An agent must come to a decision about a specific action fast enough to actually make that action. This runtime limitation doesn't seem to be so different from any other influence of the choice of the algorithm on the outcome, and it also doesn't seem in any way simple, so granting that no other limitation of the algorithm is present doesn't seem to significantly simplify the problem. Algorithm is part of policy, if not all of it.

An agent can be treated as generalization of action, and the algorithm part as a notion of externalized computation. Using agents corresponds to distributing computation of decisions over time and space, allowing the actions (or possible actions) to finish up the computation.

Why design CSAs at all, rather than look-up tables or non-agent-like jumbles of wires?

I don't see a salient distinction. Agent is one kind of jumble of wires. It is a highly compressed representation of what is denotationally equivalent to a look-up table. Agent with a nice decision theory is presumably a theory of how to do general-purpose design of good jumbles of wires.