I don't think Melody requires A3 to function any more, even though it's just A3's body with a new head.

It used to require RTEncoder. It no longer does, but they didn't change the readme.

Picture me firing up RTEncoder, trying to remember how it works, and scouring my runtime for the .rte file.

There wasn't one. Though the documentation says you need RTEncoder, and includes instructions on how to use it, you just install it like you would any other figure. It's not encoded at all.