diff --git a/src/test/setup.ts b/src/test/setup.ts
index 97877956..f2b26ff5 100644
--- a/src/test/setup.ts
+++ b/src/test/setup.ts
@@ -1,11 +1,44 @@
 import "@testing-library/jest-dom/vitest";
 import { cleanup } from "@testing-library/react";
-import { afterEach } from "vitest";
+import { afterEach, vi } from "vitest";
 
 afterEach(() => {
   cleanup();
 });
 
+function localStorageIsUsable(): boolean {
+  try {
+    const probe = "__vitest_ls_probe__";
+    globalThis.localStorage.setItem(probe, "1");
+    const ok = globalThis.localStorage.getItem(probe) === "1";
+    globalThis.localStorage.removeItem(probe);
+    return ok;
+  } catch {
+    return false;
+  }
+}
+
+// Node 25+ / some harnesses lack a stable localStorage — provide an in-memory mock when needed.
+if (!localStorageIsUsable()) {
+  const store = new Map<string, string>();
+  vi.stubGlobal("localStorage", {
+    getItem: (key: string) => store.get(key) ?? null,
+    setItem: (key: string, value: string) => {
+      store.set(key, String(value));
+    },
+    removeItem: (key: string) => {
+      store.delete(key);
+    },
+    clear: () => {
+      store.clear();
+    },
+    get length() {
+      return store.size;
+    },
+    key: (index: number) => [...store.keys()][index] ?? null,
+  });
+}
+
 Object.defineProperty(window, "matchMedia", {
   writable: true,
   value: (query: string) => ({