fix(ui,i18n): E30 review round 3 — the stored language follows the screen, a fresh text starts collapsed, Retry waits again

frontend/src/components/BootGate.dom.test.tsx

@@ -8,7 +8,7 @@
 //
 // Real NavigationProvider, real storage and i18n; only the two boot probes are stubbed. The probe
 // records EVERY render, so "never showed the wrong page, not even for one render" is what is asserted.
-import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { describe, it, expect, vi, beforeEach, afterEach, type MockInstance } from "vitest";
 import { render, screen, cleanup, act, fireEvent, waitFor } from "@testing-library/react";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import { useEffect } from "react";
@@ -47,6 +47,7 @@ function mount() {
   return qc;
 }
 const account = (over: Partial<Me> = {}) => ({ id: 5, preferences: {}, ...over }) as Me;
+let savePrefs: MockInstance<typeof api.savePrefs>;
 const retryButton = () => screen.findByRole("button", { name: i18n.t("common.retry") });
 
 beforeEach(async () => {
@@ -57,6 +58,7 @@ beforeEach(async () => {
   mounts = 0;
   await i18n.changeLanguage("en");
   vi.spyOn(api, "setupStatus").mockResolvedValue({ configured: true });
+  savePrefs = vi.spyOn(api, "savePrefs").mockResolvedValue({ ok: true } as never);
 });
 afterEach(() => {
   cleanup();
@@ -85,6 +87,26 @@ describe("BootGate", () => {
     expect(renders.map((r) => r.lang)).toEqual(renders.map(() => "hu"));
   });
 
+  it("an account with no language stored stores the one it is shown in, once", async () => {
+    await i18n.changeLanguage("hu"); // the browser's language, never saved
+    vi.spyOn(api, "me").mockResolvedValue(account());
+    const qc = mount();
+
+    await screen.findByTestId("app");
+    await waitFor(() => expect(savePrefs).toHaveBeenCalledWith({ language: "hu" }));
+    expect(savePrefs).toHaveBeenCalledTimes(1);
+    // The server now sorts in Hungarian, and so does what reads the stored language.
+    await waitFor(() => expect(qc.getQueryData<Me>(qk.me())?.preferences.language).toBe("hu"));
+  });
+
+  it("an account with its language stored stores nothing", async () => {
+    vi.spyOn(api, "me").mockResolvedValue(account({ preferences: { language: "hu" } }));
+    mount();
+
+    await screen.findByTestId("app");
+    expect(savePrefs).not.toHaveBeenCalled();
+  });
+
   it("mounts nothing of the app while the identity is still unknown", async () => {
     vi.spyOn(api, "me").mockReturnValue(new Promise<Me | null>(() => {}));
     mount();