How to make a Roblox checkpoint system (with AI)

Example output from a build like this

4 files in this example. Picoo writes this code for your prompt, so file names and sizes vary.

Sample output: ServerScriptService/CheckpointManager.lua

--!strict
-- ServerScriptService/CheckpointManager.lua  (Picoo · excerpt)
local Players = game:GetService("Players")
local CollectionService = game:GetService("CollectionService")
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local CheckpointHit = ReplicatedStorage:WaitForChild("Remotes"):WaitForChild("CheckpointHit")
local SaveService = require(script.Parent.CheckpointSaveService)

type State = { current: number, segmentStart: number }
local progress: { [Player]: State } = {}

local function setup()
    for _, part in ipairs(CollectionService:GetTagged("Checkpoint")) do
        local n = part:GetAttribute("CheckpointNumber") :: number
        if not n then continue end
        part.Touched:Connect(function(hit)
            local player = Players:GetPlayerFromCharacter(hit.Parent)
            if not player then return end
            local p = progress[player] or { current = 0, segmentStart = os.clock() }

            -- Sequence enforcement
            if n ~= p.current + 1 then return end

            local segmentTime = os.clock() - p.segmentStart
            p.current = n
            p.segmentStart = os.clock()
            progress[player] = p

            player.RespawnLocation = part
            SaveService:Set(player, p.current)
            CheckpointHit:FireClient(player, n, segmentTime)
        end)
    end
end

setup()