M1/M2: engine + tyre audio, night-city ambience

SoundController (client):
- Looping engine sound on the car body: pitch 0.7->1.9 tracks speed
  (curved so low speed feels torquey), volume swells with throttle
- Tyre squeal loop faded by lateral slip (velocity along body RightVector)
  and hard braking from speed; always playing at 0 volume to avoid pops
- 3D sounds with rolloff so other players hear cars pass
- Asset IDs from safe sources (Roblox Resources engine loop,
  ProSoundEffects squeal); swap in SOUNDS table after audition

Ambience (server):
- Atmosphere (purple-grey haze, glare) so neon reads in the air
- BloomEffect for neon pop + subtle cool ColorCorrection
- Slow ClockTime ping-pong 22:00->03:00 over 10 min: always night,
  but the sky breathes

src/client/SoundController.luau

@@ -0,0 +1,161 @@
+--!strict
+--[[
+	SoundController.luau  (CLIENT)
+	Engine + tyre audio while the local player drives. Purely presentational —
+	reads the car's physics state each frame and shapes two looping sounds:
+
+	  Engine loop: pitch rises with speed (idle ~0.7 -> redline ~1.9), volume
+	    swells slightly with throttle. Cheap single-loop "engine", reads
+	    surprisingly well with the pitch curve.
+	  Tyre squeal: fades in when the car is sliding — lateral velocity across
+	    the body's right axis beyond a threshold (drift/hard corner/handbrake
+	    moments), or heavy braking while still moving.
+
+	Sounds attach to the car BODY (3D, rolloff), so other players' cars are
+	audible too when their sounds replicate — but this controller only shapes
+	the LOCAL car's sounds (we own its physics).
+
+	Asset notes (both from safe sources):
+	  - Engine: "Car-Engine-Loop" by Roblox Resources (official account)
+	  - Squeal: "Vehicle Skids Long Heavy Tire Squeal" by ProSoundEffects
+	    (Roblox's licensed SFX library)
+	Swap IDs freely in the SOUNDS table below if better loops are found.
+]]
+
+local Players = game:GetService("Players")
+local RunService = game:GetService("RunService")
+local ReplicatedStorage = game:GetService("ReplicatedStorage")
+
+local Shared = ReplicatedStorage.Shared
+local Cars = require(Shared.Cars)
+local Chassis = require(Shared.Chassis)
+
+local player = Players.LocalPlayer
+
+local SoundController = {}
+
+local SOUNDS = {
+	Engine = "rbxassetid://80317022777602",
+	Squeal = "rbxassetid://9120399077",
+}
+
+-- Tunables --------------------------------------------------------------------
+local ENGINE_MIN_PITCH = 0.7
+local ENGINE_MAX_PITCH = 1.9
+local ENGINE_BASE_VOLUME = 0.35
+local ENGINE_THROTTLE_SWELL = 0.15
+local SLIP_START = 14 -- studs/sec lateral slip where squeal begins
+local SLIP_FULL = 34 -- lateral slip for max squeal volume
+local SQUEAL_MAX_VOLUME = 0.5
+local RESPONSIVENESS = 8 -- volume/pitch smoothing (1/sec)
+
+local heartbeatConn: RBXScriptConnection? = nil
+local seatedConn: RBXScriptConnection? = nil
+local engineSound: Sound? = nil
+local squealSound: Sound? = nil
+
+local function smoothAlpha(k: number, dt: number): number
+	return 1 - math.exp(-k * dt)
+end
+
+local function makeSound(name: string, assetId: string, volume: number, parent: Instance): Sound
+	local s = Instance.new("Sound")
+	s.Name = name
+	s.SoundId = assetId
+	s.Looped = true
+	s.Volume = volume
+	s.RollOffMode = Enum.RollOffMode.InverseTapered
+	s.RollOffMinDistance = 15
+	s.RollOffMaxDistance = 220
+	s.Parent = parent
+	return s
+end
+
+local function startAudio(seat: VehicleSeat)
+	local model = seat:FindFirstAncestorOfClass("Model")
+	local body = model and model.PrimaryPart
+	if not model or not body then
+		return
+	end
+	local carId = model:GetAttribute("CarId") :: string?
+	local car = carId and Cars.Get(carId) or nil
+	if not car then
+		return
+	end
+	local tuning = Chassis.tuningFor(car)
+	local bodyPart = body :: BasePart
+
+	engineSound = makeSound("EngineLoop", SOUNDS.Engine, ENGINE_BASE_VOLUME, bodyPart)
+	squealSound = makeSound("TyreSqueal", SOUNDS.Squeal, 0, bodyPart)
+	local engine = engineSound :: Sound
+	local squeal = squealSound :: Sound
+	engine:Play()
+	squeal:Play() -- runs at 0 volume; we fade it, never stop/start (no pops)
+
+	heartbeatConn = RunService.Heartbeat:Connect(function(dt)
+		if not bodyPart.Parent then
+			return
+		end
+		local velocity = bodyPart.AssemblyLinearVelocity
+		local speed = velocity.Magnitude
+		local speedFrac = math.clamp(speed / tuning.MaxSpeed, 0, 1)
+
+		-- Engine: pitch from speed (slight curve so low speeds feel torquey),
+		-- volume swells with throttle input.
+		local pitchTarget = ENGINE_MIN_PITCH + (ENGINE_MAX_PITCH - ENGINE_MIN_PITCH) * (speedFrac ^ 0.8)
+		local volTarget = ENGINE_BASE_VOLUME + ENGINE_THROTTLE_SWELL * math.abs(seat.ThrottleFloat)
+		local a = smoothAlpha(RESPONSIVENESS, dt)
+		engine.PlaybackSpeed += (pitchTarget - engine.PlaybackSpeed) * a
+		engine.Volume += (volTarget - engine.Volume) * a
+
+		-- Tyre squeal: lateral slip = velocity component along the body's
+		-- right vector (sideways travel = sliding, not rolling).
+		local lateral = math.abs(velocity:Dot(bodyPart.CFrame.RightVector))
+		local slipFrac = math.clamp((lateral - SLIP_START) / (SLIP_FULL - SLIP_START), 0, 1)
+		-- Also squeal under hard braking from speed (throttle released fast).
+		local braking = (seat.ThrottleFloat == 0 and speed > tuning.MaxSpeed * 0.5) and 0.25 or 0
+		local squealTarget = math.max(slipFrac, braking) * SQUEAL_MAX_VOLUME
+		squeal.Volume += (squealTarget - squeal.Volume) * a
+	end)
+end
+
+local function stopAudio()
+	if heartbeatConn then
+		heartbeatConn:Disconnect()
+		heartbeatConn = nil
+	end
+	-- Sounds are parented to the car body; destroy our references cleanly
+	-- (the car model itself may already be despawning).
+	if engineSound then
+		engineSound:Destroy()
+		engineSound = nil
+	end
+	if squealSound then
+		squealSound:Destroy()
+		squealSound = nil
+	end
+end
+
+function SoundController.init()
+	local function onCharacter(character: Model)
+		local humanoid = character:WaitForChild("Humanoid") :: Humanoid
+		if seatedConn then
+			seatedConn:Disconnect()
+		end
+		seatedConn = humanoid:GetPropertyChangedSignal("SeatPart"):Connect(function()
+			stopAudio()
+			local seatPart = humanoid.SeatPart
+			if seatPart and seatPart:IsA("VehicleSeat") and seatPart.Name == Chassis.SEAT_NAME then
+				startAudio(seatPart)
+			end
+		end)
+		humanoid.Died:Connect(stopAudio)
+	end
+
+	if player.Character then
+		onCharacter(player.Character)
+	end
+	player.CharacterAdded:Connect(onCharacter)
+end
+
+return SoundController

src/client/init.client.luau

@@ -17,9 +17,11 @@ local Remotes = require(Shared.Remotes)
 local Cars = require(Shared.Cars)
 local ChassisController = require(script.ChassisController)
 local CameraController = require(script.CameraController)
+local SoundController = require(script.SoundController)
 
 ChassisController.init()
 CameraController.init()
+SoundController.init()
 
 local player = Players.LocalPlayer
 local playerGui = player:WaitForChild("PlayerGui")