Know what changed.
Keep the uncertainty.

A price is not stock evidence.

Availability comes from explicit product flags or supplied variant flags. Missing values remain unknown. Only a known false → true transition is called a restock. A product absent from the next snapshot is “not observed,” not assumed sold out.

Prices retain their source currency. Sorting groups currencies before comparing numeric amounts; no exchange rate is invented. Snapshots are observations at capture time, not promises of present inventory or checkout availability.