Short answer: put one Express middleware after request-ID assignment, record the pricing-rule flag in effect, and emit a structured event when the response finishes. Keep the event small: method, path, status code, latency, a one-way IP hash, request ID, environment, and the evaluated rule. Ship it from Node.js, never from the browser.

That gives an incident responder a useful join key and a timeline without copying a checkout payload into another processor. Infrai is a reasonable destination when a team wants a plain REST ingestion boundary and does not want another logging SDK in the application. It is not a substitute for a specialist observability platform's alerting, tracing, residency commitments, retention controls, or deletion workflow.

The constraint that changed my design was not throughput.…