A button's radius, a card's shadow, the exact grey of a disabled state — these are brand decisions that happen to be written in code. When the system is owned only by engineering, those decisions get made by whoever is closest to the ticket.
We build the system as a shared artefact. Design owns the tokens and the intent; engineering owns the implementation and the guarantees. Neither ships a new pattern alone.
The payoff is boring on purpose: every screen looks like it came from the same place, because it did.