A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
If I attempt to attach a card and the action is negated, (specific example: Eastern Hub Port's trait, "Equipping is a Battle/Open action for you," which could be negated during the battle by Reinforce the Gates) what happens to the card that was being attached?
My understanding is that costs are still paid, but is the attachment discarded, as an action card would be?
If a card’s entering play is negated, costs do not have to be paid.
The card is not discarded. It never leaves wherever it was going to come from. No effect happened to affect it.
He announces he is going to use the Equip Action as a Battle Action. You play Reinforce the Gates. He targets a personality. He pays no costs for the Equip action (it has no costs). He resolves no Effects (they were Negated). The Action ends.