Is Ravenbloom Conservatory a trigger that can be reacted to, and when do you reveal cards for it?

Ruling: Ravenbloom Conservatory is a trigger that goes on the initial chain when a combat showdown starts and a player controlling it is assigned defender. Both players can react to this trigger before it resolves.

Sequence:

• When combat showdown starts and the Conservatory's controller is assigned defender, the trigger goes on the initial chain
• Defender's triggers are last on the chain, so defender has priority
• Both players have an opportunity to react before the trigger resolves
• When the trigger resolves, you reveal the cards (this may be the first thing that happens when resolving that initial chain)