Build configurable BlockParty minigame

Co-Authored-By: Claude Sonnet 5 <[email protected]>

src/main/java/us/tss3/blockparty/session/SessionManager.java

@@ -0,0 +1,31 @@
+package us.tss3.blockparty.session;
+
+import java.util.Map;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+
+/** Tracks which arena (if any) each online player is currently in. Enforces single-arena membership. */
+public class SessionManager {
+
+    private final Map<UUID, PlayerSession> sessions = new ConcurrentHashMap<>();
+
+    public boolean isInSession(UUID uuid) {
+        return sessions.containsKey(uuid);
+    }
+
+    public PlayerSession get(UUID uuid) {
+        return sessions.get(uuid);
+    }
+
+    public void add(PlayerSession session) {
+        sessions.put(session.getUuid(), session);
+    }
+
+    public void remove(UUID uuid) {
+        sessions.remove(uuid);
+    }
+
+    public Map<UUID, PlayerSession> all() {
+        return sessions;
+    }
+}