Universal hitbox npc

-- NPC Hitbox Expander GUI — Works with most damage tools
-- Modes:
--  - Proxy: Adds a welded neon-red hitbox part (CanTouch/CanQuery = true) so weapons and raycasts register.
--  - Resize: Resizes the real HRP, optionally tints neon red. Reverts cleanly on disable.
-- Default size: 9, transparency: 0.4, mode: Proxy

--// Services
local Players = game:GetService("Players")
local UserInputService = game:GetService("UserInputService")
local CoreGui = game:GetService("CoreGui")

--// Constants
local GUI_NAME = "NPC_Hitbox_GUI"
local PROXY_NAME = "NF_NPC_Hitbox"
local TAG_ATTR = "NF_HitboxTag"
local MODE_PROXY, MODE_RESIZE = "Proxy", "Resize"

--// Cleanup previous UI
local old = CoreGui:FindFirstChild(GUI_NAME)
if old then old:Destroy() end

--// State
local enabled = false
local currentSize = 9
local currentTransparency = 0.40
local mode = MODE_PROXY

--// Helpers
local function isNPC(model)
    if not (model and model:IsA("Model")) then return false end
    local hum = model:FindFirstChildOfClass("Humanoid")
    if not hum then return false end
    return Players:GetPlayerFromCharacter(model) == nil
end

local function getRoot(model)
    if not model then return nil end
    return model:FindFirstChild("HumanoidRootPart")
        or model:FindFirstChild("UpperTorso")
        or model:FindFirstChild("Torso")