feat(ui): app-shell behaviour — restore validation, return-to-lobby, push

- A restored game that no longer exists (cancelled/removed/revoked) drops to
  the lobby with a toast instead of the in-game error state: game-state
  exposes a `notFound` flag and the shell redirects via appScreen.go("lobby").
- Add a visible "return to lobby" control to the in-game header.
- Push/toast deep-links use activeView.select(...) (no URL); fix a latent
  visibility-listener double-install on in-place game switches.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/frontend/src/lib/game-state.svelte.ts

@@ -118,6 +118,17 @@ export class GameStateStore {
 	 */
 	mapToggles: MapToggles = $state({ ...DEFAULT_MAP_TOGGLES });
 	error: string | null = $state(null);
+	/**
+	 * notFound is the distinct "this game is not in the player's list"
+	 * signal, set when `findGame` returns null (cancelled, removed, or
+	 * access revoked). It is a clean flag the app-shell reads after
+	 * `init` to drop a restored/stale game back to the lobby with a
+	 * toast, rather than string-matching the `error` message. Transient
+	 * network failures keep `notFound` false (they take the catch path)
+	 * so they still surface the in-game error state for a retry. Reset
+	 * to false at the start of every `setGame` / `advanceToPending`.
+	 */
+	notFound = $state(false);
 	/**
 	 * currentTurn mirrors the engine's turn number for the running
 	 * game (lifted from the lobby record on `setGame`). Phase 14
@@ -218,6 +229,7 @@ export class GameStateStore {
 		this.gameId = gameId;
 		this.status = "loading";
 		this.error = null;
+		this.notFound = false;
 		this.report = null;
 
 		this.wrapMode = await readWrapMode(this.cache, gameId);
@@ -229,6 +241,7 @@ export class GameStateStore {
 			if (summary === null) {
 				this.status = "error";
 				this.error = `game ${gameId} is not in your list`;
+				this.notFound = true;
 				return;
 			}
 			this.gameName = summary.gameName;
@@ -306,11 +319,13 @@ export class GameStateStore {
 		}
 		this.status = "loading";
 		this.error = null;
+		this.notFound = false;
 		try {
 			const summary = await this.findGame(this.gameId);
 			if (summary === null) {
 				this.status = "error";
 				this.error = `game ${this.gameId} is not in your list`;
+				this.notFound = true;
 				return;
 			}
 			this.gameName = summary.gameName;
@@ -558,6 +573,18 @@ export class GameStateStore {
 
 	private installVisibilityListener(): void {
 		if (typeof document === "undefined") return;
+		// Idempotent on re-init. In the single-URL app-shell a direct
+		// game → game switch (a push deep-link or a refresh-restore)
+		// re-runs `init` without unmounting the shell, so a naive
+		// `addEventListener` here would stack a second listener on every
+		// switch. Drop any previously-registered one first so exactly one
+		// stays live.
+		if (this.visibilityListener !== null) {
+			document.removeEventListener(
+				"visibilitychange",
+				this.visibilityListener,
+			);
+		}
 		const listener = (): void => {
 			if (document.visibilityState === "visible" && this.status === "ready") {
 				void this.refresh();

ui/frontend/src/lib/game/game-shell.svelte

@@ -515,6 +515,25 @@ return to the lobby still disposes the stores via `onDestroy`.
 					orderDraft.init({ cache, gameId: activeGameId }),
 					mailStore.init({ client, cache, gameId: activeGameId }),
 				]);
+				// A restored or stale game id may point at a game that is
+				// no longer in the player's list (cancelled, removed, or
+				// access revoked). `init` flags that distinct case via
+				// `gameState.notFound` (a transient network error keeps it
+				// false and surfaces the in-game error state instead). Drop
+				// to the lobby with a toast rather than stranding the user
+				// on the in-game "not in your list" error. Leaving the
+				// `game` screen unmounts the shell, so the stores are
+				// disposed via `onDestroy`; the rest of the bootstrap
+				// (client bind, server hydration) is skipped for the dead
+				// game.
+				if (gameState.notFound) {
+					appScreen.go("lobby");
+					toast.show({
+						messageKey: "game.events.unavailable.message",
+						durationMs: 8000,
+					});
+					return;
+				}
 				galaxyClient.set(client);
 				orderDraft.bindClient(client, {
 					getCurrentTurn: () => gameState.currentTurn,

ui/frontend/src/lib/header/header.svelte

@@ -18,6 +18,7 @@ absent until Phase 24 wires push-event state.
 <script lang="ts">
 	import { getContext } from "svelte";
 	import { i18n } from "$lib/i18n/index.svelte";
+	import { appScreen } from "$lib/app-nav.svelte";
 	import {
 		GAME_STATE_CONTEXT_KEY,
 		type GameStateStore,
@@ -56,6 +57,14 @@ absent until Phase 24 wires push-event state.
 		<TurnNavigator />
 	</div>
 	<div class="right">
+		<button
+			type="button"
+			class="return-to-lobby"
+			data-testid="return-to-lobby"
+			onclick={() => appScreen.go("lobby")}
+		>
+			{i18n.t("game.shell.menu.return_to_lobby")}
+		</button>
 		<button
 			type="button"
 			class="sidebar-toggle"
@@ -101,6 +110,20 @@ absent until Phase 24 wires push-event state.
 		overflow: hidden;
 		text-overflow: ellipsis;
 	}
+	.return-to-lobby {
+		font: inherit;
+		font-size: 0.85rem;
+		padding: 0.25rem 0.6rem;
+		background: transparent;
+		color: inherit;
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-sm);
+		cursor: pointer;
+		white-space: nowrap;
+	}
+	.return-to-lobby:hover {
+		background: var(--color-surface-hover);
+	}
 	.sidebar-toggle {
 		font: inherit;
 		font-size: 1.1rem;

ui/frontend/src/lib/i18n/locales/en.ts

@@ -29,6 +29,7 @@ const en = {
 	"game.events.turn_ready.message": "turn {turn} is ready",
 	"game.events.turn_ready.action": "view now",
 	"game.events.signature_failed": "verification failed, reconnecting…",
+	"game.events.unavailable.message": "this game is no longer available",
 
 	"login.title": "sign in to Galaxy",
 	"login.email_label": "email",
@@ -118,6 +119,7 @@ const en = {
 	"game.shell.menu.theme_light": "light",
 	"game.shell.menu.theme_dark": "dark",
 	"game.shell.menu.language": "language",
+	"game.shell.menu.return_to_lobby": "return to lobby",
 	"game.shell.menu.logout": "logout",
 	"game.shell.coming_soon": "coming soon",
 	"game.shell.turn.label": "turn {turn}",

ui/frontend/src/lib/i18n/locales/ru.ts

@@ -30,6 +30,7 @@ const ru: Record<keyof typeof en, string> = {
 	"game.events.turn_ready.message": "ход {turn} готов",
 	"game.events.turn_ready.action": "открыть",
 	"game.events.signature_failed": "подпись повреждена, переподключение…",
+	"game.events.unavailable.message": "эта игра больше недоступна",
 
 	"login.title": "вход в Galaxy",
 	"login.email_label": "электронная почта",
@@ -119,6 +120,7 @@ const ru: Record<keyof typeof en, string> = {
 	"game.shell.menu.theme_light": "светлая",
 	"game.shell.menu.theme_dark": "тёмная",
 	"game.shell.menu.language": "язык",
+	"game.shell.menu.return_to_lobby": "вернуться в лобби",
 	"game.shell.menu.logout": "выйти",
 	"game.shell.coming_soon": "скоро будет",
 	"game.shell.turn.label": "ход {turn}",