Initialize simulation as background task to fix WS timeout on Render

SemSorter/server/app.py

@@ -140,11 +140,16 @@ async def _simulation_tick_loop() -> None:
 
 @app.on_event("startup")
 async def startup():
-    global _main_loop, _frame_ready_event
+    global _main_loop, _frame_ready_event, _sim_tick_task
     _main_loop = asyncio.get_running_loop()
     _frame_ready_event = asyncio.Event()
     bridge.set_frame_ready_event(_main_loop, _frame_ready_event)
-    logger.info("Server ready (Simulation will load lazily on first connect)")
+    logger.info("Server ready. Backgrounding simulation initialization...")
+    
+    # Initialize the simulation asynchronously in the background so it doesn't block
+    # the main event loop and cause WS timeouts on low-CPU instances like Render Free Tier.
+    asyncio.create_task(bridge.run_in_sim_thread(bridge.get_simulation))
+    _sim_tick_task = asyncio.create_task(_simulation_tick_loop())
 
 
 @app.on_event("shutdown")
@@ -231,12 +236,6 @@ async def ws_chat(ws: WebSocket):
     _chat_clients.add(ws)
     logger.info("Chat client connected (%d total)", len(_chat_clients))
     
-    # Lazily start simulation if this is the first client
-    if _sim_tick_task is None:
-        logger.info("First client connected; starting MuJoCo simulation...")
-        await bridge.run_in_sim_thread(bridge.get_simulation)
-        _sim_tick_task = asyncio.create_task(_simulation_tick_loop())
-        
     try:
         await ws.send_text(json.dumps({
             "type": "welcome",
@@ -323,12 +322,6 @@ async def ws_video(ws: WebSocket):
     _video_clients.add(ws)
     logger.info("Video client connected")
     
-    # Lazily start simulation if this is the first client
-    if _sim_tick_task is None:
-        logger.info("First client connected; starting MuJoCo simulation...")
-        await bridge.run_in_sim_thread(bridge.get_simulation)
-        _sim_tick_task = asyncio.create_task(_simulation_tick_loop())
-        
     try:
         while True:
             # Wait for new frame (event-driven; sends exactly when sim produces one)