feat(ui): force Mini App fullscreen on mobile, not via the share link

Replace the shared-link &mode=fullscreen (which would also force fullscreen on
desktop) with an imperative requestFullscreen() on launch, gated to mobile
clients (ios/android/android_x) — mirroring how Telegram's own Mini Apps go
immersive on phones while desktop keeps the bot's full-size window. It triggers
the existing fullscreenChanged -> safe-area resync; a no-op on clients predating
Bot API 8.0.

ui/src/lib/app.svelte.ts

@@ -19,6 +19,7 @@ import {
   telegramHaptic,
   telegramLaunch,
   telegramOnEvent,
+  telegramRequestFullscreen,
   telegramSetChrome,
 } from './telegram';
 import { parseStartParam } from './deeplink';
@@ -463,6 +464,10 @@ export async function bootstrap(): Promise<void> {
     telegramOnEvent('safeAreaChanged', syncTelegramSafeArea);
     telegramOnEvent('fullscreenChanged', syncTelegramSafeArea);
     telegramDisableVerticalSwipes();
+    // On mobile, go immersive fullscreen like Telegram's own Mini Apps; the fullscreenChanged
+    // listener above then re-syncs the safe-area insets. Desktop keeps the bot's full-size
+    // window. No-op on clients predating Bot API 8.0.
+    telegramRequestFullscreen();
     try {
       await adoptSession(await gateway.authTelegram(launch.initData));
       // A blocked account skips deep-link routing — the blocked screen overlays every route.

ui/src/lib/deeplink.test.ts

@@ -33,20 +33,20 @@ describe('shareLink', () => {
 
   it('wraps a payload in a startapp link', () => {
     vi.stubEnv('VITE_TELEGRAM_LINK', 'https://t.me/bot/app');
-    expect(shareLink('f123456')).toBe('https://t.me/bot/app?startapp=f123456&mode=fullscreen');
+    expect(shareLink('f123456')).toBe('https://t.me/bot/app?startapp=f123456');
   });
 
   it('picks the per-bot base by language', () => {
     vi.stubEnv('VITE_TELEGRAM_LINK_EN', 'https://t.me/enbot/app');
     vi.stubEnv('VITE_TELEGRAM_LINK_RU', 'https://t.me/rubot/app');
-    expect(shareLink('f1', 'en')).toBe('https://t.me/enbot/app?startapp=f1&mode=fullscreen');
-    expect(shareLink('f1', 'ru')).toBe('https://t.me/rubot/app?startapp=f1&mode=fullscreen');
+    expect(shareLink('f1', 'en')).toBe('https://t.me/enbot/app?startapp=f1');
+    expect(shareLink('f1', 'ru')).toBe('https://t.me/rubot/app?startapp=f1');
   });
 
   it('falls back to the language-agnostic base when the per-bot one is unset', () => {
     vi.stubEnv('VITE_TELEGRAM_LINK', 'https://t.me/fallback/app');
     vi.stubEnv('VITE_TELEGRAM_LINK_RU', '');
-    expect(shareLink('f1', 'ru')).toBe('https://t.me/fallback/app?startapp=f1&mode=fullscreen');
+    expect(shareLink('f1', 'ru')).toBe('https://t.me/fallback/app?startapp=f1');
   });
 });
 

ui/src/lib/deeplink.ts

@@ -78,7 +78,5 @@ export function shareLink(param: string, lang = ''): string | null {
   const base = telegramBase(lang);
   if (!base) return null;
   const sep = base.includes('?') ? '&' : '?';
-  // mode=fullscreen opens the Mini App fullscreen, matching how the bot's own entry
-  // opens it, so a shared link and the bot give the same experience.
-  return `${base}${sep}startapp=${encodeURIComponent(param)}&mode=fullscreen`;
+  return `${base}${sep}startapp=${encodeURIComponent(param)}`;
 }

ui/src/lib/telegram.test.ts

@@ -1,5 +1,5 @@
 import { afterEach, describe, expect, it, vi } from 'vitest';
-import { insideTelegram, telegramClosingConfirmation, telegramLaunch } from './telegram';
+import { insideTelegram, telegramClosingConfirmation, telegramLaunch, telegramRequestFullscreen } from './telegram';
 
 function stubWebApp(initData: string, startParam?: string) {
   vi.stubGlobal('window', {
@@ -38,22 +38,28 @@ describe('telegram launch detection', () => {
   });
 });
 
+// stubClient stands up a fake WebApp on the given platform with spies for the mobile-gated
+// chrome toggles, so the platform gate can be asserted without a real Telegram client.
+function stubClient(platform?: string) {
+  const enable = vi.fn();
+  const disable = vi.fn();
+  const requestFullscreen = vi.fn();
+  vi.stubGlobal('window', {
+    Telegram: {
+      WebApp: { platform, enableClosingConfirmation: enable, disableClosingConfirmation: disable, requestFullscreen },
+    },
+  });
+  return { enable, disable, requestFullscreen };
+}
+
+const mobilePlatforms = ['ios', 'android', 'android_x'];
+const desktopPlatforms = ['tdesktop', 'macos', 'web', undefined];
+
 describe('telegramClosingConfirmation', () => {
   afterEach(() => vi.unstubAllGlobals());
 
-  // stubClient stands up a fake WebApp on the given platform with spies for the close-guard
-  // toggles, so the platform gate can be asserted without a real Telegram client.
-  function stubClient(platform?: string) {
-    const enable = vi.fn();
-    const disable = vi.fn();
-    vi.stubGlobal('window', {
-      Telegram: { WebApp: { platform, enableClosingConfirmation: enable, disableClosingConfirmation: disable } },
-    });
-    return { enable, disable };
-  }
-
   it('arms the close guard on mobile clients', () => {
-    for (const p of ['ios', 'android']) {
+    for (const p of mobilePlatforms) {
       const { enable } = stubClient(p);
       telegramClosingConfirmation(true);
       expect(enable, `platform=${p}`).toHaveBeenCalledOnce();
@@ -61,7 +67,7 @@ describe('telegramClosingConfirmation', () => {
   });
 
   it('skips the close guard on desktop clients (the dialog there is just noise)', () => {
-    for (const p of ['tdesktop', 'macos', 'web', undefined]) {
+    for (const p of desktopPlatforms) {
       const { enable } = stubClient(p);
       telegramClosingConfirmation(true);
       expect(enable, `platform=${p}`).not.toHaveBeenCalled();
@@ -74,3 +80,23 @@ describe('telegramClosingConfirmation', () => {
     expect(disable).toHaveBeenCalledOnce();
   });
 });
+
+describe('telegramRequestFullscreen', () => {
+  afterEach(() => vi.unstubAllGlobals());
+
+  it('goes immersive fullscreen on mobile clients', () => {
+    for (const p of mobilePlatforms) {
+      const { requestFullscreen } = stubClient(p);
+      telegramRequestFullscreen();
+      expect(requestFullscreen, `platform=${p}`).toHaveBeenCalledOnce();
+    }
+  });
+
+  it('leaves desktop clients as a standard window (the bot full-size setting fills it)', () => {
+    for (const p of desktopPlatforms) {
+      const { requestFullscreen } = stubClient(p);
+      telegramRequestFullscreen();
+      expect(requestFullscreen, `platform=${p}`).not.toHaveBeenCalled();
+    }
+  });
+});

ui/src/lib/telegram.ts

@@ -16,6 +16,7 @@ interface TelegramWebApp {
   contentSafeAreaInset?: { top: number; bottom: number; left: number; right: number };
   ready?: () => void;
   expand?: () => void;
+  requestFullscreen?: () => void;
   openTelegramLink?: (url: string) => void;
   onEvent?: (event: string, handler: () => void) => void;
   setHeaderColor?: (color: string) => void;
@@ -167,13 +168,24 @@ export function telegramHaptic(kind: Haptic): void {
 }
 
 /**
- * isMobilePlatform reports whether the Mini App runs on a Telegram mobile client (iOS or
- * Android), where a stray swipe-down can drop the app. Desktop clients (tdesktop, macOS,
- * web) report other values and close only on a deliberate window action.
+ * isMobilePlatform reports whether the Mini App runs on a Telegram mobile client — iOS or
+ * Android (the latter reported as 'android' by Telegram for Android and 'android_x' by
+ * Telegram X). Desktop clients (tdesktop, macOS, web) report other values. Used to limit
+ * mobile-only chrome such as the close guard and immersive fullscreen.
  */
 function isMobilePlatform(): boolean {
   const p = webApp()?.platform;
-  return p === 'ios' || p === 'android';
+  return p === 'ios' || p === 'android' || p === 'android_x';
+}
+
+/**
+ * telegramRequestFullscreen asks Telegram to open the Mini App in fullscreen (Bot API 8.0+),
+ * but only on mobile clients — mirroring how Telegram's own Mini Apps go immersive on phones
+ * while staying a standard window on desktop (where the bot's full-size setting already fills
+ * the window). A no-op outside Telegram, on desktop, or on clients predating the method.
+ */
+export function telegramRequestFullscreen(): void {
+  if (isMobilePlatform()) webApp()?.requestFullscreen?.();
 }
 
 /**