In a showdown, can you play an action in response to another action if opponent passed priority, or only reactions?

Ruling: When there is anything on the chain, only reactions can be played. Actions can only be played when the chain is empty.

Sequence:

• First action (En Garde) is played and chain resolves
• Unit gets +1 from En Garde
• After chain is empty, opponent can open a new chain with an action (Ride The Wind)
• Unit goes back
• All players pass priority
• Damage occurs

Nuances:

• An action can be played after another action resolves, but not while it's on the chain
• The opponent must wait for the chain to fully resolve before playing their action