fix(offline): return online after flight-mode off; gate online-game actions offline

Two mid-session issues found on the contour:
- Auto-offline did not return to online after the network came back: a single
  reachability check right after the 'online' event failed (the interface is up
  before the gateway is actually reachable again). Retry a few times with backoff
  (tryReturnOnline) — that is what actually gets the app back online.
- An online game viewed while offline (flight mode on) still enabled its network
  actions, so they hit the kill switch and raised 'something went wrong' toasts.
  Gate them: netReady = isLocalGame || (connection.online && !offlineMode.active)
  — a local game stays fully usable; an online game's make/exchange/hint/resign
  disable while offline and re-enable when back. Also suppress the 'offline' code
  in handleError (a blocked call in offline mode is expected, not a toast).

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');
 }
@@ -585,18 +587,28 @@ function promptOfflineChoice(): Promise<boolean> {
  * 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).
  */
+// tryReturnOnline is fired from the online event while in auto-offline: the interface being back does
+// not mean the gateway is reachable yet (DNS/routing settle for a moment after flight mode), so it
+// re-checks a few times with backoff before returning online, stopping if the player takes over the
+// state meanwhile. This bounded retry is what actually gets the app back online after flight mode off.
+async function tryReturnOnline(): Promise<void> {
+  for (let attempt = 0; attempt < 4; attempt++) {
+    if (!offlineMode.active || !offlineMode.auto) return;
+    if (await checkReachable(BOOT_REACHABILITY_TIMEOUT_MS)) {
+      if (offlineMode.active && offlineMode.auto) setOfflineMode(false);
+      return;
+    }
+    await new Promise((r) => setTimeout(r, 600 * (attempt + 1)));
+  }
+}
+
 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) — self-heals below
   });
   window.addEventListener('online', () => {
-    if (offlineMode.active && offlineMode.auto) {
+    if (offlineMode.active && offlineMode.auto) void tryReturnOnline();
-      void checkReachable(BOOT_REACHABILITY_TIMEOUT_MS).then((reachable) => {
-        // Re-read the flags — the player may have chosen offline meanwhile — before returning online.
-        if (reachable && offlineMode.active && offlineMode.auto) setOfflineMode(false);
-      });
-    }
   });
 }