diff --git a/ui/scripts/bundle-size.mjs b/ui/scripts/bundle-size.mjs
index 2cf27c9..75f7f9e 100644
--- a/ui/scripts/bundle-size.mjs
+++ b/ui/scripts/bundle-size.mjs
@@ -20,12 +20,12 @@ import { join } from 'node:path';
 const DIST = 'dist';
 
 // Per-chunk gzip budgets in KB. The app entry was raised to 110 for the local move-preview
-// wiring, to 112 for the PWA install feature, then to 113 for the offline-mode wiring: the
-// dictionary-preload trigger and the offline-state reactives live in the app entry (the Header
-// reads them, the lobby/profile screens fire the trigger), while the heavy parts — the dict
-// loader, the move generator and the preload orchestration — stay in lazy chunks. Scoped CSS
-// lands in the CSS chunk, not this JS budget.
-const BUDGET = { app: 113, shared: 30, landing: 5 };
+// wiring, to 112 for the PWA install feature, to 113 for the offline-mode wiring, then to 114 for
+// the offline auto-detect: the cold-start reachability check and the "no connection" dialog live in
+// the boot path (app.svelte.ts / the App shell), which cannot be lazy-loaded. The heavy parts — the
+// dict loader, the move generator and the preload orchestration — still stay in lazy chunks. Scoped
+// CSS lands in the CSS chunk, not this JS budget.
+const BUDGET = { app: 114, shared: 30, landing: 5 };
 
 // gzipped returns the gzipped byte size of a built asset, or 0 when the reference is not a
 // local file (e.g. the Telegram SDK loaded from a CDN) or is missing.
diff --git a/ui/src/App.svelte b/ui/src/App.svelte
index 39bd17e..734fd81 100644
--- a/ui/src/App.svelte
+++ b/ui/src/App.svelte
@@ -1,7 +1,7 @@
 <script lang="ts">
   import { onMount } from 'svelte';
   import { cubicOut } from 'svelte/easing';
-  import { app, bootstrap } from './lib/app.svelte';
+  import { app, bootstrap, resolveOfflinePrompt } from './lib/app.svelte';
   import { router, type RouteName } from './lib/router.svelte';
   import { t } from './lib/i18n/index.svelte';
   import Toast from './components/Toast.svelte';
@@ -136,6 +136,21 @@
 <Coachmark />
 <MaintenanceOverlay />
 
+<!-- Cold-start "no connection" dialog: the reachability check timed out with the network interface
+     reportedly online, so it is ambiguous. The player chooses to go offline (play local vs_ai) or to
+     keep trying to connect. bootstrap awaits this choice (app.offlinePrompt). -->
+{#if app.offlinePrompt}
+  <div class="offprompt" role="dialog" aria-modal="true">
+    <div class="card">
+      <p class="msg">{t('offline.promptTitle')}</p>
+      <div class="acts">
+        <button class="opt primary" onclick={() => resolveOfflinePrompt(true)}>{t('offline.promptYes')}</button>
+        <button class="opt" onclick={() => resolveOfflinePrompt(false)}>{t('offline.promptNo')}</button>
+      </div>
+    </div>
+  </div>
+{/if}
+
 {#if routeIsLobby && !app.splashDone && !app.blocked && !app.bootError && !app.launchError}
   <Splash />
 {/if}
@@ -145,6 +160,49 @@
 {/if}
 
 <style>
+  /* The cold-start "no connection" dialog — a centred card over a scrim, above the splash. */
+  .offprompt {
+    position: fixed;
+    inset: 0;
+    z-index: 100;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    background: rgba(0, 0, 0, 0.5);
+    padding: var(--pad);
+  }
+  .offprompt .card {
+    background: var(--bg-elev);
+    border: 1px solid var(--border);
+    border-radius: var(--radius-sm);
+    padding: 20px;
+    max-width: 320px;
+    width: 100%;
+    text-align: center;
+  }
+  .offprompt .msg {
+    margin: 0 0 16px;
+    font-size: 1rem;
+    color: var(--text);
+  }
+  .offprompt .acts {
+    display: flex;
+    flex-direction: column;
+    gap: 8px;
+  }
+  .offprompt .opt {
+    padding: 11px 16px;
+    border: 1px solid var(--border);
+    border-radius: var(--radius-sm);
+    background: var(--surface);
+    color: var(--text);
+    font-size: 0.95rem;
+  }
+  .offprompt .opt.primary {
+    background: var(--accent);
+    color: var(--accent-text);
+    border-color: var(--accent);
+  }
   .splash {
     height: 100%;
     display: grid;
diff --git a/ui/src/lib/app.svelte.ts b/ui/src/lib/app.svelte.ts
index 58ed777..77ef40c 100644
--- a/ui/src/lib/app.svelte.ts
+++ b/ui/src/lib/app.svelte.ts
@@ -55,8 +55,8 @@ import {
   savePrefs,
 } from './session';
 import type { CoachSeries } from './coachmark';
-import { connection, reportOffline, reportOnline, resetConnection } from './connection.svelte';
-import { offlineMode } from './offline.svelte';
+import { connection, reportOffline, reportOnline, resetConnection, checkReachable } from './connection.svelte';
+import { offlineMode, setOfflineMode } from './offline.svelte';
 import { shouldBootOffline } from './offline';
 import { isConnectionCode } from './retry';
 import { clearGameCache, getCachedGame, setCachedGame } from './gamecache';
@@ -78,6 +78,10 @@ export const app = $state<{
    *  backend was down during a deploy). App.svelte then renders the boot-error retry screen
    *  instead of the web login — a Mini App has no manual sign-in to fall back to. */
   bootError: boolean;
+  /** True while the cold-start "no connection — go offline?" dialog is up (the reachability check
+   *  timed out with the network interface reportedly online). App.svelte renders it over the splash;
+   *  bootstrap awaits the choice via resolveOfflinePrompt. */
+  offlinePrompt: boolean;
   /** On the dedicated /telegram/ entry, set to a privacy-safe diagnostic snapshot when a Mini App
    *  launch carried no sign-in data (empty initData). App.svelte then renders the compact
    *  launch-error screen (screens/TelegramLaunchError) — a shareable probe for why Telegram
@@ -148,6 +152,7 @@ export const app = $state<{
 }>({
   ready: false,
   bootError: false,
+  offlinePrompt: false,
   launchError: null,
   debugOpen: false,
   lobbyReady: false,
@@ -551,6 +556,27 @@ async function adoptSession(s: Session): Promise<void> {
   void refreshNotifications();
 }
 
+// The cold-start "no connection — go offline?" dialog. bootstrap raises it and awaits the choice
+// here; App.svelte's dialog buttons call resolveOfflinePrompt.
+const BOOT_REACHABILITY_TIMEOUT_MS = 3000;
+let offlinePromptResolve: ((goOffline: boolean) => void) | null = null;
+
+/** resolveOfflinePrompt answers the cold-start "no connection — go offline?" dialog (App.svelte). */
+export function resolveOfflinePrompt(goOffline: boolean): void {
+  app.offlinePrompt = false;
+  const resolve = offlinePromptResolve;
+  offlinePromptResolve = null;
+  resolve?.(goOffline);
+}
+
+/** promptOfflineChoice raises the dialog and resolves to the player's choice (true = go offline). */
+function promptOfflineChoice(): Promise<boolean> {
+  app.offlinePrompt = true;
+  return new Promise<boolean>((resolve) => {
+    offlinePromptResolve = resolve;
+  });
+}
+
 /**
  * applyLinkResult applies a completed account link or merge: it adopts a
  * switched session (a guest initiator whose durable counterpart won, so the active
@@ -824,6 +850,34 @@ export async function bootstrap(): Promise<void> {
   // from VK; capture and clear it here (it needs the restored session to link against).
   const vkcb = pendingVKLink();
   if (saved) {
+    // Cold-start network auto-detect (deliberate offline is handled above). With a cached profile to
+    // fall back on and no pending VK-link, do not hang on adoptSession's retrying profile fetch when
+    // the network is down: a device with no network interface goes offline for the session (no
+    // dialog); an interface that is up but cannot reach the gateway within a short window asks the
+    // player. Web-only reaches here (the Mini-App branches returned above), so isStandalone gates it.
+    const cachedProfile = await loadProfile();
+    const canOffline = !!cachedProfile && !vkcb && isStandalone() && !!cachedProfile.email;
+    if (canOffline) {
+      const interfaceOffline = typeof navigator !== 'undefined' && navigator.onLine === false;
+      gateway.setToken(saved.token);
+      const reachable = interfaceOffline ? false : await checkReachable(BOOT_REACHABILITY_TIMEOUT_MS);
+      if (!reachable) {
+        // No network interface → go offline for the session (no dialog); interface up but the
+        // gateway is unreachable → ambiguous, so ask.
+        const goOffline = interfaceOffline ? true : await promptOfflineChoice();
+        if (goOffline) {
+          // A deliberate dialog choice is sticky; an auto (no-interface) offline is session-only.
+          setOfflineMode(true, !interfaceOffline);
+          app.session = saved;
+          app.profile = cachedProfile;
+          if (router.route.name === 'login' || router.route.name === 'confirm') navigate('/');
+          app.ready = true;
+          return;
+        }
+        // "Нет" — keep trying online: fall through to adoptSession (it retries; the connection
+        // watcher shows "Connecting…").
+      }
+    }
     await adoptSession(saved);
     if (vkcb) {
       // The full-page redirect lost the in-app route, so hand the callback to Profile, which
diff --git a/ui/src/lib/connection.svelte.ts b/ui/src/lib/connection.svelte.ts
index 0612ea1..84c43b1 100644
--- a/ui/src/lib/connection.svelte.ts
+++ b/ui/src/lib/connection.svelte.ts
@@ -27,6 +27,26 @@ export function registerProbe(fn: () => Promise<void>): void {
   probe = fn;
 }
 
+/**
+ * checkReachable runs the reachability probe once, bounded by timeoutMs, and reports whether the
+ * gateway answered — a single attempt (no retry loop), for the cold-start network decision — while
+ * updating the online signal. It reports false when no probe is registered or the timeout wins.
+ */
+export async function checkReachable(timeoutMs: number): Promise<boolean> {
+  if (!probe) return false;
+  try {
+    await Promise.race([
+      probe(),
+      new Promise<never>((_, reject) => setTimeout(() => reject(new Error('reachability timeout')), timeoutMs)),
+    ]);
+    reportOnline();
+    return true;
+  } catch {
+    reportOffline();
+    return false;
+  }
+}
+
 /** reportOnline marks the gateway reachable and stops the watcher. */
 export function reportOnline(): void {
   online = true;
diff --git a/ui/src/lib/i18n/en.ts b/ui/src/lib/i18n/en.ts
index d25c417..0a7a73f 100644
--- a/ui/src/lib/i18n/en.ts
+++ b/ui/src/lib/i18n/en.ts
@@ -218,6 +218,9 @@ export const en = {
   'settings.online': 'Online',
   'settings.offline': 'Offline',
   'offline.preloadWarning': 'Poor internet connection. Some features may be unavailable.',
+  'offline.promptTitle': 'No connection. Enable offline mode?',
+  'offline.promptYes': 'Enable',
+  'offline.promptNo': 'Keep trying',
 
   'about.title': 'About',
   'about.tab': 'Info',
diff --git a/ui/src/lib/i18n/ru.ts b/ui/src/lib/i18n/ru.ts
index f34e946..6c354c9 100644
--- a/ui/src/lib/i18n/ru.ts
+++ b/ui/src/lib/i18n/ru.ts
@@ -218,6 +218,9 @@ export const ru: Record<MessageKey, string> = {
   'settings.online': 'Онлайн',
   'settings.offline': 'Оффлайн',
   'offline.preloadWarning': 'Плохое соединение с интернет. Некоторые функции могут быть недоступны.',
+  'offline.promptTitle': 'Нет связи. Включить офлайн-режим?',
+  'offline.promptYes': 'Включить',
+  'offline.promptNo': 'Ждать сеть',
 
   'about.title': 'О программе',
   'about.tab': 'Инфо',
diff --git a/ui/src/lib/offline.svelte.ts b/ui/src/lib/offline.svelte.ts
index 1c4e1cb..bcd3434 100644
--- a/ui/src/lib/offline.svelte.ts
+++ b/ui/src/lib/offline.svelte.ts
@@ -20,10 +20,15 @@ export const offlineMode = {
   },
 };
 
-/** setOfflineMode enters or leaves offline mode and persists the choice (device-scoped). */
-export function setOfflineMode(on: boolean): void {
+/**
+ * setOfflineMode enters or leaves offline mode. By default it persists the choice (device-scoped) —
+ * a deliberate choice (the Settings toggle, or the cold-start "no connection" dialog). Pass
+ * persist=false for a transient, auto-detected offline (a cold start with no network interface): the
+ * flag holds for the session but is not saved, so the next launch re-evaluates the network.
+ */
+export function setOfflineMode(on: boolean, persist = true): void {
   active = on;
-  saveOfflinePref(on);
+  if (persist) saveOfflinePref(on);
 }
 
 // The dict-preload warning: true when a first-lobby background preload could not fetch every