Stage 17 (#4): in-memory lobby cache — render instantly on the back-slide, refresh in background

ui/src/lib/app.svelte.ts

@@ -13,6 +13,7 @@ import { insideTelegram, onTelegramPath, telegramColorScheme, telegramLaunch, te
 import { parseStartParam } from './deeplink';
 import { clearSession, loadPrefs, loadSession, saveSession, savePrefs } from './session';
 import { clearGameCache } from './gamecache';
+import { clearLobby } from './lobbycache';
 import type { BoardLabelMode } from './boardlabels';
 
 export interface Toast {
@@ -311,6 +312,7 @@ export async function loginEmail(email: string, code: string): Promise<void> {
 export async function logout(): Promise<void> {
   closeStream();
   clearGameCache();
+  clearLobby();
   gateway.setToken(null);
   await clearSession();
   app.session = null;

ui/src/lib/lobbycache.ts

@@ -0,0 +1,30 @@
+// In-memory lobby snapshot, the lobby counterpart of gamecache.ts. The lobby re-fetches
+// its lists on every entry, so without a cache the screen renders blank and "draws in"
+// during the back-slide from a game. Caching the last lists lets the lobby render
+// instantly (before/under the transition) and refresh in the background. Process-memory
+// only; cleared on logout.
+
+import type { AccountRef, GameView, Invitation } from './model';
+
+interface LobbySnapshot {
+  games: GameView[];
+  invitations: Invitation[];
+  incoming: AccountRef[];
+}
+
+let snapshot: LobbySnapshot | null = null;
+
+/** getLobby returns the last lobby lists, or null before the first load. */
+export function getLobby(): LobbySnapshot | null {
+  return snapshot;
+}
+
+/** setLobby stores the latest lobby lists. */
+export function setLobby(s: LobbySnapshot): void {
+  snapshot = s;
+}
+
+/** clearLobby drops the cached lobby (called on logout). */
+export function clearLobby(): void {
+  snapshot = null;
+}