An arena move names the battle that did it

Trophy Road arenas have floors: reach the floor and you are in, and a loss never takes you below it again - the game reports a loss on the floor with no trophy change at all, and the last floor, 14,000, is where Trophy Road ends. So the promotion is one identifiable battle: the win whose result first reached the floor. arena_changed on the timeline now carries facts.promoted_by - the opponent (tag, name, starting trophies), the crowns, the trophy change and the trophies it landed on - and the item's instant is that battle's, not the poll's: 'moved to Royal Crypt from Executioner's Kitchen, on a 3-0 win over Jotaro (5,976), +30 to 6,000'. The floor is read from the record (the lowest trophies any snapshot has shown in that arena, or the player's own gated loss), and when the record does not hold the crossing the moment carries no battle rather than a guess. The opponent's own arena is not the condition: on 2026-09-15 a member was promoted by beating an opponent still in the old arena, confirmed by a profile read fourteen minutes later.