How does focus work when attacking and playing actions/reactions in a chain, and does focus automatically pass when a chain resolves?

Ruling: When you attack and play an action to start a chain, you are the first who can use a reaction on that chain. Focus automatically passes every time a chain fully resolves. After the attacker plays an action and the chain resolves, the defender has focus and can play an action to start a new chain before the attacker can play a second action.

Sequence:

• Attacker plays an action and starts a chain (attacker can add reactions first)
• Chain resolves completely
• Focus automatically passes to defender
• Defender can now play an action to start a new chain
• That chain resolves, focus passes back to attacker
• Process continues

Nuances:

• Focus automatically passing when a chain resolves is NOT the same as "passing focus" for the purpose of ending a showdown
• A showdown requires both players to actively pass focus (not just chains resolving) in order to end
• The automatic focus pass from chain resolution also does not count as passing at the end of the initial chain