The Lambda takes the master, stores it in a private bucket, and renders a 30-second preview — or a watermarked image, or a two-page PDF — into the public one. Only the preview has a public URL.

Play, share, embed — the page only ever holds the short file. There is no full-length URL in the markup to find, because the page was never given one.

Buying one track mints a signed URL for that track only. Buying the album mints them all. The check is per item, never per release.

Every purchase is recorded against the item. That's what turns a Buy button into Download, and what takes the price off the album if you upgrade later.