fix(ui): also resync an open game on a foreground regain without a stream drop

Closes the residual tail of the previous commit: when the live stream stays
alive across a brief suspend (Telegram/iOS can pause the socket without tearing
it down), an in-game event shed from a full hub buffer is never recovered by
the reconnect refetch (no reconnect) or the open-game poll (it only runs while
the stream is down). Mirror the lobby's focus re-poll: bump app.resync on a
foreground regain that did not drop the stream, and have Game.svelte refetch
the open game once per resync. Also rescues a missed move/game_over after a
suspend. Add a silent-join mock seam + an e2e isolating this path; extend the
ARCHITECTURE §10 fallback note.

ui/src/game/Game.svelte

@@ -263,6 +263,17 @@
     return () => clearInterval(timer);
   });
 
+  // (C) Returning to the foreground without the stream having dropped (so (A) does not fire) may
+  // still have missed an event shed from a full hub buffer while suspended; refetch once per resync.
+  let lastResync = app.resync;
+  $effect(() => {
+    const r = app.resync;
+    if (r !== lastResync) {
+      lastResync = r;
+      void load();
+    }
+  });
+
   function isCoarse(): boolean {
     return typeof matchMedia !== 'undefined' && matchMedia('(pointer: coarse)').matches;
   }

ui/src/lib/app.svelte.ts

@@ -55,6 +55,10 @@ export const app = $state<{
   notifications: number;
   /** Unread chat-message count per game id, for the in-game score-bar and 💬 badges. */
   chatUnread: Record<string, number>;
+  /** Monotonic counter bumped when the app returns to the foreground without the live stream
+   *  having dropped. An open game watches it to refetch once, recovering an in-game event shed
+   *  from a full hub buffer while suspended (the stream-drop case is covered by streamAlive). */
+  resync: number;
 }>({
   ready: false,
   streamAlive: false,
@@ -70,6 +74,7 @@ export const app = $state<{
   localeLocked: false,
   notifications: 0,
   chatUnread: {},
+  resync: 0,
 });
 
 let unsubscribeStream: (() => void) | null = null;
@@ -104,7 +109,13 @@ function goForeground(): void {
   backgrounded = false;
   foregroundedAt = Date.now();
   if (!app.session) return;
-  if (!app.streamAlive) openStream(); // silently re-establish a stream dropped while away
+  if (!app.streamAlive) {
+    openStream(); // re-establish a stream dropped while away (its reconnect refetch then runs)
+  } else {
+    // The stream stayed alive across the suspend, so the reconnect refetch will not fire — but an
+    // event may have been shed from a full hub buffer while away; nudge an open game to refetch.
+    app.resync++;
+  }
   void refreshNotifications();
 }
 

ui/src/lib/gateway.ts

@@ -22,7 +22,8 @@ if (isMock && typeof window !== 'undefined') {
   };
   // Drive the auto-match opponent join deterministically from the e2e (the mock otherwise
   // attaches a robot on a timer).
-  (window as unknown as { __mock?: { joinOpponent(): void } }).__mock = {
+  (window as unknown as { __mock?: { joinOpponent(): void; joinOpponentSilently(): void } }).__mock = {
     joinOpponent: () => (gateway as MockGateway).joinPendingOpponent(),
+    joinOpponentSilently: () => (gateway as MockGateway).joinPendingOpponentSilently(),
   };
 }

ui/src/lib/mock/client.ts

@@ -181,14 +181,22 @@ export class MockGateway implements GatewayClient {
     return { matched: false, game: structuredClone(g.view) };
   }
 
+  // seatOpponent seats a robot in an open game's empty seat and returns the game (null once it is no
+  // longer open). Shared by the live join (which then pushes opponent_joined) and the silent e2e
+  // variant (which omits the push).
+  private seatOpponent(id: string): MockGame | null {
+    const game = this.games.get(id);
+    if (!game || game.view.status !== 'open') return null;
+    game.view.status = 'active';
+    game.view.seats[1] = { seat: 1, accountId: 'robot', displayName: 'Robo', score: 0, hintsUsed: 0, isWinner: false };
+    return game;
+  }
+
   // fillOpponent seats a robot in an open game's empty seat and pushes opponent_joined — the
   // mock of a human or robot taking the seat. A no-op once the game is no longer open.
   private fillOpponent(id: string): void {
-    const game = this.games.get(id);
-    if (!game || game.view.status !== 'open') return;
-    game.view.status = 'active';
-    game.view.seats[1] = { seat: 1, accountId: 'robot', displayName: 'Robo', score: 0, hintsUsed: 0, isWinner: false };
-    this.emit({ kind: 'opponent_joined', gameId: id, state: this.stateOf(game) });
+    const game = this.seatOpponent(id);
+    if (game) this.emit({ kind: 'opponent_joined', gameId: id, state: this.stateOf(game) });
   }
 
   // joinPendingOpponent is the e2e hook (exposed as window.__mock.joinOpponent) to attach the
@@ -198,6 +206,13 @@ export class MockGateway implements GatewayClient {
     if (this.openGameId) this.fillOpponent(this.openGameId);
   }
 
+  // joinPendingOpponentSilently seats the opponent WITHOUT pushing opponent_joined — the mock of an
+  // event shed from a full hub buffer while the stream is alive, so the UI recovers only on a
+  // foreground resync. e2e hook: window.__mock.joinOpponentSilently.
+  joinPendingOpponentSilently(): void {
+    if (this.openGameId) this.seatOpponent(this.openGameId);
+  }
+
   async lobbyPoll(): Promise<MatchResult> {
     if (this.pendingMatch) {
       const g = this.games.get(this.pendingMatch);