make-sauth-game

name	make_sauth_game
description	Scaffold a new server-authoritative (SA) custom physics character game for Roblox from an empty baseplate — place settings, the four-file spawn/input/sim/client architecture, and playtest checkpoints. Use when the user wants to start a new SA physics game or invokes /make_sauth_game.

Make a server-authoritative physics game

Scaffold a working SA physics character from verified templates in this repo. The output is a character you can drive with WASD, camera-relative, predicted on the owning client, before any game-specific features.

This file is a procedure, not doctrine. The rules live in docs/reference/ and are maintained there. Do not copy them back into this file — a second copy drifts, and has already done so twice. Link instead.

0. Read the rules first

Read docs/reference/rules.md before writing any code. It is ~1,400 words and it is the whole set of invariants, the banned-inside-the-sim table, and the silent-failure table.

Almost every Server Authority failure mode is silent. No error, no warning, no output — just a character that feels laggy, or does not move, or mispredicts constantly. You cannot debug your way to these; you have to not make them. That is what the tables are for.

Keep patterns.md open for the code shapes.

1. Gather the concept (ask once, briefly)

• Character name and rough body plan (root part + what hangs off it).
• Where the synced script folder lives (ScriptSync root).

Default to a two-part rig — one dense root part plus one light part on a loose ball socket — if the user has no strong opinion. It proves every pipeline stage and is trivially reshaped later.

2. Place settings

These are place state, not code. AuthorityMode cannot be read or written from tooling Luau (a script that tries gets lacking capability RobloxScript), so the user must do it by hand:

1. Workspace.AuthorityMode = Server in the Properties panel.
2. Untick Players.CharacterAutoLoads.
3. Save the place file.

The server script also sets Players.CharacterAutoLoads = false in code so the assumption is visible in source control. Either alone is enough; do both.

No Humanoids, ever.

3. Generate the four files

Scaffold from the cube set. It is ~200 lines, has no rig complexity, and is verified line-for-line against Chapter 1 of the tutorial:

Template	Class	Role
samples/cube/ServerScriptService/CubeServer.legacy.luau	Script	Place settings, spawning, actuators, InputContext
samples/cube/ReplicatedFirst/CubeSim.luau	ModuleScript	The shared brain — velocity servo + steering
samples/cube/ReplicatedFirst/CubeClient.local.luau	LocalScript	Prediction bootstrap, camera, CameraDir feed
samples/cube/ReplicatedFirst/CubePresent.luau	ModuleScript	Presentation layer + the critically-damped spring

Rename Cube* to the user's character. Keep the file-class suffixes: .luau ModuleScript, .local.luau LocalScript, .legacy.luau Script.

The CakeMan set at the repo root (ReplicatedFirst/CakeSim.luau, ReplicatedFirst/Presentation.luau, ReplicatedFirst/Smoothing.luau, ServerScriptService/CakeServer.legacy.luau, ServerScriptService/CakePunch.legacy.luau, ServerStorage/GenerateRig.legacy.luau) is the next step, not the scaffold — a ball-socket ragdoll with a rig generator and a punch mechanic. Reach for it once the cube drives.

4. Scaffold decisions you have to make explicitly

Everything else is skinnable; these are the choices the templates encode that an adaptation can silently get wrong. Each links to the reasoning.

• ModelStreamingMode — the cube uses Persistent. An instance the client was never sent cannot be predicted, which makes Persistent the stronger guarantee for a character; Atomic only promises you never see half a model. → patterns.md §15
• Bind frequency — pass Enum.StepFrequency.Hz60. The default is Hz30 while physics runs at 60, so the servo corrects half as often as the world it is correcting. → rules.md #2
• Both sides initialize the sim module — the server Script and the client LocalScript each require and Initialize() the same file. Miss one and nothing moves, with no error. → rules.md #1
• Tunables at the top of the sim file, in acceleration units, each with a comment saying what it feels like. Knobs then keep their meaning when the rig's mass changes. → physics-characters.md §2

5. Verify — checkpoint before features

Run single-process Play. It runs the real predict/resimulate loop and is accurate for building and tuning. Switch to Test → Server & Clients (1 client) plus Network Simulation when you specifically want behavior under real latency.

1. Character spawns, console clean.
2. RunService:GetPredictionStatus(root) returns Enum.PredictionStatus.Predicted. If it says Authoritative, a character part is anchored.
3. WASD drives it camera-relative; holding W while swinging the camera carves a curve.
4. Speed rises to ~TARGET_SPEED and holds. Trace it — numbers, not vibes:

-- client command bar, while driving
local root = workspace.<Folder>["<Name>_" .. game.Players.LocalPlayer.UserId].<Root>
task.spawn(function()
	for _ = 1, 10 do
		local v = root.AssemblyLinearVelocity
		print(string.format("v=%.1f", (v - Vector3.yAxis * v.Y).Magnitude))
		task.wait(0.5)
	end
end)

Scaffold-stage symptoms. The full 19-row table is rules.md:

Symptom	Cause
Nothing moves	Sim module not initialized on both sides
Input feels like full round-trip lag	player.Character not set — that is what pulls parts into the prediction loop
Character never rolls back, status Authoritative	A character part is Anchored
Stock camera pushes through the character	player.Character not set
Camera sits near the world origin	No PlayerModule in a characterless place — build it, and set CameraType = Scriptable
Steering ignores the camera	CameraDir action not firing, or the sim reads the camera directly
Accelerates forever / overshoots	Velocity set directly, or the negative gap term was dropped
An action does nothing	The InputAction has no .Name
Constant jitter/rubber-banding	A real prediction bug — chase it, don't switch test modes

6. What comes next (point, don't build)

Wobble mass, gait and feet, and the presentation layer. Follow the chapter order in docs/ rather than improvising it.

For anything past the scaffold — omni-surface traversal, gait, chains, steering math, feel tuning — physics-characters.md has the doctrine and the measurements behind it.