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.
A player, 18 March 2013
Relevant Cards
Card Title The Golden Plains PS/GP/SH 7 3 7 Text Recon Reaction: After engaging: You have Reconnaissance at the current battlefield. Create a Terrain Strategy with the ability, "Battle: If this card is in play, destroy it and target a Terrain in your hand: Take an additional Battle action to play it." Put it into play there.
and
Card Title Jade's Roar Force/Chi 4 2 HR/GC/PH - 7 0 Keywords Experienced Pride of the Hand • Legendary • Lion • Lion Clan • Nonhuman • Scout • Unique Text Recon Reaction: After engaging at Jade's Roar's battlefield: You have Reconnaissance there. You have the first opportunity to take a Battle action in this battle, which must be a Terrain action.
Say I am attacking and I announce Jade's Roar reaction upon engaging and my opponent then announce The Golden Plain's reaction after that when it comes time to the action rounds since there is now a terrain in play and I cannot play one what happens? Do I have to pass?
Jon Palmer (rules official), 18 March 2013
Relevant Cards
Card Title The Golden Plains PS/GP/SH 7 3 7 Text Recon Reaction: After engaging: You have Reconnaissance at the current battlefield. Create a Terrain Strategy with the ability, "Battle: If this card is in play, destroy it and target a Terrain in your hand: Take an additional Battle action to play it." Put it into play there.
and
Card Title Jade's Roar Force/Chi 4 2 HR/GC/PH - 7 0 Keywords Experienced Pride of the Hand • Legendary • Lion • Lion Clan • Nonhuman • Scout • Unique Text Recon Reaction: After engaging at Jade's Roar's battlefield: You have Reconnaissance there. You have the first opportunity to take a Battle action in this battle, which must be a Terrain action.
Say I am attacking and I announce Jade's Roar reaction upon engaging and my opponent then announce The Golden Plain's reaction after that when it comes time to the action rounds since there is now a terrain in play and I cannot play one what happens? Do I have to pass?
Unless another effect would allow you to play a Terrain in that situation, then yes, you are forced to pass.