Live game economies look chaotic from the outside. Underneath they are usually a short list of multipliers applied in a fixed order. The engineering problem is not how to win the game. It is how you encode the sell formula so a client-side tool stays honest after patches, refuses illegal stacks, and does not silently invent value. This walkthrough uses a compact JavaScript model for a Roblox farming sequel: a power-law weight term, a single mutation seat, a harvest-type keep rule, friend and ...