CanMoveItem

using System.Linq;
using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using Oxide.Core;
using UnityEngine;

namespace Oxide.Plugins
{
    [Info("Belt Item Restriction", "RustPluginGenerator", "1.0.0")]
    [Description("Blocks configured items from being moved into a player's belt container")]
    public class BeltItemRestriction : RustPlugin
    {
        private const string PermBypass = "beltitemrestriction.bypass";

        private PluginConfig config;
        private HashSet<string> blockedShortnames;

        private class PluginConfig
        {
            [JsonProperty("Blocked item shortnames")]
            public List<string> BlockedShortnames = new List<string> { "rocket.launcher", "explosive.satchel", "explosive.timed" };
        }

        protected override void LoadDefaultConfig() => config = new PluginConfig();

        protected override void LoadConfig()
        {
            base.LoadConfig();
            try
            {
                config = Config.ReadObject<PluginConfig>();
                if (config == null) throw new Exception();
            }
            catch
            {
                PrintWarning("Configuration file is invalid, using defaults");
                LoadDefaultConfig();
            }
            SaveConfig();
        }

        protected override void SaveConfig() => Config.WriteObject(config);

        protected override void LoadDefaultMessages()
        {
            lang.RegisterMessages(new Dictionary<string, string>
            {
                ["Blocked"] = "You cannot place {0} in your belt."
            }, this);
        }

        private string Msg(string key, string userId = null, params object[] args) => string.Format(lang.GetMessage(key, this, userId), args);

        private void Init()
        {
            permission.RegisterPermission(PermBypass, this);
            blockedShortnames = new HashSet<string>(config.BlockedShortnames, StringComparer.OrdinalIgnoreCase);
        }

        private object CanMoveItem(Item item, PlayerInventory playerInventory, ItemContainerId itemContainerId, int targetPosition, int amount, ItemMoveModifier itemMoveModifier)
        {
            if (item?.info == null || playerInventory?.containerBelt == null) return null;
            if (!blockedShortnames.Contains(item.info.shortname)) return null;
            if (itemContainerId.Value != playerInventory.containerBelt.uid.Value) return null;

            BasePlayer player = playerInventory.containerBelt.playerOwner;
            if (player == null || player.IsAdmin) return null;
            if (permission.UserHasPermission(player.UserIDString, PermBypass)) return null;

            player.ChatMessage(Msg("Blocked", player.UserIDString, item.info.displayName.english));
            return true;
        }
    }
}