fix(chat): don't restore unread on a failed read-ack (would loop the in-game effect; REST re-seed self-heals)

ui/src/lib/app.svelte.ts

@@ -166,14 +166,15 @@ export function seedChatUnread(gameId: string, unread: boolean): void {
  * markChatRead clears a game's unread badge and tells the backend the player has read the chat —
  * called when the move history or the chat opens. It hits the backend only when something is
  * actually unread, so opening the history does not call the backend on every tap. The clear is
- * optimistic; a failed ack restores the badge so a later open retries.
+ * optimistic and the ack is best-effort: a failed ack leaves the server bit set, which the next
+ * authoritative REST view (lobby list / game state) re-seeds, so the badge self-heals — it is
+ * deliberately not restored here, since the in-game effect re-runs while the history is shown and
+ * a restore would loop on a persistently failing ack.
  */
 export function markChatRead(gameId: string): void {
   if (!app.chatUnread[gameId]) return;
   app.chatUnread = { ...app.chatUnread, [gameId]: false };
-  void gateway.markChatRead(gameId).catch(() => {
+  void gateway.markChatRead(gameId).catch(() => {});
-    app.chatUnread = { ...app.chatUnread, [gameId]: true };
-  });
 }
 
 /** handleError maps a GatewayError to a toast; an invalid session logs out. A connectivity