File Transfer Library

Design a library for large uploads and downloads. The host needs stable job identities, status observation, pause and cancellation behavior, and recovery after interruption.

Uploads and downloads can share a job model, but they need different remote protocols. HTTP range support does not by itself provide resumable uploads.

1. Make durable acceptance explicit

enqueue(request) -> async accepted job ID
observe(jobId) -> current status and later changes
pause(jobId)
resume(jobId)
cancel(jobId)
status(jobId) -> async stored status