test(frontend): MSW server + renderWithProviders harness

frontend/src/test-setup.ts

@@ -1 +1,7 @@
 import "@testing-library/jest-dom/vitest";
+import { afterAll, afterEach, beforeAll } from "vitest";
+import { mswServer } from "./testing/msw";
+
+beforeAll(() => mswServer.listen({ onUnhandledRequest: "error" }));
+afterEach(() => mswServer.resetHandlers());
+afterAll(() => mswServer.close());

frontend/src/testing/msw.ts

@@ -0,0 +1,12 @@
+import { setupServer } from "msw/node";
+import { http, HttpResponse } from "msw";
+
+// Component tests override these per case with `server.use(...)`.
+// Defaults simulate "logged out" so any suite that forgets to override gets a
+// clear signal instead of silent 200s.
+const defaultHandlers = [
+  http.get("/api/session/me", () => new HttpResponse(null, { status: 401 })),
+];
+
+export const mswServer = setupServer(...defaultHandlers);
+export { http, HttpResponse };

frontend/src/testing/renderWithProviders.tsx

@@ -0,0 +1,26 @@
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { render, type RenderOptions, type RenderResult } from "@testing-library/react";
+import { MemoryRouter, type MemoryRouterProps } from "react-router-dom";
+import type { PropsWithChildren, ReactElement } from "react";
+
+interface Options extends Omit<RenderOptions, "wrapper"> {
+  route?: string;
+  routerProps?: MemoryRouterProps;
+}
+
+export function renderWithProviders(ui: ReactElement, opts: Options = {}): RenderResult & { queryClient: QueryClient } {
+  const queryClient = new QueryClient({
+    defaultOptions: {
+      queries: { retry: false, gcTime: 0, staleTime: 0 },
+      mutations: { retry: false },
+    },
+  });
+  const Wrapper = ({ children }: PropsWithChildren) => (
+    <QueryClientProvider client={queryClient}>
+      <MemoryRouter initialEntries={[opts.route ?? "/"]} {...opts.routerProps}>
+        {children}
+      </MemoryRouter>
+    </QueryClientProvider>
+  );
+  return { ...render(ui, { ...opts, wrapper: Wrapper }), queryClient };
+}