Repair Cancellation Propagation

Our Next.js/TypeScript API uses AbortController at the route layer, but the signal is not passed through the service to our fetch-based vendor client or Prisma wrapper. When a browser cancels a long export request, the vendor call and database aggregation continue for 20–40 seconds. Promise.all starts four child operations; if one fails, two others keep running. A retry helper can start another vendor request even after the route was cancelled. Repair cancellation propagation locally with deterministic tests. Do not call the live vendor, query production data, kill production jobs, or assume an already accepted vendor request was undone by local cancellation.

Cancellation propagation gaps found. The request AbortSignal is lost at service boundaries, vendor calls ignore it, sibling work can outlive failure, and retry may start after cancellation. The repair forwards cancellation through request-owned work, adds structured cleanup and retry suppression, protects durable handoff boundaries, and adds deterministic cancellation tests. Remote provider and production DB cancellation remain unverified.