Response headers
x-fuse-request-idmatches the row in the project log.x-fuse-reserved-usdis the worst-case hold taken before the provider was called.x-fuse-cost-usdis set when the final cost is known.
After a request is forwarded, the provider status and body are returned as the provider sent them.
Refusals from Fuse use the same x-fuse-request-id. Look that id up in the project log. x-fuse-reserved-usd is present on the way out, before usage is known. x-fuse-cost-usd replaces the estimate when the provider usage has been read. On a refusal before any provider call, there is no cost header, because nothing was reserved or the reservation was not a completed call.
Do not parse the provider body to discover the Fuse decision. Use the HTTP status and the error field. Provider errors keep the provider's own JSON shape.