Add pregame lobby with live chat

Players used to get bounced back to the dashboard when a session
wasn't full yet. Now they land on a lobby page showing who has
joined, and can chat with each other while waiting - messages are
broadcast live over the existing Mercure hub, and the session
auto-starts (and the lobby notifies everyone) once it fills up.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/Game/Service/GameDashboardService.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 namespace App\Game\Service;
 
 use App\Game\Entity\Game;
+use App\Game\Entity\LobbyMessage;
 use App\Game\Entity\Player;
 use App\Game\Entity\Session;
 use App\Game\Entity\SessionSetting;
@@ -11,6 +12,7 @@ use App\Game\Enum\GameStatus;
 use App\Game\Enum\SessionSettingType;
 use App\Game\Enum\SessionStatus;
 use App\Game\Repository\GameRepository;
+use App\Game\Repository\LobbyMessageRepository;
 use App\Game\Repository\SessionRepository;
 use App\Tech\Entity\User;
 use Doctrine\ORM\EntityManagerInterface;
@@ -21,10 +23,12 @@ use Symfony\Component\Mercure\Update;
 final class GameDashboardService
 {
     private const READY_TIMEOUT_SECONDS = 60;
+    private const LOBBY_MESSAGE_MAX_LENGTH = 500;
 
     public function __construct(
         private readonly GameRepository $gameRepository,
         private readonly SessionRepository $sessionRepository,
+        private readonly LobbyMessageRepository $lobbyMessageRepository,
         private readonly EntityManagerInterface $entityManager,
         private readonly HubInterface $hub,
     ) {
@@ -122,6 +126,8 @@ final class GameDashboardService
 
         $this->entityManager->flush();
 
+        $this->publishLobbyEvent($session, 'player_joined');
+
         if (count($session->getPlayers()) === $session->getGame()->getNumberOfPlayers()) {
             $this->startSession($session);
         }
@@ -283,9 +289,60 @@ final class GameDashboardService
         $this->entityManager->persist($session);
         $this->entityManager->flush();
 
+        $this->publishLobbyEvent($session, 'session_started');
+
         return true;
     }
 
+    /**
+     * @return LobbyMessage[]
+     */
+    public function getLobbyMessages(Session $session): array
+    {
+        return $this->lobbyMessageRepository->findForSession($session);
+    }
+
+    public function postLobbyMessage(Session $session, User $user, string $content): ?LobbyMessage
+    {
+        if ($session->getStatus() !== SessionStatus::CREATED) {
+            return null;
+        }
+
+        $player = null;
+        foreach ($session->getPlayers() as $sessionPlayer) {
+            if ($sessionPlayer->getUser() === $user) {
+                $player = $sessionPlayer;
+                break;
+            }
+        }
+
+        if (!$player) {
+            return null;
+        }
+
+        $content = trim($content);
+        if ($content === '') {
+            return null;
+        }
+        $content = mb_substr($content, 0, self::LOBBY_MESSAGE_MAX_LENGTH);
+
+        $message = new LobbyMessage();
+        $message->setSession($session);
+        $message->setPlayer($player);
+        $message->setContent($content);
+
+        $this->entityManager->persist($message);
+        $this->entityManager->flush();
+
+        $this->publishLobbyEvent($session, 'lobby_message', [
+            'username' => $user->getUserIdentifier(),
+            'content' => $content,
+            'createdAt' => $message->getCreatedAt()->format(DATE_ATOM),
+        ]);
+
+        return $message;
+    }
+
     public function toggleReady(Session $session, User $user): bool
     {
         if ($session->getStatus() !== SessionStatus::READY) {
@@ -393,10 +450,15 @@ final class GameDashboardService
     }
 
     private function publishPlayerReady(Session $session, int $screen, bool $ready): void
+    {
+        $this->publishLobbyEvent($session, 'player_ready', ['player' => $screen, 'ready' => $ready]);
+    }
+
+    private function publishLobbyEvent(Session $session, string $type, array $extra = []): void
     {
         try {
             $topic = '/game/hub/' . $session->getId();
-            $this->hub->publish(new Update($topic, json_encode(['type' => 'player_ready', 'player' => $screen, 'ready' => $ready])));
+            $this->hub->publish(new Update($topic, json_encode(array_merge(['type' => $type], $extra))));
         } catch (\Exception $e) {
             // Mercure might be down, but we don't want to crash the game
         }