diff --git a/ui/src/lib/transport.ts b/ui/src/lib/transport.ts
index 51bf052..f868d7d 100644
--- a/ui/src/lib/transport.ts
+++ b/ui/src/lib/transport.ts
@@ -12,6 +12,7 @@ import { GatewayError, type GatewayClient } from './client';
 import * as codec from './codec';
 import { browserOffset } from './profileValidation';
 import { registerProbe, reportOffline, reportOnline } from './connection.svelte';
+import { offlineMode } from './offline.svelte';
 import { maintenanceRecovered, registerMaintenanceProbe, reportMaintenance } from './maintenance.svelte';
 import { maintenanceRetryMs } from './maintenance';
 import { backoffMs, isConnectionCode, retryable, toGatewayError } from './retry';
@@ -19,6 +20,13 @@ import { backoffMs, isConnectionCode, retryable, toGatewayError } from './retry'
 const MAX_RETRIES = 6;
 const sleep = (ms: number): Promise<void> => new Promise((r) => setTimeout(r, ms));
 
+// The offline kill switch: in deliberate offline mode every network operation is refused before it
+// leaves the device, so offline truly means offline regardless of any UI affordance that slips
+// through. The local (device-only) game path never uses this transport, so it is unaffected.
+function assertOnline(): void {
+  if (offlineMode.active) throw new GatewayError('offline');
+}
+
 export function createTransport(baseUrl: string): GatewayClient {
   const origin = baseUrl || (typeof location !== 'undefined' ? location.origin : '');
   const transport = createConnectTransport({ baseUrl: origin, useBinaryFormat: true });
@@ -32,6 +40,7 @@ export function createTransport(baseUrl: string): GatewayClient {
   // (it must reject when there is no session, so the watcher keeps waiting rather than reporting up).
   const reachabilityProbe = async (): Promise<void> => {
     if (!token) throw new Error('no session');
+    assertOnline();
     await client.execute({ messageType: 'profile.get', payload: codec.empty(), requestId: '' }, { headers: headers() });
   };
   registerProbe(reachabilityProbe);
@@ -43,6 +52,7 @@ export function createTransport(baseUrl: string): GatewayClient {
   // dropped connection or a rate-limit recovers seamlessly) and driving the global Connecting
   // indicator. A successful round-trip marks the gateway reachable; a domain result_code is final.
   async function exec(messageType: string, payload: Uint8Array, signal?: AbortSignal): Promise<Uint8Array> {
+    assertOnline();
     for (let attempt = 0; ; attempt++) {
       let res;
       try {
@@ -82,6 +92,7 @@ export function createTransport(baseUrl: string): GatewayClient {
 
     async fetchDict(variant, version, opts) {
       if (!token) throw new Error('fetchDict: no session');
+      assertOnline();
       // Low priority so the browser schedules the (large) dictionary behind the game's own
       // requests — the move eval, state and live events — on a slow link (EDGE). Ignored
       // where the Priority Hints API is unsupported (iOS WebKit), which is harmless. The
@@ -99,6 +110,7 @@ export function createTransport(baseUrl: string): GatewayClient {
 
     async reportLocalEval(counts) {
       if (!token) throw new Error('reportLocalEval: no session');
+      assertOnline();
       // keepalive so a batch flushed as the app is backgrounded still reaches the edge.
       const res = await fetch(`${origin}/metrics/local-eval`, {
         method: 'POST',
@@ -319,6 +331,8 @@ export function createTransport(baseUrl: string): GatewayClient {
     },
 
     subscribe(onEvent, onError) {
+      // No live stream in offline mode (the kill switch); return an inert unsubscribe.
+      if (offlineMode.active) return () => {};
       const ctrl = new AbortController();
       void (async () => {
         try {
diff --git a/ui/src/screens/About.svelte b/ui/src/screens/About.svelte
index 62f3abc..fd653b6 100644
--- a/ui/src/screens/About.svelte
+++ b/ui/src/screens/About.svelte
@@ -2,6 +2,7 @@
   import { t } from '../lib/i18n/index.svelte';
   import { app } from '../lib/app.svelte';
   import { navigate } from '../lib/router.svelte';
+  import { offlineMode } from '../lib/offline.svelte';
   import { aboutContent } from '../lib/aboutContent';
   import { onExternalLinkClick } from '../lib/links';
 
@@ -35,7 +36,7 @@
   <p class="muted">{t('about.version', { v: version })}</p>
 
   {#if !(app.profile?.isGuest ?? true)}
-    <button class="feedback" onclick={() => navigate('/feedback')}>
+    <button class="feedback" disabled={offlineMode.active} onclick={() => navigate('/feedback')}>
       {t('feedback.title')}{#if app.feedbackReplyUnread}<span class="fbadge">1</span>{/if}
     </button>
   {/if}
diff --git a/ui/src/screens/SettingsHub.svelte b/ui/src/screens/SettingsHub.svelte
index b570fb2..a2934dc 100644
--- a/ui/src/screens/SettingsHub.svelte
+++ b/ui/src/screens/SettingsHub.svelte
@@ -6,6 +6,7 @@
   import Friends from './Friends.svelte';
   import About from './About.svelte';
   import { app } from '../lib/app.svelte';
+  import { offlineMode } from '../lib/offline.svelte';
   import { t, type MessageKey } from '../lib/i18n/index.svelte';
 
   // The Settings hub: a single nav bar + bottom tab bar hosting the Settings / Profile /
@@ -23,6 +24,12 @@
   $effect(() => {
     if (guest && tab === 'friends') tab = 'settings';
   });
+  // Offline mode has no network, so the Profile and Friends surfaces (which read/save over the
+  // network) are disabled — fall back to Settings if the hub is on one (a deep-link or a live flip).
+  // Settings stays reachable: it holds the online/offline toggle.
+  $effect(() => {
+    if (offlineMode.active && (tab === 'profile' || tab === 'friends')) tab = 'settings';
+  });
 
   const titleKey: Record<SettingsTab, MessageKey> = {
     settings: 'settings.title',
@@ -48,11 +55,11 @@
       <button class="tab" class:active={tab === 'settings'} onclick={() => (tab = 'settings')}>
         <span class="face"><span class="sq" aria-hidden="true">⚙️</span><span class="lbl">{t('settings.title')}</span></span>
       </button>
-      <button class="tab" class:active={tab === 'profile'} onclick={() => (tab = 'profile')}>
+      <button class="tab" class:active={tab === 'profile'} disabled={offlineMode.active} onclick={() => (tab = 'profile')}>
         <span class="face"><span class="sq" aria-hidden="true">👤</span><span class="lbl">{t('profile.title')}</span></span>
       </button>
       {#if !guest}
-        <button class="tab" class:active={tab === 'friends'} onclick={() => (tab = 'friends')}>
+        <button class="tab" class:active={tab === 'friends'} disabled={offlineMode.active} onclick={() => (tab = 'friends')}>
           <span class="face"><span class="sq" aria-hidden="true">🤝{#if app.notifications > 0}<span class="badge">{app.notifications}</span>{/if}</span><span class="lbl">{t('friends.title')}</span></span>
         </button>
       {/if}