ui/src/game/Game.svelte

@@ -13,6 +13,7 @@
   import { navigate } from '../lib/router.svelte';
   import { app, handleError, showToast, markChatRead, seedChatUnread } from '../lib/app.svelte';
   import { connection } from '../lib/connection.svelte';
+  import { offlineMode } from '../lib/offline.svelte';
   import { GatewayError } from '../lib/client';
   import { t, type MessageKey } from '../lib/i18n/index.svelte';
   import type { EvalResult, MoveRecord, MoveResult, StateView, Tile } from '../lib/model';
@@ -52,6 +53,11 @@
   // screen calls the game-loop methods (state/history/submit/pass/exchange/resign/hint/evaluate/
   // draft) through it, so the same UI drives a local vs_ai game and an online one alike.
   const source = $derived(gameSource(id));
+  // A local (offline) game plays entirely on-device, so it is always ready; an online game needs a
+  // live connection — and offline mode's kill switch refuses its calls — so its network actions are
+  // disabled while disconnected or in offline mode (which also stops the "something went wrong"
+  // toasts a blocked call would otherwise raise).
+  const netReady = $derived(isLocalGameId(id) || (connection.online && !offlineMode.active));
   // Unsubscribes from a local game's robot-reply events (offline only; null for a network game).
   let localUnsub: (() => void) | null = null;
 
@@ -1481,19 +1487,19 @@
       />
     </div>
     {#if !gameOver && placement.pending.length > 0 && !recallOverRack}
-      <button class="make" onclick={commit} disabled={busy || !isMyTurn || !connection.online || !preview?.legal} aria-label={t('game.makeMove')}>✅</button>
+      <button class="make" onclick={commit} disabled={busy || !isMyTurn || !netReady || !preview?.legal} aria-label={t('game.makeMove')}>✅</button>
     {/if}
   </div>
 {/snippet}
 
 {#snippet controlButtons()}
-  <button class="tab" disabled={busy || !isMyTurn || !connection.online} onclick={openExchange}>
+  <button class="tab" disabled={busy || !isMyTurn || !netReady} onclick={openExchange}>
     <span class="sq" data-coach="game-turn">🔄</span><span class="lbl">{t('game.draw')}</span>
   </button>
   <TapConfirm
     triggerClass="tab"
     label={t('game.hint')}
-    disabled={busy || !isMyTurn || !connection.online || hintCount <= 0}
+    disabled={busy || !isMyTurn || !netReady || hintCount <= 0}
     onconfirm={doHint}
   >
     <span class="sq" data-coach="game-hints">🛟{#if hintCount > 0}<span class="badge">{hintCount}</span>{/if}</span>
@@ -1551,7 +1557,7 @@
   <Modal title={t('game.confirmResign')} onclose={() => (resignOpen = false)}>
     <div class="confirm-row">
       <button class="cancel" onclick={() => (resignOpen = false)}>{t('common.cancel')}</button>
-      <button class="danger" onclick={doResign} disabled={!connection.online}>{t('game.dropGame')}</button>
+      <button class="danger" onclick={doResign} disabled={!netReady}>{t('game.dropGame')}</button>
     </div>
   </Modal>
 {/if}
@@ -1563,7 +1569,7 @@
         <button
           class="confirm"
           onclick={() => { exportOpen = false; void exportArtifact('png'); }}
-          disabled={!connection.online}
+          disabled={!netReady}
         >
           {t('game.exportImageOpt')}
         </button>
@@ -1571,7 +1577,7 @@
       <button
         class={exportImageAvailable ? 'export-alt' : 'confirm'}
         onclick={() => { exportOpen = false; void exportArtifact('gcg'); }}
-        disabled={!connection.online}
+        disabled={!netReady}
       >
         {t('game.exportGcgOpt')}
       </button>

ui/src/lib/app.svelte.ts

@@ -304,7 +304,9 @@ export function handleError(err: unknown): void {
     void enterBlocked();
     return;
   }
-  if (isConnectionCode(code) || !connection.online) return;
+  // A blocked call in offline mode ('offline', the transport kill switch) is expected, not an error
+  // to surface — the offline chrome already signals the state; never a red toast.
+  if (isConnectionCode(code) || code === 'offline' || !connection.online) return;
   haptic('error');
   showToast(t(code ? errorKey(code) : 'error.generic'), 'error');
 }
@@ -577,6 +579,53 @@ function promptOfflineChoice(): Promise<boolean> {
   });
 }
 
+/**
+ * initNetworkReactivity reacts to mid-session network changes (e.g. the player toggling flight mode):
+ * losing the network interface enters offline mode automatically (session-only); regaining it
+ * verifies the gateway is really reachable (an interface being up does not guarantee it) and returns
+ * to online — but only if the offline was auto. A deliberate offline (the Settings toggle or the
+ * cold-start dialog) is left as the player's choice. These are passive OS events — no polling, no
+ * battery cost. Web-only and skipped in the mock (the e2e drives connectivity directly).
+ */
+// While in auto-offline, poll for the network to return so the app comes back online — robust to the
+// unreliable `online` event (which often does not fire in an installed PWA). Each tick is cheap: it
+// reads navigator.onLine (no radio) and only hits the network (a reachability check) when the
+// interface is actually up, so while flight mode is on it costs nothing. The poll runs ONLY in
+// auto-offline (a deliberate offline is the player's choice) and stops on returning online.
+let recoveryTimer: ReturnType<typeof setTimeout> | null = null;
+export function scheduleRecovery(delayMs: number): void {
+  if (recoveryTimer) {
+    clearTimeout(recoveryTimer);
+    recoveryTimer = null;
+  }
+  if (typeof window === 'undefined' || !offlineMode.active || !offlineMode.auto) return;
+  recoveryTimer = setTimeout(async () => {
+    recoveryTimer = null;
+    if (!offlineMode.active || !offlineMode.auto) return;
+    const interfaceUp = typeof navigator === 'undefined' || navigator.onLine;
+    if (interfaceUp && (await checkReachable(BOOT_REACHABILITY_TIMEOUT_MS))) {
+      if (offlineMode.active && offlineMode.auto) setOfflineMode(false);
+      return;
+    }
+    scheduleRecovery(4000);
+  }, delayMs);
+}
+
+export function initNetworkReactivity(): void {
+  if (typeof window === 'undefined' || import.meta.env.MODE === 'mock') return;
+  window.addEventListener('offline', () => {
+    if (!offlineMode.active) {
+      setOfflineMode(true, false); // auto (session)
+      scheduleRecovery(4000); // poll for the network to return
+    }
+  });
+  // The online event, when it fires, just kicks an immediate reachability check; the poll above is
+  // the reliable fallback for platforms where it does not fire.
+  window.addEventListener('online', () => {
+    if (offlineMode.active && offlineMode.auto) scheduleRecovery(0);
+  });
+}
+
 /**
  * applyLinkResult applies a completed account link or merge: it adopts a
  * switched session (a guest initiator whose durable counterpart won, so the active
@@ -826,6 +875,8 @@ export async function bootstrap(): Promise<void> {
   // worker so the app is installable — Chromium needs a registered SW, notably on Android. Web-only
   // and skipped in the mock build; see lib/pwa.svelte.
   registerServiceWorker();
+  // React to mid-session network changes (e.g. flight mode) for the rest of the session.
+  initNetworkReactivity();
 
   // Deliberate offline mode carried over from a prior session: with no network the session adoption
   // + profile fetch below would hang the splash, so skip them and launch straight from the cached
@@ -868,6 +919,7 @@ export async function bootstrap(): Promise<void> {
         if (goOffline) {
           // A deliberate dialog choice is sticky; an auto (no-interface) offline is session-only.
           setOfflineMode(true, !interfaceOffline);
+          if (interfaceOffline) scheduleRecovery(4000); // auto-offline: poll for the network to return
           app.session = saved;
           app.profile = cachedProfile;
           if (router.route.name === 'login' || router.route.name === 'confirm') navigate('/');

ui/src/lib/connection.svelte.ts

@@ -9,6 +9,7 @@
 // other traffic is in flight.
 
 import { backoffMs } from './retry';
+import { offlineMode } from './offline.svelte';
 
 let online = $state(true);
 let watchTimer: ReturnType<typeof setTimeout> | null = null;
@@ -39,10 +40,8 @@ export async function checkReachable(timeoutMs: number): Promise<boolean> {
       probe(),
       new Promise<never>((_, reject) => setTimeout(() => reject(new Error('reachability timeout')), timeoutMs)),
     ]);
-    reportOnline();
     return true;
   } catch {
-    reportOffline();
     return false;
   }
 }
@@ -71,7 +70,9 @@ function scheduleProbe(attempt: number): void {
   watchTimer = setTimeout(
     () => {
       watchTimer = null;
-      if (online || !probe) return;
+      // Never probe the network in offline mode (the kill switch); the online/offline events drive
+      // recovery there instead.
+      if (online || !probe || offlineMode.active) return;
       probe().then(reportOnline, () => scheduleProbe(Math.min(attempt + 1, 6)));
     },
     backoffMs(attempt),

ui/src/lib/offline.svelte.ts

@@ -11,13 +11,21 @@ import type { Profile } from './model';
 
 // Not named `state` (a svelte-check hazard: `$state` would then read as a store subscription).
 let active = $state(loadOfflinePref());
+// True while the current offline state was entered automatically (no network detected), not chosen
+// by the player. An auto offline self-heals to online when the network returns; a deliberate one is
+// left as the player's choice.
+let auto = $state(false);
 
-/** offlineMode exposes the reactive deliberate-offline flag; read it in markup / $derived. */
+/** offlineMode exposes the reactive offline flags; read them in markup / $derived. */
 export const offlineMode = {
-  /** active is true while the app is in deliberate offline mode. */
+  /** active is true while the app is in offline mode (deliberate or auto-detected). */
   get active(): boolean {
     return active;
   },
+  /** auto is true while offline was entered automatically (no network), not by the player. */
+  get auto(): boolean {
+    return auto;
+  },
 };
 
 /**
@@ -28,6 +36,7 @@ export const offlineMode = {
  */
 export function setOfflineMode(on: boolean, persist = true): void {
   active = on;
+  auto = on && !persist; // a non-persisted offline is auto-detected; a persisted one is deliberate
   if (persist) saveOfflinePref(on);
 }
 

ui/src/lib/transport.ts

@@ -40,7 +40,9 @@ 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();
+    // Exempt from the offline kill switch: the probe IS the reachability check that decides whether to
+    // return online, and it fires only deliberately — the connection watcher is guarded off in offline
+    // mode, and checkReachable runs it on an online event — so it must reach the gateway while offline.
     await client.execute({ messageType: 'profile.get', payload: codec.empty(), requestId: '' }, { headers: headers() });
   };
   registerProbe(reachabilityProbe);