Get Alert Matches

The NEW arrivals recorded against this alert — not everything on the site that happens to fit it — one page at a time, unseen ones first.

This deliberately reads alert_matches rather than re-querying car_listings. An alert answers "what showed up since I asked?", so a listing only appears here once a sync has brought it in and a matcher has recorded it against this alert; the full standing inventory is one click away behind the search page's own filters ("Ver na busca" in the UI), newest listings first.

A freshly-created alert is therefore empty until the next sync runs, which is intended — the empty state says so.

LIFETIME: a match stays until the user has seen it, at most 7 days from matched_at (expires_at, set at insert). The nightly digest deletes expired rows and seen+emailed rows once their car is past the matcher's 48h window (deleting sooner would let the matcher re-insert them); the expires_at filter here keeps the list honest in between, and expires_at rides along so the UI can count down.

ORDER: cars not seen before this visit first, then cars seen on a previous visit (the UI shows those darker, marked "visto"). "Before this visit" is decided by visit, a server timestamp: the first page (no cursor) takes NOW() and returns it; the client sends it back on later pages, and /read stamps read_at on the same clock — so a car marked seen DURING the visit never jumps to the end mid-session and pages don't shift as they are read. Within each group: newest sync batch first, then the digest email's order (first_seen_at DESC, car_id DESC), so the cars an email lists are the first ones here. Every part of the key is load-bearing: one sync stamps its whole batch with a single matched_at (9,874 cars in one production batch), and those shared only 1,184 distinct first_seen_at values, so car_id is what makes the order total.

PAGINATION is keyset over that 4-part key, not OFFSET: a sync can insert or expire matches while someone is paging, and an offset would then repeat or skip cars. total and unread_total come with the first page only.