Forward-trims are the single most frequent thing a Booking.com feed does. Because the trim happens on almost every export, Lemon sees it on almost every five-minute fetch of every in-progress stay: 1,240 elapsed_checkin_pinned decisions between 2026-09-05 and 2026-09-10.
Before Lemon's identity rules, a forward-trim was interpreted as a date change (job reset, cleaner messaged) or, where an identifier included the check-in date, as a disappearance (job cancelled, then recreated five minutes later). Rule 3 — an already-elapsed check-in is immutable for every feed — and rule 4 — only the checkout drives the clean — remove both effects.