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.
Sequence:
Attacker Announces reserve equip of Dark Naga Ambusher. Attacker interrupts with Dark Naga Ambusher to take additional action. Defender interrupts with the Sun Returns to negate the equip action.
Question: will the Dark Naga Ambushers be discarded during step F?
Sequence:
Attacker Announces reserve equip of Dark Naga Ambusher. Attacker interrupts with Dark Naga Ambusher to take additional action. Defender interrupts with the Sun Returns to negate the equip action.
Question: will the Dark Naga Ambushers be discarded during step F?
It stays in your hand.
When Equipping an attachment using the rulebook ability, or other ability not on the attachment itself, the attachment stays in your hand if it does not enter play.
(Conversely, if the Equip effect comes from an ability on the card itself, such as Hidden Reserves, the card is played like a strategy: it enters a Resolution Area when the action is announced, and is discarded after the Resolution of the action if it fails to enter play.)