Replace short-lived no-mobile-guide-redirect cookie with SessionStorage (#34350)

* Replace short-lived no-mobile-guide-redirect cookie with SessionStorage

* Add coverage

apps/web/src/toasts/MobileGuideToast.test.ts

@@ -0,0 +1,41 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+// @vitest-environment happy-dom
+// @vitest-environment-options {"settings": {"navigator": {"userAgent": "Mozilla/5.0 (iPod touch; CPU iPhone OS 8_4_1 like Mac OS X) AppleWebKit/600.1.4 (KHTML, like Gecko) Version/8.0 Mobile/12H321 Safari/600.1.4" }}}
+
+import { type ComponentProps } from "react";
+import { vi, describe, it, expect, beforeEach } from "vitest";
+
+import ToastStore from "../stores/ToastStore.ts";
+import { showToast } from "./MobileGuideToast.ts";
+import type GenericToast from "../components/views/toasts/GenericToast.tsx";
+
+describe("showToast", () => {
+    const addOrReplaceToastSpy = vi.spyOn(ToastStore.sharedInstance(), "addOrReplaceToast");
+
+    beforeEach(() => {
+        sessionStorage.clear();
+    });
+
+    it("should do nothing if sessionStorage has `skip_mobile_redirect`", () => {
+        sessionStorage.setItem("skip_mobile_redirect", "true");
+
+        showToast();
+        expect(addOrReplaceToastSpy).not.toHaveBeenCalled();
+    });
+
+    it("should set sessionStorage `skip_mobile_redirect` on reject", () => {
+        expect(sessionStorage.getItem("skip_mobile_redirect")).toBeFalsy();
+
+        showToast();
+        const toast = addOrReplaceToastSpy.mock.calls[0][0];
+        expect((toast.props as ComponentProps<typeof GenericToast>).secondaryLabel).toBe("Dismiss");
+        (toast.props as ComponentProps<typeof GenericToast>).onSecondaryClick!();
+        expect(sessionStorage.getItem("skip_mobile_redirect")).toBe("true");
+    });
+});

apps/web/src/toasts/MobileGuideToast.ts

@@ -16,7 +16,7 @@ const onAccept = (): void => {
 };
 
 const onReject = (): void => {
-    document.cookie = "element_mobile_redirect_to_guide=false;path=/;max-age=14400";
+    sessionStorage.setItem("skip_mobile_redirect", "true");
     hideToast();
 };
 
@@ -29,7 +29,7 @@ export const showToast = (): void => {
     if (!isIos && !isAndroid) {
         return;
     }
-    if (document.cookie.includes("element_mobile_redirect_to_guide=false")) {
+    if (sessionStorage.getItem("skip_mobile_redirect") === "true") {
         return;
     }
     ToastStore.sharedInstance().addOrReplaceToast({

apps/web/src/vector/index.ts

@@ -150,7 +150,7 @@ async function start(): Promise<void> {
             const isIos = /iPad|iPhone|iPod/.test(navigator.userAgent) && !window.MSStream;
             const isAndroid = /Android/.test(navigator.userAgent);
             if (isIos || isAndroid) {
-                if (document.cookie.indexOf("element_mobile_redirect_to_guide=false") === -1) {
+                if (sessionStorage.getItem("skip_mobile_redirect") !== "true") {
                     window.location.href = "mobile_guide/";
                     return;
                 }

apps/web/src/vector/mobile_guide/index.test.ts

@@ -0,0 +1,45 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+// @vitest-environment happy-dom
+
+import { vi, describe, it, expect, beforeEach, beforeAll } from "vitest";
+import { waitFor } from "@testing-library/dom";
+import fetchMock from "@fetch-mock/vitest";
+
+vi.mock("../getconfig.ts", () => ({
+    getVectorConfig: vi.fn().mockResolvedValue({ default_server_name: "server_name" }),
+}));
+vi.mock("./mobile-apps.ts");
+
+describe("onBackToElementClick", () => {
+    beforeAll(async () => {
+        const backButton = document.createElement("a");
+        backButton.id = "back_to_element_button";
+        backButton.textContent = "Back";
+        document.body.append(backButton);
+
+        fetchMock.get("https://server_name/.well-known/matrix/client", {
+            "m.homeserver": {
+                base_url: "https://server/",
+            },
+        });
+        await import("./index.ts");
+    });
+
+    beforeEach(async () => {
+        sessionStorage.clear();
+    });
+
+    it("should set skip_mobile_redirect in sessionStorage", async () => {
+        expect(sessionStorage.getItem("skip_mobile_redirect")).toBeFalsy();
+        const button = document.getElementById("back_to_element_button")!;
+        await waitFor(() => expect(button.onclick).toBeTruthy());
+        button.click();
+        expect(sessionStorage.getItem("skip_mobile_redirect")).toBe("true");
+    });
+});

apps/web/src/vector/mobile_guide/index.ts

@@ -15,8 +15,7 @@ import { getVectorConfig } from "../getconfig";
 import { MobileAppVariant, mobileApps, updateMobilePage } from "./mobile-apps.ts";
 
 function onBackToElementClick(): void {
-    // Cookie should expire in 4 hours
-    document.cookie = "element_mobile_redirect_to_guide=false;path=/;max-age=14400";
+    sessionStorage.setItem("skip_mobile_redirect", "true");
     window.location.href = "../";
 }