Like /generateDownloadUrl, but a multi-image ORIGINAL download is queued to the shared-zip Lambda and returned as {status: "queued", parts: [{jobId, filename, ...}]} for the client to poll at /downloadJobStatus/{jobId}. See auxiliary/app_download_jobs.py for why.

Single images and reduced sizes still answer inline with {downloadUrl, filename, isZip}: a single image is only a presigned URL, and the worker only packages originals. Same inline answer when the queue is not configured (local dev).

A new endpoint rather than a new response shape on /generateDownloadUrl, so a browser still running the previous frontend bundle keeps getting the {downloadUrl} it understands.