Refactor: Add LobbyCleanupJob for periodic expired lobby cleanup

- isolate failures per lobby during cleanup
- notify connected sessions about closed lobbies
Refs #124

Co-authored-by: Copilot <copilot@github.com>

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/lobby/LobbyCleanupJob.java

@@ -0,0 +1,100 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.SuccessResponse;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.builder.ResponseBody;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatcher;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.Session;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionManager;
+import java.time.Duration;
+import java.util.List;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+/** Periodically removes expired empty lobbies and notifies connected sessions. */
+public class LobbyCleanupJob implements Runnable {
+
+    private static final Logger LOGGER = LogManager.getLogger(LobbyCleanupJob.class);
+
+    private final LobbyManager lobbyManager;
+    private final SessionManager sessionManager;
+    private final ResponseDispatcher responseDispatcher;
+    private final Duration expiryThreshold;
+
+    /**
+     * Creates a new cleanup job for expired empty lobbies.
+     *
+     * @param lobbyManager manager used to find and remove expired lobbies
+     * @param sessionManager manager used to resolve connected sessions
+     * @param responseDispatcher dispatcher used to notify clients about closed lobbies
+     * @param expiryThreshold age threshold that marks an empty lobby as expired
+     */
+    public LobbyCleanupJob(
+            LobbyManager lobbyManager,
+            SessionManager sessionManager,
+            ResponseDispatcher responseDispatcher,
+            Duration expiryThreshold) {
+        this.lobbyManager = lobbyManager;
+        this.sessionManager = sessionManager;
+        this.responseDispatcher = responseDispatcher;
+        this.expiryThreshold = expiryThreshold;
+    }
+
+    /**
+     * Runs one cleanup cycle.
+     *
+     * <p>The method first fetches all expired empty lobbies. Each lobby is then processed
+     * independently so that a failure for one lobby does not stop the remaining cleanups.
+     */
+    @Override
+    public void run() {
+        LOGGER.debug("Job started.");
+        try {
+            List<LobbyId> expired;
+            try {
+                expired = lobbyManager.findEmptyLobbiesOlderThan(expiryThreshold);
+            } catch (Exception e) {
+                LOGGER.error("Lobby expiry job failed: could not fetch expired lobbies", e);
+                return;
+            }
+
+            for (LobbyId lobbyId : expired) {
+                try {
+                    lobbyManager.removeLobby(lobbyId);
+                    broadcastLobbyClosed(lobbyId);
+                } catch (RuntimeException e) {
+                    LOGGER.warn("Failed to process expired lobby {}", lobbyId.value(), e);
+                }
+            }
+        } finally {
+            LOGGER.debug("Job finished.");
+        }
+    }
+
+    /**
+     * Broadcasts a lobby-closed event to all currently connected sessions.
+     *
+     * @param lobbyId id of the lobby that was closed
+     */
+    private void broadcastLobbyClosed(LobbyId lobbyId) {
+        for (Session session : sessionManager.getAllSessions()) {
+            try {
+                RequestContext ctx = new RequestContext(session.getId(), 0);
+                SuccessResponse event =
+                        new SuccessResponse(
+                                ctx,
+                                ResponseBody.builder()
+                                        .param("EVENT", "LOBBY_CLOSED")
+                                        .param("LOBBY_ID", lobbyId.value())
+                                        .build()) {};
+                responseDispatcher.dispatch(event);
+            } catch (RuntimeException e) {
+                LOGGER.warn(
+                        "Failed to notify session {} about closed lobby {}",
+                        session.getId().value(),
+                        lobbyId.value(),
+                        e);
+            }
+        }
+    }
+}