Feature: Implement game initialization on startup and add "New Game" button to UI

api.py

@@ -17,6 +17,23 @@ app.add_middleware(
 engine: Engine | None = None
 
 
+@app.on_event("startup")
+async def _seed_default_game():
+    """Pre-create a game so visitors see a live arena instead of a lobby."""
+    global engine
+    try:
+        cfg = GameConfig(grid_size=20, max_turns=100, max_agents=4, num_chests=15)
+        eng = Engine(config=cfg)
+        eng.generate_grid()
+        eng.scatter_chests()
+        for i, name in enumerate(_default_names(4)):
+            eng.spawn_agent(agent_id=f"agent_{i}", name=name)
+        engine = eng
+    except Exception as exc:
+        import logging
+        logging.getLogger("uvicorn.error").warning(f"Default game seed failed: {exc}")
+
+
 class StartGameRequest(BaseModel):
     grid_size: int = 20
     max_turns: int = 50

frontend/static/index.html

@@ -1187,6 +1187,7 @@ body {
     </div>
 
     <div class="top-right">
+      <button class="camera-mode-badge" id="newGameBtn" onclick="returnToLobby()" title="Open lobby to start a new game">⚙ NEW GAME</button>
       <button class="camera-mode-badge" id="cameraModeBadge" onclick="togglePov()" title="Toggle chase cam (V) — select an agent first" disabled>📹 OVERVIEW</button>
       <span class="winner-announce" id="winnerAnnounce"></span>
     </div>
@@ -3072,6 +3073,37 @@ document.addEventListener('keydown', e => {
 });
 
 window.addEventListener('resize', ()=>{ if (app) app.resize(); });
+
+function returnToLobby() {
+  if (autoRunning) auto();
+  gameStarted = false; selectedId = null; state = null;
+  document.getElementById('lobby').classList.remove('hidden');
+  const g = document.getElementById('game'); g.classList.remove('visible'); g.style.display = 'none';
+}
+
+async function bootProbe() {
+  try {
+    const r = await fetch('/api/game/state');
+    if (!r.ok) return;
+    const s = await r.json();
+    if (!s || !s.agents || !s.agents.length) return;
+    state = s;
+    gameStarted = true;
+    nameMaterialCache = {};
+    traceHistory = {};
+    document.getElementById('lobby').classList.add('hidden');
+    const game = document.getElementById('game');
+    game.classList.add('visible'); game.style.display = 'flex';
+    showLoading('Joining live arena...');
+    try {
+      await loadThree();
+      if (!app) initScene();
+      requestAnimationFrame(() => { if (app) app.resize(); renderScene(); });
+      updateUI();
+    } finally { hideLoading(); }
+  } catch (_) { /* keep lobby */ }
+}
+bootProbe();
 </script>
 </body>
 </html>