

That’s a transfer within the platform, very different from the scenarios I described. There is no method supported by GOG or Steam to transfer a game to a competing platform.
You can’t open a support case and tell them “sorry I actually wanted this game on GOG, can you transfer it to my account there?”. At best you could ask for a refund, obviously if you’ve played the game enough you wouldn’t even be able to ask for that.
Saying full source code leaked is a little wrong.
Plugin was always open source, and all plugins for that framework are required to be open source by the framework’s licensing.
Doesn’t change the fact that once one person did it, the code was available for anyone, though, you’re right.