When do 'When I move/attack/defend' triggers resolve, and what happens if a unit like Yasuo is killed after triggering 'When I attack' but before combat damage?

Ruling: 'When I move' triggers resolve on their own chain before the showdown begins. Once that chain resolves, the showdown starts and 'When I attack' and 'When I defend' triggers go on a new chain together. Yasuo's 'When I attack' ability triggers and resolves as soon as he becomes an attacker, dealing damage before he can be killed by non-reaction speed cards like Hextech Ray, but he will die before dealing combat damage.

Sequence:

• Unit moves to battlefield, 'When I move' trigger goes on chain
• Move trigger chain resolves (reactions can be added)
• Showdown begins: 'When I attack' triggers are added to new chain
• 'When I defend' triggers are added to same chain
• Reactions can be added
• Chain resolves in reverse order
• Players pass focus back and forth, starting new chains with actions/reactions
• Once both players pass in a row, combat damage is dealt

Nuances:

• Non-reaction speed cards cannot be played until the chain is empty, so they cannot interrupt triggered abilities
• If a unit is moved into an already ongoing combat (e.g., with Ride the Wind), the move trigger goes on the same chain as the attack/defend trigger, with move resolving before attack/defend
• 'When I attack' and 'When I defend' triggers only happen once per combat, even if the unit leaves and returns to the same combat
• Units moved into combat after it starts still trigger their 'When I attack' or 'When I defend' abilities when they gain attacker/defender status