Post-payment action gap: settlement tx proves payment, not what the agent did with the data

The example closes cleanly at settlement — `txHash` lands in the response, Arbiscan link included. That proves the agent paid for access to `premium-market-data`.

It doesn't prove what the agent did with `{ btc: 71234.56, eth: 4567.89 }` after receiving it.

Your piece on the agent economy verification problem frames the inference layer — whether the model ran what it claimed. This is the layer above: whether the agent took the action it was authorized to take with the data it paid for. In automated trading, multi-agent pipelines, or any context where downstream decisions are auditable, that's the record regulators and auditors actually need.

The gap is visible in `server.ts` at `premiumContent()` — `requestId: crypto.randomUUID()` identifies the response but isn't anchored anywhere a third party can reference later. The buyer address and payment intent are already present in the verified `paymentPayload`; a post-settlement action record could derive from them directly:

```ts
const action_ref = sha256(jcs({
agent_id: /* buyer address from verified paymentPayload */,
action_type: "fetch.premium-market-data",
scope: resourceUrl,
timestamp: new Date().toISOString(),
}));
```

Anchored alongside `txHash`, the receipt proves both: payment settled on Arbitrum + this specific agent took this specific action with the data — independently recomputable without trusting the operator.

A worked fixture for the x402 flow is at `giskard09/argentum-core/examples/conformance/` — the spec is `draft-giskard-aeoess-action-ref` (IETF). Live trails at `argentum.rgiskard.xyz/trails`.

Read server.ts at premiumContent() first, tracing the verified paymentPayload, txHash, and requestId flow; then compare the worked x402 fixture in giskard09/argentum-core/examples/conformance/ with draft-giskard-aeoess-action-ref. Done means the post-settlement action record is anchored alongside txHash and can be independently recomputed for the paid data action.

Written by the indexing model from the issue text.