What opens a chain in Riftbound, and can opponents react to units being played?

Ruling: Units and gear (permanents) do create a chain but immediately resolve without lingering on it, essentially closing it right away. Opponents cannot react to the unit itself being played, but can react to triggered abilities (like "When you play me" text) that go on the chain after the unit has entered play.

Sequence:

• When you play a unit, it creates a chain
• The unit immediately falls off the chain and resolves
• If the unit has triggered abilities (like "When you play me"), those abilities go on the chain after the unit has entered play
• Opponents can react to those triggered abilities, not the unit itself

Nuances:

• Spells and abilities linger on the chain and afford reaction opportunities
• Leader abilities like Lee Sin, Ahri, and Leona create triggers that go on the chain
• You react to the ability on the chain, not the unit itself