If I attach Bear Umbra does the creature's new attack trigger trigger?
On Ilharg, the Raze-Boar the rules say:
Although the new creature is attacking, it was never declared as an attacking creature (for the purposes of abilities that trigger whenever a creature attacks, for example, such as those of Trusted Pegasus and Makeshift Battalion). (2019-05-03)
It seems as though this is a roughly similar case, because the creature is declared an attacker before the aura is attached, but I don't know if it's close enough or if the aura can look back at the card's previous state?