launcher-builder should probably warn (or perhaps error) if one accidentally includes two different versions of forge

[miiichael]

Because not everyone will know straight away what "Found multiple arguments for option launchTarget, but you asked for only one" means. 😅

[hedgehog1029]

Ideally I'd report incompatibilities in general... Forge and LiteLoader are compatible but Fabric and Forge are not, for example. And I need a way of resolving which main class should be used, really.