Direct supplier costs include model inference, embeddings, reranking, speech, image or video generation, search, data enrichment, messaging, payment processing, and any metered external tool. Runtime costs can include cloud compute, databases, queues, object storage, logging, and network egress. Each event should identify the supplier, service, account or project when available, pricing basis, measured quantity, currency, and pricing-version reference. This detail is necessary when one workflow spans several vendors or when a provider changes a rate.
Not every infrastructure cost can be attached to one action with perfect causality. Shared databases, reserved capacity, and long-lived services often require an allocation policy. Label allocated costs as allocated, identify the denominator, and keep the policy version with the result. A reasonable allocation can guide decisions even when it is not an invoice-level charge. The mistake is presenting an allocation as a directly observed supplier amount or silently changing the method between reporting periods.