST_FS_MODULE_CACHE)) {
     experimental.fsModuleCache = true;