CIUDAD JUÁREZ, Mexico — At first, the people at the Good Samaritan migrant shelter who have had few reasons to cheer did precisely that. With news that many of them could soon be on their way to the United States, they applauded and embraced in the outdoor plaza, where sagging clotheslines intrude onto the basketball court.

The adults waited for more details, as their children rode exuberantly around the courtyard in the shelter equivalent of Radio Flyers: milk-crate wagons. Hours later, they got more news: Nothing had changed. The stringent Trump administration border policy that has kept thousands of asylum seekers trapped in Mexico would keep them waiting a while longer.

“I feel overwhelmed right now,” said Adela Abigail Castillo de Moreira, an asylum seeker from El Salvador who has been waiting in Ciudad Juárez for a month.

A federal appeals court decision on Friday that could upend the border policy created a chaotic day for thousands of migrants in Mexico’s border cities — at Good Samaritan and other shelters in Ciudad Juárez, at the international bridges and ports of entry in Tijuana and Matamoros.