diff --git a/apps/web/src/app/layout.tsx b/apps/web/src/app/layout.tsx
index a40a92f..a4011f7 100644
--- a/apps/web/src/app/layout.tsx
+++ b/apps/web/src/app/layout.tsx
@@ -2,6 +2,7 @@ import type { Metadata } from 'next';
 import { NextIntlClientProvider } from 'next-intl';
 import { getLocale, getMessages } from 'next-intl/server';
 import { ThemeProvider } from 'next-themes';
+import { DesktopContextMenuGuard } from '@/components/desktop/desktop-context-menu-guard';
 import './globals.css';
 
 export const metadata: Metadata = {
@@ -27,6 +28,7 @@ export default async function RootLayout({
           disableTransitionOnChange
         >
           <NextIntlClientProvider messages={messages}>
+            <DesktopContextMenuGuard />
             {children}
           </NextIntlClientProvider>
         </ThemeProvider>
diff --git a/apps/web/src/components/desktop/desktop-context-menu-guard.test.tsx b/apps/web/src/components/desktop/desktop-context-menu-guard.test.tsx
new file mode 100644
index 0000000..29b86ee
--- /dev/null
+++ b/apps/web/src/components/desktop/desktop-context-menu-guard.test.tsx
@@ -0,0 +1,87 @@
+import { act, cleanup, render } from '@testing-library/react';
+import { afterEach, describe, expect, it } from 'vitest';
+import { DesktopContextMenuGuard } from './desktop-context-menu-guard';
+import { DESKTOP_COOKIE_NAME } from '@/lib/desktop-client';
+
+/**
+ * desktop-context-menu-guard.test (260917-h2s) — unterdrueckt das
+ * WebView2-Browser-Kontextmenue im Desktop-Client, laesst es in
+ * Eingabefeldern/contenteditable-Bereichen zu. `fire` gibt den
+ * `dispatchEvent`-Rueckgabewert zurueck: `false` bedeutet, `preventDefault()`
+ * wurde aufgerufen.
+ */
+function setCookie() {
+  document.cookie = `${DESKTOP_COOKIE_NAME}=1; path=/`;
+}
+
+function clearCookie() {
+  document.cookie = `${DESKTOP_COOKIE_NAME}=; expires=Thu, 01 Jan 1970 00:00:00 GMT; path=/`;
+}
+
+function fire(el: Element) {
+  return el.dispatchEvent(new MouseEvent('contextmenu', { bubbles: true, cancelable: true }));
+}
+
+afterEach(() => {
+  cleanup();
+  clearCookie();
+});
+
+describe('DesktopContextMenuGuard', () => {
+  it('mit Cookie: unterdrueckt ausserhalb von Eingabefeldern, laesst sie darin zu', async () => {
+    setCookie();
+    render(<DesktopContextMenuGuard />);
+    await act(async () => {});
+
+    const div = document.createElement('div');
+    document.body.appendChild(div);
+    expect(fire(div)).toBe(false);
+
+    const input = document.createElement('input');
+    document.body.appendChild(input);
+    expect(fire(input)).toBe(true);
+
+    const textarea = document.createElement('textarea');
+    document.body.appendChild(textarea);
+    expect(fire(textarea)).toBe(true);
+
+    const select = document.createElement('select');
+    document.body.appendChild(select);
+    expect(fire(select)).toBe(true);
+
+    const editable = document.createElement('div');
+    editable.setAttribute('contenteditable', 'true');
+    const span = document.createElement('span');
+    editable.appendChild(span);
+    document.body.appendChild(editable);
+    expect(fire(span)).toBe(true);
+
+    document.body.removeChild(div);
+    document.body.removeChild(input);
+    document.body.removeChild(textarea);
+    document.body.removeChild(select);
+    document.body.removeChild(editable);
+  });
+
+  it('ohne Cookie: Kontextmenue bleibt erlaubt', async () => {
+    render(<DesktopContextMenuGuard />);
+    await act(async () => {});
+
+    const div = document.createElement('div');
+    document.body.appendChild(div);
+    expect(fire(div)).toBe(true);
+    document.body.removeChild(div);
+  });
+
+  it('nach unmount: Kontextmenue bleibt wieder erlaubt', async () => {
+    setCookie();
+    const { unmount } = render(<DesktopContextMenuGuard />);
+    await act(async () => {});
+    unmount();
+
+    const div = document.createElement('div');
+    document.body.appendChild(div);
+    expect(fire(div)).toBe(true);
+    document.body.removeChild(div);
+  });
+});
diff --git a/apps/web/src/components/desktop/desktop-context-menu-guard.tsx b/apps/web/src/components/desktop/desktop-context-menu-guard.tsx
new file mode 100644
index 0000000..9c0bc99
--- /dev/null
+++ b/apps/web/src/components/desktop/desktop-context-menu-guard.tsx
@@ -0,0 +1,38 @@
+'use client';
+
+import { useEffect } from 'react';
+import { useIsDesktopClient } from '@/lib/desktop-client';
+
+/**
+ * DesktopContextMenuGuard (260917-h2s) — unterdrueckt das
+ * WebView2-Browser-Kontextmenue (Zurueck, Aktualisieren, Speichern unter,
+ * Drucken …) im Desktop-Client; in Eingabefeldern und contenteditable-
+ * Bereichen bleibt es erhalten, damit Kopieren/Einfuegen erreichbar bleibt.
+ * jsdom kennt `isContentEditable` nicht -- deshalb zusaetzlich der Selektor.
+ */
+const EDITABLE_SELECTOR =
+  'input, textarea, select, [contenteditable=""], [contenteditable="true"], [contenteditable="plaintext-only"]';
+
+export function DesktopContextMenuGuard() {
+  const isDesktop = useIsDesktopClient();
+
+  useEffect(() => {
+    if (!isDesktop) return;
+
+    const handler = (event: MouseEvent) => {
+      const target = event.target;
+      if (!(target instanceof Element)) return;
+      if (target.closest(EDITABLE_SELECTOR) || (target as HTMLElement).isContentEditable === true) {
+        return;
+      }
+      event.preventDefault();
+    };
+
+    document.addEventListener('contextmenu', handler);
+    return () => {
+      document.removeEventListener('contextmenu', handler);
+    };
+  }, [isDesktop]);
+
+  return null;
+}
diff --git a/apps/web/src/components/desktop/desktop-download-links.test.tsx b/apps/web/src/components/desktop/desktop-download-links.test.tsx
index 04365dd..759aeb5 100644
--- a/apps/web/src/components/desktop/desktop-download-links.test.tsx
+++ b/apps/web/src/components/desktop/desktop-download-links.test.tsx
@@ -1,4 +1,4 @@
-import { cleanup, render, screen } from '@testing-library/react';
+import { act, cleanup, render, screen } from '@testing-library/react';
 import { afterEach, describe, expect, it, vi } from 'vitest';
 import { DesktopDownloadLinks } from './desktop-download-links';
 
@@ -35,9 +35,14 @@ vi.mock('@/lib/desktop', async (importOriginal) => {
   };
 });
 
+function clearDesktopCookie() {
+  document.cookie = 'tessera_desktop=; expires=Thu, 01 Jan 1970 00:00:00 GMT; path=/';
+}
+
 afterEach(() => {
   cleanup();
   vi.clearAllMocks();
+  clearDesktopCookie();
 });
 
 const windowsFile = {
@@ -94,4 +99,19 @@ describe('DesktopDownloadLinks (18-03)', () => {
     expect(linuxLink.closest('a')).toHaveAttribute('href', 'http://localhost:3001/desktop/download/linux');
     expect(screen.queryByText('Linux-Version')).not.toBeInTheDocument();
   });
+
+  it('Test 4 (im Desktop-Client): rendert nichts und fragt /desktop/latest gar nicht erst an', async () => {
+    document.cookie = 'tessera_desktop=1; path=/';
+    loadDesktopLatest.mockResolvedValue({
+      version: '1.1.0',
+      channel: 'beta',
+      commit: 'abc1234',
+      buildTime: 'x',
+      files: { windows: windowsFile, linux: linuxFile },
+    });
+    const { container } = render(<DesktopDownloadLinks />);
+    await act(async () => {});
+    expect(loadDesktopLatest).not.toHaveBeenCalled();
+    expect(container.firstChild).toBeNull();
+  });
 });
diff --git a/apps/web/src/components/desktop/desktop-download-links.tsx b/apps/web/src/components/desktop/desktop-download-links.tsx
index 7464201..56cd892 100644
--- a/apps/web/src/components/desktop/desktop-download-links.tsx
+++ b/apps/web/src/components/desktop/desktop-download-links.tsx
@@ -3,18 +3,23 @@
 import { useEffect, useState } from 'react';
 import { useTranslations } from 'next-intl';
 import { desktopDownloadUrl, type DesktopLatestInfo, loadDesktopLatest } from '@/lib/desktop';
+import { isDesktopClient, useIsDesktopClient } from '@/lib/desktop-client';
 
 /**
  * Unauffaelliger Download-Link auf der Anmeldeseite (D-12): erscheint nur,
  * wenn `/desktop/latest` antwortet — kein Fehlertext, kein Ladeanzeiger,
  * nichts, solange nichts geladen ist. Windows fuehrt (Hauptlink), Linux
- * folgt als kleiner zweiter Link, wenn beide Pakete vorliegen.
+ * folgt als kleiner zweiter Link, wenn beide Pakete vorliegen. Im
+ * Desktop-Client entfaellt der Block komplett (260917-h2s) -- die Kennung
+ * kommt ueber das Cookie `tessera_desktop`.
  */
 export function DesktopDownloadLinks() {
   const t = useTranslations('auth');
   const [info, setInfo] = useState<DesktopLatestInfo | null>(null);
+  const isDesktop = useIsDesktopClient();
 
   useEffect(() => {
+    if (isDesktopClient()) return;
     let active = true;
     loadDesktopLatest().then((data) => {
       if (active) setInfo(data);
@@ -24,6 +29,10 @@ export function DesktopDownloadLinks() {
     };
   }, []);
 
+  if (isDesktop) {
+    return null;
+  }
+
   const files = info?.files;
   const windows = files?.windows;
   const linux = files?.linux;
diff --git a/apps/web/src/lib/desktop-client.test.ts b/apps/web/src/lib/desktop-client.test.ts
new file mode 100644
index 0000000..9486ac0
--- /dev/null
+++ b/apps/web/src/lib/desktop-client.test.ts
@@ -0,0 +1,52 @@
+import { act, renderHook, waitFor } from '@testing-library/react';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { DESKTOP_COOKIE_NAME, isDesktopClient, useIsDesktopClient } from './desktop-client';
+
+/**
+ * desktop-client.test — Gegenstueck zur Middleware (260917-h2s): liest das
+ * Cookie `tessera_desktop`, das die Middleware auf jede Antwort setzt, wenn
+ * der Desktop-Client `?desktop=1` an seine erste Navigation anhaengt.
+ */
+function clearCookie() {
+  document.cookie = `${DESKTOP_COOKIE_NAME}=; expires=Thu, 01 Jan 1970 00:00:00 GMT; path=/`;
+}
+
+afterEach(() => {
+  clearCookie();
+});
+
+describe('isDesktopClient', () => {
+  it('ohne Cookie: false', () => {
+    expect(isDesktopClient()).toBe(false);
+  });
+
+  it('mit tessera_desktop=1: true', () => {
+    document.cookie = `${DESKTOP_COOKIE_NAME}=1; path=/`;
+    expect(isDesktopClient()).toBe(true);
+  });
+
+  it('mit tessera_desktop=0: false', () => {
+    document.cookie = `${DESKTOP_COOKIE_NAME}=0; path=/`;
+    expect(isDesktopClient()).toBe(false);
+  });
+
+  it('ohne document: false', () => {
+    vi.stubGlobal('document', undefined);
+    expect(isDesktopClient()).toBe(false);
+    vi.unstubAllGlobals();
+  });
+});
+
+describe('useIsDesktopClient', () => {
+  it('Cookie gesetzt: liefert nach dem Effekt true', async () => {
+    document.cookie = `${DESKTOP_COOKIE_NAME}=1; path=/`;
+    const { result } = renderHook(() => useIsDesktopClient());
+    await waitFor(() => expect(result.current).toBe(true));
+  });
+
+  it('ohne Cookie: bleibt false', async () => {
+    const { result } = renderHook(() => useIsDesktopClient());
+    await act(async () => {});
+    expect(result.current).toBe(false);
+  });
+});
diff --git a/apps/web/src/lib/desktop-client.ts b/apps/web/src/lib/desktop-client.ts
new file mode 100644
index 0000000..5860aac
--- /dev/null
+++ b/apps/web/src/lib/desktop-client.ts
@@ -0,0 +1,34 @@
+import { useEffect, useState } from 'react';
+
+/**
+ * desktop-client — erkennt, ob die Seite im Desktop-Client laeuft
+ * (260917-h2s). Gegenstueck zur Middleware (apps/web/src/middleware.ts,
+ * `withDesktopCookie`): der Rust-Client haengt `desktop=1` an seine erste
+ * Navigation, die Middleware setzt daraufhin das Cookie `tessera_desktop`
+ * auf jede Antwort. `isDesktopClient()` liest das Cookie synchron.
+ */
+export const DESKTOP_COOKIE_NAME = 'tessera_desktop';
+
+export function isDesktopClient(): boolean {
+  if (typeof document === 'undefined') {
+    return false;
+  }
+  return document.cookie
+    .split(';')
+    .some((c) => c.trim() === `${DESKTOP_COOKIE_NAME}=1`);
+}
+
+/**
+ * Hook statt direktem Aufruf beim Render: `isDesktopClient()` synchron im
+ * ersten Render zu nutzen wuerde Server-HTML (kein `document`) und den
+ * ersten Client-Render auseinanderlaufen lassen -- Hydration-Fehler. Der
+ * `useEffect` gleicht das an; `useState(false)` haelt Server- und
+ * Erst-Render-Ergebnis identisch.
+ */
+export function useIsDesktopClient(): boolean {
+  const [isDesktop, setIsDesktop] = useState(false);
+  useEffect(() => {
+    setIsDesktop(isDesktopClient());
+  }, []);
+  return isDesktop;
+}
diff --git a/apps/web/src/middleware.test.ts b/apps/web/src/middleware.test.ts
new file mode 100644
index 0000000..901e1b9
--- /dev/null
+++ b/apps/web/src/middleware.test.ts
@@ -0,0 +1,68 @@
+// @vitest-environment node
+import { NextRequest } from 'next/server';
+import { SignJWT } from 'jose';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { middleware } from './middleware';
+
+/**
+ * middleware.test — Desktop-Client-Cookie (260917-h2s), eigener describe-Block
+ * neben den bestehenden Redirect-/Session-Faellen. `@vitest-environment node`,
+ * weil `NextRequest`/`NextResponse` node-typische APIs (Headers, URL) nutzen,
+ * die im jsdom-Standardmilieu der Suite nicht gebraucht werden.
+ */
+describe('middleware — Desktop-Client-Cookie (260917-h2s)', () => {
+  beforeEach(() => {
+    vi.stubEnv('JWT_SECRET', 'test-secret');
+  });
+
+  afterEach(() => {
+    vi.unstubAllEnvs();
+  });
+
+  it('Test 1: /login?desktop=1 setzt das Cookie tessera_desktop=1', async () => {
+    const req = new NextRequest('http://localhost:3000/login?desktop=1');
+    const res = await middleware(req);
+    const setCookie = res.headers.get('set-cookie');
+    expect(setCookie).toContain('tessera_desktop=1');
+    expect(setCookie).toContain('Path=/');
+    expect(setCookie).toContain('Max-Age=31536000');
+    expect(setCookie).toContain('SameSite=lax');
+    expect(setCookie).not.toContain('Secure');
+    expect(setCookie).not.toContain('HttpOnly');
+  });
+
+  it('Test 2: /login ohne Parameter setzt kein Cookie', async () => {
+    const req = new NextRequest('http://localhost:3000/login');
+    const res = await middleware(req);
+    expect(res.headers.get('set-cookie')).toBeNull();
+  });
+
+  it('Test 3: /dashboard?desktop=1 ohne Session leitet um und setzt das Cookie', async () => {
+    const req = new NextRequest('http://localhost:3000/dashboard?desktop=1');
+    const res = await middleware(req);
+    expect(res.status).toBe(307);
+    expect(res.headers.get('location')).toContain('/login');
+    expect(res.headers.get('set-cookie')).toContain('tessera_desktop=1');
+  });
+
+  it('Test 4: https setzt Secure', async () => {
+    const req = new NextRequest('https://tessera.example.com/login?desktop=1');
+    const res = await middleware(req);
+    expect(res.headers.get('set-cookie')).toContain('Secure');
+  });
+
+  it('Test 5: gueltiges JWT laesst die Anfrage durch und setzt trotzdem das Cookie', async () => {
+    const token = await new SignJWT({ sub: 'u1' })
+      .setProtectedHeader({ alg: 'HS256' })
+      .setIssuedAt()
+      .setExpirationTime('5m')
+      .sign(new TextEncoder().encode('test-secret'));
+
+    const req = new NextRequest('http://localhost:3000/dashboard?desktop=1', {
+      headers: { cookie: `session=${token}` },
+    });
+    const res = await middleware(req);
+    expect(res.headers.get('set-cookie')).toContain('tessera_desktop=1');
+    expect(res.headers.get('x-middleware-next')).toBe('1');
+  });
+});
diff --git a/apps/web/src/middleware.ts b/apps/web/src/middleware.ts
index 5a55670..dc6e7ad 100644
--- a/apps/web/src/middleware.ts
+++ b/apps/web/src/middleware.ts
@@ -12,6 +12,31 @@ import { buildNextParam } from '@/lib/safe-next';
 
 const publicRoutes = ['/login', '/reset-password'];
 
+const DESKTOP_COOKIE = 'tessera_desktop';
+
+/**
+ * Setzt das Cookie `tessera_desktop`, wenn die Anfrage `?desktop=1` traegt
+ * (260917-h2s). Der Desktop-Client (apps/desktop/src-tauri/src/lib.rs,
+ * `with_desktop_marker`) haengt den Parameter nur an seine ERSTE Navigation
+ * an; das Cookie muss deshalb auf JEDER Antwort landen, auch auf dem
+ * Fruehausstieg fuer oeffentliche Routen und auf Redirects -- sonst geht die
+ * Kennung beim 307 nach /login verloren. `httpOnly: false` ist Absicht (wird
+ * von `isDesktopClient()` in apps/web/src/lib/desktop-client.ts gelesen);
+ * der Wert ist kein Geheimnis.
+ */
+function withDesktopCookie(req: NextRequest, res: NextResponse): NextResponse {
+  if (req.nextUrl.searchParams.get('desktop') === '1') {
+    res.cookies.set(DESKTOP_COOKIE, '1', {
+      path: '/',
+      maxAge: 60 * 60 * 24 * 365,
+      sameSite: 'lax',
+      httpOnly: false,
+      secure: req.nextUrl.protocol === 'https:',
+    });
+  }
+  return res;
+}
+
 /**
  * Umleitung zur Anmeldeseite mit `next`-Parameter (quick-260917-gyd): Pfad
  * + Query der urspruenglich angeforderten Seite wandern mit, damit die
@@ -42,7 +67,7 @@ export async function middleware(req: NextRequest) {
 
   // Allow public routes without authentication
   if (publicRoutes.some((route) => path.startsWith(route))) {
-    return NextResponse.next();
+    return withDesktopCookie(req, NextResponse.next());
   }
 
   // Skip static assets and API routes (handled by NestJS)
@@ -52,14 +77,14 @@ export async function middleware(req: NextRequest) {
     path.startsWith('/favicon.ico') ||
     path.startsWith('/api')
   ) {
-    return NextResponse.next();
+    return withDesktopCookie(req, NextResponse.next());
   }
 
   // Read session cookie
   const session = req.cookies.get('session')?.value;
 
   if (!session) {
-    return redirectToLogin(req);
+    return withDesktopCookie(req, redirectToLogin(req));
   }
 
   try {
@@ -72,15 +97,18 @@ export async function middleware(req: NextRequest) {
       payload.mustChangePassword === true &&
       !path.startsWith('/change-password')
     ) {
-      return NextResponse.redirect(new URL('/change-password', req.nextUrl));
+      return withDesktopCookie(
+        req,
+        NextResponse.redirect(new URL('/change-password', req.nextUrl)),
+      );
     }
 
-    return NextResponse.next();
+    return withDesktopCookie(req, NextResponse.next());
   } catch {
     // JWT verification failed -- clear stale cookie and redirect to login
     const response = redirectToLogin(req);
     response.cookies.delete('session');
-    return response;
+    return withDesktopCookie(req, response);
   }
 }