diff --git a/ui/src/App.svelte b/ui/src/App.svelte
index 099dbe7..b7f54ad 100644
--- a/ui/src/App.svelte
+++ b/ui/src/App.svelte
@@ -4,7 +4,7 @@
   import { app, bootstrap } from './lib/app.svelte';
   import { navigate, router, type RouteName } from './lib/router.svelte';
   import { t } from './lib/i18n/index.svelte';
-  import { insideTelegram, telegramBackButton } from './lib/telegram';
+  import { insideTelegram, telegramBackButton, telegramChromeDiag } from './lib/telegram';
   import Toast from './components/Toast.svelte';
   import Splash from './components/Splash.svelte';
   import StaleInviteModal from './components/StaleInviteModal.svelte';
@@ -138,6 +138,14 @@
   <Splash />
 {/if}
 
+<!-- TEMP DIAGNOSTIC overlay (Android nav debug) — REMOVE before merge -->
+{#if app.ready && insideTelegram()}
+  {#key router.route.name + (router.route.params.id ?? '')}
+    <pre
+      style="position:fixed;left:0;right:0;bottom:0;z-index:9999;margin:0;padding:6px 8px;font:10px/1.35 ui-monospace,monospace;white-space:pre-wrap;overflow-wrap:anywhere;background:rgba(0,0,0,0.85);color:#3f3;max-height:45vh;overflow:auto;pointer-events:none">{telegramChromeDiag()}</pre>
+  {/key}
+{/if}
+
 <style>
   .splash {
     height: 100%;
diff --git a/ui/src/components/Header.svelte b/ui/src/components/Header.svelte
index d050e83..04d4a07 100644
--- a/ui/src/components/Header.svelte
+++ b/ui/src/components/Header.svelte
@@ -1,6 +1,6 @@
 <script lang="ts">
   import { navigate } from '../lib/router.svelte';
-  import { insideTelegram } from '../lib/telegram';
+  import { insideTelegram, isTelegramAndroid } from '../lib/telegram';
   import { connection } from '../lib/connection.svelte';
   import { t } from '../lib/i18n/index.svelte';
   import { app } from '../lib/app.svelte';
@@ -9,9 +9,10 @@
 
   let { title, back, grow = false }: { title: string; back?: string; grow?: boolean } = $props();
 
-  // Inside Telegram the native header back button (App.svelte) is the back control, so
-  // the app's own chevron is hidden to avoid two back affordances.
-  const showBack = $derived(!!back && !insideTelegram());
+  // Inside Telegram the native header back button (App.svelte) is the back control, so the app's
+  // own chevron is hidden to avoid two back affordances — except on Android, where the native
+  // BackButton does not render in the (non-fullscreen) presentation, so the app shows its own.
+  const showBack = $derived(!!back && (!insideTelegram() || isTelegramAndroid()));
 </script>
 
 <header class="nav" class:grow>
diff --git a/ui/src/lib/telegram.ts b/ui/src/lib/telegram.ts
index 9946896..2383a32 100644
--- a/ui/src/lib/telegram.ts
+++ b/ui/src/lib/telegram.ts
@@ -36,6 +36,7 @@ interface TelegramWebApp {
     selectionChanged?: () => void;
   };
   BackButton?: {
+    isVisible?: boolean;
     show?: () => void;
     hide?: () => void;
     onClick?: (cb: () => void) => void;
@@ -303,10 +304,22 @@ export function telegramHaptic(kind: Haptic): void {
  * Android, on desktop, or on clients predating the method.
  */
 export function telegramRequestFullscreen(): void {
-  if (webApp()?.platform === 'ios') webApp()?.requestFullscreen?.();
+  // TEMP (owner test): fullscreen fully disabled, incl. iOS, to confirm the Android "fullscreen
+  // look" is Telegram's own Mini App presentation, not our requestFullscreen (isFullscreen is
+  // already false on Android). Restore the iOS path after the test:
+  // if (webApp()?.platform === 'ios') webApp()?.requestFullscreen?.();
+}
+
+/** isTelegramAndroid reports whether the Mini App runs on a Telegram Android client (reported as
+ *  'android', or 'android_x' for Telegram X). The native header BackButton does not render in the
+ *  Android (non-fullscreen) presentation, so back navigation there uses the app's own chevron. */
+export function isTelegramAndroid(): boolean {
+  const p = webApp()?.platform;
+  return p === 'android' || p === 'android_x';
 }
 
 let backHandler: (() => void) | null = null;
+let lastBackShow = false; // TEMP diag: the last telegramBackButton(show) request
 
 /**
  * telegramBackButton shows or hides Telegram's native header back button, wiring its
@@ -314,6 +327,7 @@ let backHandler: (() => void) | null = null;
  * inside Telegram so only the native control shows.
  */
 export function telegramBackButton(show: boolean, onClick?: () => void): void {
+  lastBackShow = show;
   const b = webApp()?.BackButton;
   if (!b) return;
   if (backHandler) b.offClick?.(backHandler);
@@ -481,14 +495,22 @@ export function collectTelegramDiag(): TelegramDiag {
 export function telegramChromeDiag(): string {
   const w = webApp();
   if (!w) return 'no telegram';
-  const ih = typeof window === 'undefined' ? 0 : window.innerHeight;
-  const sh = typeof screen === 'undefined' ? 0 : screen.height;
+  const win = typeof window === 'undefined' ? undefined : window;
+  const scr = typeof screen === 'undefined' ? undefined : screen;
+  const vv = win?.visualViewport ?? undefined;
+  const bar = typeof document === 'undefined' ? null : (document.querySelector('.bar')?.getBoundingClientRect() ?? null);
+  const sa = w.safeAreaInset;
+  const csa = w.contentSafeAreaInset;
+  const n = (v: number | undefined): string => (v === undefined ? '—' : String(Math.round(v)));
   return [
-    `platform: ${w.platform ?? '—'}  version: ${w.version ?? '—'}`,
+    `platform: ${w.platform ?? '—'}  version: ${w.version ?? '—'}  scheme: ${w.colorScheme ?? '—'}`,
     `isFullscreen: ${w.isFullscreen}  isExpanded: ${w.isExpanded}`,
-    `viewportH: ${w.viewportHeight ?? '—'}  stableH: ${w.viewportStableHeight ?? '—'}`,
-    `innerH: ${ih}  screenH: ${sh}`,
-    `contentSafeTop: ${w.contentSafeAreaInset?.top ?? '—'}  safeTop: ${w.safeAreaInset?.top ?? '—'}`,
+    `inTG: ${insideTelegram()}  backReq: ${lastBackShow}  backPresent: ${!!w.BackButton}  backVisible: ${w.BackButton?.isVisible}`,
+    `innerH: ${n(win?.innerHeight)}  outerH: ${n(win?.outerHeight)}  screenH: ${n(scr?.height)}  availH: ${n(scr?.availHeight)}`,
+    `screenY: ${n(win?.screenY)}  vv.offTop: ${n(vv?.offsetTop)}  vv.h: ${n(vv?.height)}`,
+    `tgViewportH: ${n(w.viewportHeight)}  stableH: ${n(w.viewportStableHeight)}`,
+    `safeArea T/B: ${n(sa?.top)}/${n(sa?.bottom)}  contentSafe T/B: ${n(csa?.top)}/${n(csa?.bottom)}`,
+    `appHeader top/h: ${bar ? Math.round(bar.top) : '—'}/${bar ? Math.round(bar.height) : '—'}`,
   ].join('\n');
 }
 
diff --git a/ui/src/screens/Lobby.svelte b/ui/src/screens/Lobby.svelte
index af3fd3e..b06ba42 100644
--- a/ui/src/screens/Lobby.svelte
+++ b/ui/src/screens/Lobby.svelte
@@ -9,7 +9,6 @@
   import { gateway } from '../lib/gateway';
   import { navigate } from '../lib/router.svelte';
   import { t } from '../lib/i18n/index.svelte';
-  import { insideTelegram, telegramChromeDiag } from '../lib/telegram'; // TEMP diag — remove before merge
   import { resultBadge } from '../lib/result';
   import { badgeKind } from '../lib/unread';
   import { getLobby, setLobby } from '../lib/lobbycache';
@@ -224,12 +223,6 @@
 
 <Screen title={app.profile?.displayName ?? t('app.title')}>
   <div class="lobby">
-    <!-- TEMP DIAGNOSTIC (Android fullscreen debug) — REMOVE before merge -->
-    {#if insideTelegram()}
-      <pre
-        style="margin:0 0 8px;padding:8px;font:11px/1.4 ui-monospace,monospace;white-space:pre-wrap;overflow-wrap:anywhere;background:var(--bg-elev);border:1px solid var(--border);border-radius:var(--radius-sm);color:var(--text)"
-      >{telegramChromeDiag()}</pre>
-    {/if}
     {#if invitations.length}
       <section>
         <h2>{t('lobby.invitations')}</h2>