Artifact: Guardrail Metric Selection — Kestrel Checkout Speed

Guardrails chosen for a checkout-speed experiment -- exercises co-15. Kestrel is a fictional product; every quoted number, question, or finding here is an illustrative, constructed example, not real data or a real transcript.

Primary metric (OEC): checkout completion rate (% of teams that start the upgrade flow and finish it).

Guardrail 1 -- payment-failure rate: must not increase. A faster flow that rushes people past the payment-details step could increase mistyped card numbers or expiry dates, a cost the primary conversion metric alone wouldn't reveal (a failed payment still counts as "started checkout").

Guardrail 2 -- 48-hour refund-request rate: must not increase. A too-frictionless checkout risks buyer's-remorse upgrades -- a team that upgraded almost accidentally, without fully registering the commitment, showing up a day or two later asking to downgrade.