What is the correct phase order during a Showdown in Riftbound, and when can players play spells versus reactions?

Ruling: During a Showdown, "When Attacking" and "When Defending" abilities trigger before players get a chance to play spells. Players can only play reactions while triggered abilities are on the chain, but once that chain resolves (or if no triggered abilities exist), the attacking player gets priority to start a new chain with a spell, then the defender gets a chance if the attacker passes.

Sequence:

• Showdown starts
• Assailants get buffed
• Shielders get buffed
• "When Attacking" effects activate and trigger a chain
• "When Defending" effects activate and are put on the chain
• If a chain exists, players can only play reactions until it resolves
• After the chain resolves (or if no triggered abilities existed), the attacking player has priority to play a spell
• If the attacker doesn't play anything, the defender gets a chance
• This loops until both players pass without opening a chain
• Damage calculation occurs
• The respective player scores

Nuances:

• If you move a unit with "when I move" ability to start the showdown, that move trigger goes on the chain before "When Attack/Defend" triggers
• If multiple "when I move" effects trigger simultaneously, the owning player selects the order to place them on the chain
• If moving to an open battlefield, you skip the middle combat steps