The 'decider' is the system as a whole. The world and the environment and us, where how events - if deterministic - evolve from past to present and future states of the system.
This is just a verbose way of saying "people are part of the universe".
It does not follow that the universe
but not the person is the entity making a decision.
That’s the thing, and the question he keeps dodging, though he seems to imagine he answered it. What wrote the jazz score? What designed the great building? What wrote the great novel? The universe? the big bang? How did it do that? At last Jerry Coyne forthrightly said that the jazz score was not written by the jazz musician, and when he told him that, the musician got mad at him. And who can blame him?
That's not it at all. Not even close. Being a part of the universe does not equate to free will.
Acting according to one's will does not equate to free will. It does not equate to free will because will is related to action, where you may feel both the urge to indulge in something at the same time as the urge to refrain because it is harmful in some way.
What you guys dodge is that action production by a deterministic process is not a matter of free will.
That if the world is deterministic - and compatibilists are determinists - all actions are produced by deterministic processes, which includes everything that happens within a brain, where every thought decision and action is produced by a deterministic process that is not freely willed, therefore has nothing to do with free will.
That is the point at which compatibilism fails as an argument.