Developers

Cairn is a Unity IL2CPP game. Mods are .NET assemblies: MelonLoader loads them, Il2CppInterop exposes the game types, Harmony patches them.

Stack

MelonLoader — loads mod assemblies, lifecycle hooks
Il2CppInterop — managed proxies; call Il2Cpp.<Type>
Harmony — prefix / postfix the game's own methods

Build on the libraries

CairnAPI lib Shared C# layer the other mods build on.

The cross-menu toolkit (formerly CrossMenuLib) is folding into CairnAPI — target that.

Minimal mod

using MelonLoader;

[assembly: MelonInfo(typeof(MyMod.Core), "MyMod", "0.1.0", "you")]
[assembly: MelonGame("The Game Bakers", "Cairn")]

namespace MyMod;

public class Core : MelonMod
{
    public override void OnInitializeMelon() => LoggerInstance.Msg("loaded");
    public override void OnUpdate() { /* per-frame */ }
}

Build against MelonLoader\Il2CppAssemblies\ (generated on first run), reference MelonLoader.dll, drop the .dll in Mods\.

Live iteration

CairnDevTools runs an HTTP console that evals C# against the live game — probe state without a rebuild.