Fix landing locale toggle cache path

frontend/app/page.tsx

@@ -1,6 +1,7 @@
 import type { Metadata } from "next";
 import { redirect } from "next/navigation";
 import { InstitutionalLandingPage } from "@/components/landing/InstitutionalLandingPage";
+import { LANDING_LOCALE_QUERY_PARAM } from "@/components/landing/landingLocale";
 
 export const metadata: Metadata = {
   title: "PolyWeather | Institutional Weather Signal Intelligence",
@@ -32,6 +33,8 @@ export default async function HomePage({
     const qs = usp.toString();
     redirect(`/auth/callback${qs ? `?${qs}` : ""}`);
   }
+  const rawLandingLocale = params[LANDING_LOCALE_QUERY_PARAM];
+  const landingLocale = Array.isArray(rawLandingLocale) ? rawLandingLocale[0] : rawLandingLocale;
   const jsonLd = {
     "@context": "https://schema.org",
     "@type": "WebApplication",
@@ -68,7 +71,7 @@ export default async function HomePage({
         type="application/ld+json"
         dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
       />
-      <InstitutionalLandingPage />
+      <InstitutionalLandingPage queryLocale={landingLocale} />
     </>
   );
 }

frontend/components/landing/InstitutionalLandingPage.tsx

@@ -227,9 +227,10 @@ function WeatherWorkflowIllustration() {
   );
 }
 
-async function resolveLandingLocale(): Promise<LandingLocale> {
+async function resolveLandingLocale(queryLocale?: string | null): Promise<LandingLocale> {
   const [cookieStore, headerStore] = await Promise.all([cookies(), headers()]);
   return pickLandingLocale(
+    queryLocale,
     cookieStore.get(LANDING_LOCALE_COOKIE)?.value,
     headerStore.get("accept-language"),
   );
@@ -829,7 +830,11 @@ function InstitutionalLandingScreen({ locale }: { locale: LandingLocale }) {
   );
 }
 
-export async function InstitutionalLandingPage() {
-  const locale = await resolveLandingLocale();
+export async function InstitutionalLandingPage({
+  queryLocale,
+}: {
+  queryLocale?: string | null;
+} = {}) {
+  const locale = await resolveLandingLocale(queryLocale);
   return <InstitutionalLandingScreen locale={locale} />;
 }

frontend/components/landing/LandingLocaleToggle.tsx

@@ -1,9 +1,8 @@
 "use client";
 
-import { useTransition } from "react";
-import { useRouter } from "next/navigation";
 import {
   LANDING_LOCALE_COOKIE,
+  LANDING_LOCALE_QUERY_PARAM,
   nextLandingLocale,
   type LandingLocale,
 } from "@/components/landing/landingLocale";
@@ -11,8 +10,6 @@ import {
 const ONE_YEAR_SECONDS = 60 * 60 * 24 * 365;
 
 export function LandingLocaleToggle({ locale }: { locale: LandingLocale }) {
-  const router = useRouter();
-  const [isPending, startTransition] = useTransition();
   const isEn = locale === "en-US";
 
   const toggleLocale = () => {
@@ -24,16 +21,16 @@ export function LandingLocaleToggle({ locale }: { locale: LandingLocale }) {
     } catch {
       // Locale persistence is best-effort; the cookie is enough for SSR.
     }
-    startTransition(() => {
-      router.refresh();
-    });
+
+    const url = new URL(window.location.href);
+    url.searchParams.set(LANDING_LOCALE_QUERY_PARAM, nextLocale);
+    window.location.assign(url.toString());
   };
 
   return (
     <button
       type="button"
       onClick={toggleLocale}
-      disabled={isPending}
       className="inline-flex h-9 cursor-pointer items-center gap-1 rounded-md border border-slate-200 bg-white px-1 text-xs font-semibold text-slate-500 shadow-sm hover:border-slate-300 disabled:cursor-wait disabled:opacity-70"
       aria-label={isEn ? "Switch language" : "切换语言"}
     >

frontend/components/landing/__tests__/landingPricingReferral.test.ts

@@ -23,6 +23,10 @@ export function runTests() {
     path.join(root, "components", "landing", "LandingLocaleToggle.tsx"),
     "utf8",
   );
+  const localeHelperSource = fs.readFileSync(
+    path.join(root, "components", "landing", "landingLocale.ts"),
+    "utf8",
+  );
   const staticCitiesSource = fs.readFileSync(
     path.join(root, "lib", "static-cities.ts"),
     "utf8",
@@ -48,6 +52,18 @@ export function runTests() {
   assert(!authActionsSource.includes("lucide-react"), "auth island must avoid shipping lucide-react");
   assert(!localeToggleSource.includes("lucide-react"), "locale island must avoid shipping lucide-react");
   assert(!analyticsSource.includes("lucide-react"), "analytics island must avoid shipping lucide-react");
+  assert(
+    localeToggleSource.includes("new URL(window.location.href)") &&
+      localeToggleSource.includes("LANDING_LOCALE_QUERY_PARAM") &&
+      localeToggleSource.includes("window.location.assign(url.toString())"),
+    "landing locale toggle must navigate with an explicit locale query so CDN-cached HTML cannot ignore cookie-only changes",
+  );
+  assert(
+    localeHelperSource.includes("queryLocale") &&
+      source.includes("resolveLandingLocale(queryLocale") &&
+      appPageSource.includes("<InstitutionalLandingPage queryLocale={landingLocale} />"),
+    "landing route must prefer an explicit locale query before cookie or Accept-Language",
+  );
   assert(source.includes("3 天免费试用"), "landing page must advertise the 3-day trial");
   assert(source.includes("试用期权益和 Pro 一致，除了不显示付费 Telegram 群链接"), "landing page must state trial access matches Pro except the paid group link");
   assert(!source.includes("高频刷新与 API 仍为 Pro 权益"), "landing page must not incorrectly exclude high-frequency refresh or API from trial access");

frontend/components/landing/landingLocale.ts

@@ -1,6 +1,7 @@
 export type LandingLocale = "zh-CN" | "en-US";
 
 export const LANDING_LOCALE_COOKIE = "polyweather.locale";
+export const LANDING_LOCALE_QUERY_PARAM = "locale";
 export const DEFAULT_LANDING_LOCALE: LandingLocale = "zh-CN";
 
 export function normalizeLandingLocale(value: string | null | undefined): LandingLocale | null {
@@ -16,9 +17,13 @@ export function normalizeLandingLocale(value: string | null | undefined): Landin
 }
 
 export function pickLandingLocale(
+  queryLocale: string | null | undefined,
   cookieLocale: string | null | undefined,
   acceptLanguage: string | null | undefined,
 ): LandingLocale {
+  const fromQuery = normalizeLandingLocale(queryLocale);
+  if (fromQuery) return fromQuery;
+
   const fromCookie = normalizeLandingLocale(cookieLocale);
   if (fromCookie) return fromCookie;