NEW YORK — Not long before Election Day, 2016, Samira Ahmed completed the first draft of her novel, “Internment,” a dystopian narrative about the rounding up of Muslim-Americans. As the news came in that Donald Trump had been elected, Ahmed received a text from a friend who had read the manuscript and feared Ahmed had written a work of prophecy. “She said, ‘I hope you’re not Cassandra,'” Ahmed told The Associated Press during a recent telephone interview. Novels about immigrants, like immigration itself, are a long and central part of American culture.