composing-a-policy-layer

Composing a policy layer

A policy engine answers one question about a proposed agent action: does it proceed or not. Amount caps, allowlists, rate limits, sanctions screening, a human in the loop gate. This is real and useful work, and it sits next to the ERC stack rather than inside it. This skill is about wiring one in without dissolving the guarantees the stack is built on.

The subject here is any external policy engine. Bastion and CAPV appear once, at the end, as a concrete worked example, not as the point.

The one rule to internalize first

The verifier decides validity. The policy engine decides whether to proceed. These are different questions and they must stay in different components.

A policy layer that also starts deciding what an ERC record means, whether an inference proof is good, or whether an action should be anchored has stopped composing and started wrapping. Wrapping feels tidy because one object now speaks for the whole flow, but it inherits every breaking change in every ERC it speaks for, and it moves the trust boundary back onto itself. The whole reason the stack exists is that a reader does not have to trust any one component. A policy layer that swallows the primitives quietly undoes that.

1. Where a policy layer sits

Beside the primitives, on the path, gating the transition. Not above them, not translating them.

ERC-8004 identity        proposed action        ERC-8263 anchor
    (who)          ->        (what)        ->      (recorded)
                               |
                         Policy Guard
                     (proceed or do not)
                               |
                       ERC-8274 verify
                       (inference proof)

The identity registry still says who the actor is. The verifier still says whether a proof is valid. The anchor still records the timeline. The policy Guard reads what it needs from those and returns a single verdict on whether this action is allowed to continue. It does not re-answer any of their questions.