When are abilities like shield checked in combat - are they checked once at the start of showdown or rechecked throughout combat when the battlefield state changes?

Ruling: Assault and Shield statuses are applied immediately after combat starts, before when I attack/defend triggers. They cannot be reacted to and remain active throughout the entire combat, even for units that enter combat afterwards.

Sequence:

• Combat begins
• Assault and Shield statuses are applied immediately
• When I attack/defend triggers occur
• Statuses remain active for the rest of combat

Nuances:

• If a unit like Wielder of Water gains might from attacking alone, it will recheck after every cleanup step (such as after Ride the Wind resolves) and lose the might gain if it's no longer alone
• Units that enter combat after it has started still benefit from Shield/Assault statuses that were applied at the start