Project-M/Assets/_Project/Scripts/Client/UI/PauseMenuSystem.cs

using Unity.Entities;
using Unity.NetCode;
using UnityEngine;

namespace ProjectM.Client
{
    /// <summary>
    /// Client-only bootstrap that ensures the in-game pause overlay (Esc) exists once a session is running.
    /// Mirrors how HudSystem creates its UI at runtime — spawns one <see cref="PauseMenuController"/> GameObject
    /// in the active (Game) scene; the scene swap on Quit-to-Menu destroys it, and a fresh session's new client
    /// world spawns a new one. Client world only, so the menu's plain default world never spawns a pause overlay.
    /// </summary>
    [WorldSystemFilter(WorldSystemFilterFlags.ClientSimulation)]
    [UpdateInGroup(typeof(PresentationSystemGroup))]
    public partial class PauseMenuSystem : SystemBase
    {
        bool _spawned;

        protected override void OnUpdate()
        {
            if (_spawned) return;
            _spawned = true;
            new GameObject("~PauseMenu").AddComponent<PauseMenuController>();
        }
    }
}