apps/web/android/app/src/main/AndroidManifest.xml

@@ -18,6 +18,17 @@
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
+            <!-- Custom scheme for the web app's "open the installed app"
+                 redirect (see apps/web/src/lib/mobile-app-redirect.ts) —
+                 additive, does not touch the launcher filter above. No
+                 android:host/android:path restriction, so any
+                 batchcooking://... URL matches. -->
+            <intent-filter>
+                <action android:name="android.intent.action.VIEW" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <category android:name="android.intent.category.BROWSABLE" />
+                <data android:scheme="batchcooking" />
+            </intent-filter>
         </activity>
 
         <provider

apps/web/cypress/component/mobile-app-redirect.cy.tsx

@@ -0,0 +1,98 @@
+import {
+  APP_OPEN_TIMEOUT_MS,
+  attemptOpenNativeApp,
+  isAndroidPhoneBrowser,
+  STAY_ON_WEB_PREFERENCE_KEY,
+} from "../../src/lib/mobile-app-redirect";
+
+// Pure-ish logic (timers/localStorage/document.hidden, no React component to
+// mount) — same posture as version-compare.cy.tsx: reuses the component-test
+// runner purely for `expect`/`cy.clock()`, no `cy.mount`. `.cy.tsx` (not
+// `.cy.ts`) only because that's what cypress.config.ts's component
+// `specPattern` looks for.
+
+function setUserAgent(ua: string) {
+  Object.defineProperty(window.navigator, "userAgent", { value: ua, configurable: true });
+}
+
+function setDocumentHidden(hidden: boolean) {
+  Object.defineProperty(document, "hidden", { value: hidden, configurable: true });
+}
+
+describe("isAndroidPhoneBrowser", () => {
+  afterEach(() => {
+    setUserAgent(window.navigator.userAgent);
+  });
+
+  it("is true for a real Android phone Chrome UA", () => {
+    setUserAgent(
+      "Mozilla/5.0 (Linux; Android 14; Pixel 7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0 Mobile Safari/537.36",
+    );
+    expect(isAndroidPhoneBrowser()).to.be.true;
+  });
+
+  it("is false for an Android tablet UA (Android without Mobile)", () => {
+    setUserAgent(
+      "Mozilla/5.0 (Linux; Android 14; SM-X200) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0 Safari/537.36",
+    );
+    expect(isAndroidPhoneBrowser()).to.be.false;
+  });
+
+  it("is false for a desktop UA", () => {
+    setUserAgent(
+      "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0 Safari/537.36",
+    );
+    expect(isAndroidPhoneBrowser()).to.be.false;
+  });
+});
+
+describe("attemptOpenNativeApp", () => {
+  beforeEach(() => {
+    localStorage.removeItem(STAY_ON_WEB_PREFERENCE_KEY);
+    setDocumentHidden(false);
+  });
+
+  afterEach(() => {
+    localStorage.removeItem(STAY_ON_WEB_PREFERENCE_KEY);
+    setDocumentHidden(false);
+  });
+
+  it("calls onFallback immediately, with no delay, when the visitor opted to stay on web", () => {
+    localStorage.setItem(STAY_ON_WEB_PREFERENCE_KEY, "true");
+    const onFallback = cy.stub().as("onFallback");
+
+    attemptOpenNativeApp({ onFallback });
+
+    cy.get("@onFallback").should("have.been.calledOnce");
+  });
+
+  it("calls onFallback once the delay elapses if the page never got hidden (app not installed)", () => {
+    cy.clock();
+    const onFallback = cy.stub().as("onFallback");
+
+    // `openAppUrl` stubbed to a no-op — real navigation to the custom
+    // scheme is only meaningful in a real browser with the app installed
+    // or not; here only the timer/visibility logic around it is under
+    // test (see the option's own doc comment in mobile-app-redirect.ts).
+    attemptOpenNativeApp({ onFallback, delayMs: APP_OPEN_TIMEOUT_MS, openAppUrl: () => {} });
+    cy.get("@onFallback").should("not.have.been.called");
+
+    cy.tick(APP_OPEN_TIMEOUT_MS);
+    cy.get("@onFallback").should("have.been.calledOnce");
+  });
+
+  it("never calls onFallback if the page is hidden before the delay elapses (handoff succeeded)", () => {
+    cy.clock();
+    const onFallback = cy.stub().as("onFallback");
+
+    attemptOpenNativeApp({ onFallback, delayMs: APP_OPEN_TIMEOUT_MS, openAppUrl: () => {} });
+
+    cy.then(() => {
+      setDocumentHidden(true);
+      document.dispatchEvent(new Event("visibilitychange"));
+    });
+
+    cy.tick(APP_OPEN_TIMEOUT_MS);
+    cy.get("@onFallback").should("not.have.been.called");
+  });
+});

apps/web/cypress/e2e/download-page.cy.ts

@@ -0,0 +1,26 @@
+// Pure layout spec, no Cucumber — a single static page with no user
+// journey of its own (see layout.cy.ts's identical rationale for this
+// 3-way test split). No `cy.intercept("**/auth/me", ...)` needed: this
+// route renders outside RequireAuth entirely (see App.tsx's own doc
+// comment on why), so it never calls that endpoint.
+
+describe("DownloadPage — the mobile-app-redirect fallback", () => {
+  it("renders the APK download link, a retry button, and a way back home", () => {
+    cy.visit("/telecharger");
+
+    cy.contains("h1", "Installer l'application Android").should("be.visible");
+
+    // API_BASE_URL is empty locally (relative-URL, same-origin default —
+    // see client.ts), so the real target collapses to this relative path.
+    cy.contains("a", "Télécharger l'APK").should("have.attr", "href", "/mobile/download");
+
+    cy.contains("button", "Réessayer d'ouvrir l'application").should("be.visible");
+
+    cy.contains("a", "Retour à l'accueil").should("have.attr", "href", "/");
+  });
+
+  it("is reachable without being logged in — no bounce to /login", () => {
+    cy.visit("/telecharger");
+    cy.url().should("include", "/telecharger");
+  });
+});

apps/web/src/App.tsx

@@ -14,6 +14,7 @@ import { ToursPage as AdminToursPage } from "./pages/admin/tours/ToursPage";
 import { LoginPage } from "./pages/auth/LoginPage";
 import { SignupPage } from "./pages/auth/SignupPage";
 import { CookingSessionPage } from "./pages/cooking-session/CookingSessionPage";
+import { DownloadPage } from "./pages/download/DownloadPage";
 import { OnboardingAllergensPage } from "./pages/onboarding/OnboardingAllergensPage";
 import { OnboardingDietPage } from "./pages/onboarding/OnboardingDietPage";
 import { OnboardingHouseholdPage } from "./pages/onboarding/OnboardingHouseholdPage";
@@ -53,6 +54,13 @@ import { ShoppingListPage } from "./pages/shopping-list/ShoppingListPage";
  * created/joined a household (see `OnboardingHouseholdPage`'s `goToNextStep`);
  * skipped otherwise, straight to `/onboarding/allergenes`.
  *
+ * `/telecharger` is the mobile-app-redirect chantier's fallback landing spot
+ * (see `lib/mobile-app-redirect.ts`'s own doc comment) — public like
+ * `/login`/`/signup`, but deliberately *not* wrapped in
+ * `RedirectIfAuthenticated`: a signed-in visitor still has a legitimate
+ * reason to land here (logged in on the web, app just not installed on
+ * this particular device yet).
+ *
  * `/admin/*` is the internal admin surface (metrics, monitoring, correction
  * triage, off-catalog ingredient review). It's its own top-level group,
  * wrapped in {@link AdminAuthProvider} so the `GET /admin/api/auth/me` session
@@ -140,6 +148,7 @@ export function App() {
           </RedirectIfAuthenticated>
         }
       />
+      <Route path="/telecharger" element={<DownloadPage />} />
       <Route
         element={
           <AdminAuthProvider>

apps/web/src/lib/mobile-app-redirect.ts

@@ -0,0 +1,107 @@
+/**
+ * The Android app's own custom URL scheme — registered as an *additional*,
+ * additive `<intent-filter>` in `android/app/src/main/AndroidManifest.xml`
+ * (the pre-existing `MAIN`/`LAUNCHER` filter is untouched). Attempting to
+ * navigate here from a browser hands off to the installed app; on a device
+ * without it installed, an unrecognized custom scheme is a safe no-op in
+ * every browser this app targets (Android Chrome/WebView) — the current
+ * page just keeps running, nothing throws, nothing navigates away.
+ */
+export const APP_OPEN_URL = "batchcooking://open";
+
+/**
+ * `localStorage` key for the "toujours ouvrir dans l'appli / rester sur le
+ * web" preference (UI for it lands in a later ticket of the mobile/tablet
+ * UI chantier, `/parametres/application`) — exported so that settings page
+ * can read/write the exact same key rather than this module and that page
+ * silently drifting to two different strings. Absent (the default) means
+ * "always try to open the app" — {@link attemptOpenNativeApp} never
+ * refuses to try just because nothing has set this yet.
+ */
+export const STAY_ON_WEB_PREFERENCE_KEY = "batchcooking:stayOnWeb";
+
+/** How long to wait for the OS to hand off to the app before assuming it isn't installed. Exported for tests, not meant to be tuned per call site. */
+export const APP_OPEN_TIMEOUT_MS = 1500;
+
+/**
+ * The "smart app banner" pattern: try to open the installed Android app via
+ * its custom scheme, and call `onFallback` if that doesn't visibly succeed
+ * within a short delay — the one signal available from a plain web page
+ * that a scheme navigation "worked" is that the OS backgrounds/replaces the
+ * tab (`document.hidden` flips `true`) to hand off to the other app; if the
+ * page is still the foreground document once the timer fires, nothing
+ * caught the scheme, so there's no app installed to open.
+ *
+ * Respects {@link STAY_ON_WEB_PREFERENCE_KEY}: when a visitor has
+ * explicitly asked to stay on the web, this skips the scheme attempt
+ * entirely and calls `onFallback` immediately — never a forced redirect a
+ * user has opted out of.
+ *
+ * `onFallback`'s job (typically: navigate to `/telecharger`) is entirely
+ * the caller's — this module has no opinion on routing.
+ */
+export function attemptOpenNativeApp({
+  onFallback,
+  delayMs = APP_OPEN_TIMEOUT_MS,
+  openAppUrl = navigateToAppScheme,
+}: {
+  onFallback: () => void;
+  /** Override for tests — production callers should always use the default. */
+  delayMs?: number;
+  /**
+   * Override for tests only — production callers should never pass this.
+   * Real navigation to an unrecognized custom scheme is a safe no-op in
+   * every browser this app targets, but it's still a real, uncontrolled
+   * side effect a test shouldn't actually trigger; every other behavior
+   * here (the timer, the visibility check, the preference short-circuit)
+   * is exercised the same way regardless of what this does.
+   */
+  openAppUrl?: () => void;
+}): void {
+  if (localStorage.getItem(STAY_ON_WEB_PREFERENCE_KEY) === "true") {
+    onFallback();
+    return;
+  }
+
+  const timeoutId = window.setTimeout(() => {
+    if (!document.hidden) onFallback();
+  }, delayMs);
+
+  // If the handoff actually happens, this tab is about to be backgrounded
+  // — clear the pending fallback the moment that's detected so it can
+  // never fire later (e.g. once the visitor switches back to this tab
+  // after using the app), and stop listening either way once it has fired
+  // once.
+  document.addEventListener("visibilitychange", handleVisibilityChange);
+
+  function handleVisibilityChange() {
+    if (!document.hidden) return;
+    window.clearTimeout(timeoutId);
+    document.removeEventListener("visibilitychange", handleVisibilityChange);
+  }
+
+  openAppUrl();
+}
+
+function navigateToAppScheme(): void {
+  window.location.href = APP_OPEN_URL;
+}
+
+/**
+ * Whether the current visitor is on an Android phone's browser — the one
+ * case {@link attemptOpenNativeApp} is worth trying at all, since the app
+ * only exists for Android (see the root README) and only in a phone form
+ * factor makes sense to redirect (a tablet browsing the site is a
+ * perfectly normal experience on its own, no app-open prompt needed).
+ *
+ * User-agent based, deliberately **not** {@link useIsMobileViewport} — that
+ * hook answers "is this viewport narrow" (a layout question, true for a
+ * resized desktop browser window too), this answers "is this genuinely an
+ * Android phone" (a capability question). Android's own UA convention
+ * drops "Mobile" from a *tablet's* UA string while keeping "Android" — the
+ * combination of both tokens is what actually narrows this to a phone.
+ */
+export function isAndroidPhoneBrowser(): boolean {
+  if (typeof navigator === "undefined") return false;
+  return /Android/.test(navigator.userAgent) && /Mobile/.test(navigator.userAgent);
+}

apps/web/src/locales/fr/translation.json

@@ -1365,6 +1365,13 @@
       "button": "Créer un compte"
     }
   },
+  "download": {
+    "title": "Installer l'application Android",
+    "lede": "Téléchargez le fichier .apk, ou réessayez d'ouvrir l'application si elle est déjà installée sur cet appareil.",
+    "downloadButton": "Télécharger l'APK",
+    "retryButton": "Réessayer d'ouvrir l'application",
+    "backLink": "Retour à l'accueil"
+  },
   "tour": {
     "controls": {
       "next": "Suivant",

apps/web/src/pages/download/DownloadPage.tsx

@@ -0,0 +1,54 @@
+import { useTranslation } from "react-i18next";
+import { Link } from "react-router-dom";
+import { API_BASE_URL } from "../../api/client";
+import { attemptOpenNativeApp } from "../../lib/mobile-app-redirect";
+import "./download-page.scss";
+
+/**
+ * The fallback landing spot for {@link attemptOpenNativeApp} — reached when
+ * a visitor's phone didn't have the app installed to hand off to (or,
+ * directly, by anyone who just wants the APK — a plain link works
+ * regardless of how they arrived). Public, no `RequireAuth`/
+ * `RedirectIfAuthenticated` gate: unlike `/login`/`/signup`, a signed-in
+ * visitor still has a legitimate reason to land here (they're logged in on
+ * the web but haven't installed the app on *this* device yet).
+ *
+ * The actual download reuses `${API_BASE_URL}/mobile/download` —
+ * `apps/api/src/modules/mobile/`'s existing same-origin proxy in front of
+ * Forgejo's release asset (see that module's own doc comment for why a
+ * direct Forgejo link doesn't work: no CORS headers, no GitHub-style
+ * `/releases/latest/download/<file>` shortcut). Nothing new needed there.
+ */
+export function DownloadPage() {
+  const { t } = useTranslation();
+
+  return (
+    <main className="download-page">
+      <div className="download-page__card">
+        <h1>{t("download.title")}</h1>
+        <p className="download-page__lede">{t("download.lede")}</p>
+
+        <a className="download-page__cta" href={`${API_BASE_URL}/mobile/download`}>
+          {t("download.downloadButton")}
+        </a>
+
+        <button
+          type="button"
+          className="download-page__retry"
+          // Already on the fallback page — a failed retry needs no further
+          // fallback of its own, the download button right above already
+          // covers it.
+          onClick={() => attemptOpenNativeApp({ onFallback: () => {} })}
+        >
+          {t("download.retryButton")}
+        </button>
+
+        <p className="download-page__hint">{t("landing.hero.mobileHint")}</p>
+
+        <Link className="download-page__back" to="/">
+          {t("download.backLink")}
+        </Link>
+      </div>
+    </main>
+  );
+}

apps/web/src/pages/download/download-page.scss

@@ -0,0 +1,84 @@
+// DownloadPage — colocated with DownloadPage.tsx. A small centered card,
+// same "full-viewport centering wrapper + raised card" language as
+// features/auth/auth-form.scss's `.auth-page`/`.auth-card` (this page sits
+// in the same "not logged in yet, or not on this device yet" context), but
+// its own classes rather than reused ones — no real behavior in common,
+// just a similar look.
+
+.download-page {
+  min-height: 100vh;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: var(--space-md);
+  background: var(--color-background);
+}
+
+.download-page__card {
+  display: flex;
+  flex-direction: column;
+  align-items: flex-start;
+  gap: var(--space-sm);
+  width: 100%;
+  max-width: var(--max-width-form);
+  padding: var(--space-xl);
+  background: var(--color-surface);
+  border-radius: var(--radius-md);
+  box-shadow: var(--shadow-md);
+  color: var(--color-text);
+
+  h1 {
+    font-size: var(--font-size-lg);
+    margin: 0;
+  }
+}
+
+.download-page__lede {
+  margin: 0;
+  color: var(--color-text-muted);
+}
+
+.download-page__cta {
+  align-self: stretch;
+  text-align: center;
+  padding: var(--space-sm) var(--space-md);
+  margin-top: var(--space-sm);
+  border-radius: var(--radius-base);
+  background: var(--color-primary);
+  color: #fff;
+  font-weight: 600;
+  text-decoration: none;
+
+  &:hover {
+    background: var(--color-primary-hover);
+  }
+}
+
+.download-page__retry {
+  align-self: stretch;
+  text-align: center;
+  padding: var(--space-sm) var(--space-md);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-base);
+  background: none;
+  color: var(--color-text);
+  font-family: var(--font-body);
+  font-weight: 600;
+  cursor: pointer;
+
+  &:hover {
+    background: var(--color-surface-alt);
+  }
+}
+
+.download-page__hint {
+  margin: 0;
+  font-size: var(--font-size-xs);
+  color: var(--color-text-muted);
+}
+
+.download-page__back {
+  margin-top: var(--space-sm);
+  font-size: var(--font-size-sm);
+  color: var(--color-primary);
+}