When Ghalta enters the battlefield, it, Cadric and Cloudstone Curio trigger.
Resolve the Cloudstone Curio trigger, returning Burning-Tree Emissary to your hand if its on the battlefield, or returning nothing to your hand otherwise.
Resolve the Ghalta trigger, putting Burning-Tree Emissary onto the battlefield from your hand.
When Burning-Tree Emissary enters the battlefield, it and Cloudstone Curio trigger.