Which stay a day wakes up in and which one it sleeps in was decided in the
client's Days view only. The rule, with the day order, the stay range and the
check whether the hotel is the edge stop itself, now lives in shared under
day/stay-bookends, typed on the few fields it reads, so the road trip in the
browser and on the server can make the same choice as Days. The Days helpers
re-export it unchanged, and their tests pass untouched; nothing behaves
differently.
Maurice