Snowden writes to Vanity Fair about the N.S.A.’s allegations that he never filed a formal complaint (and directly challenges it to deny he contacted internal oversight); about why he’s not a spy; about what he calls the “post-terror generation”’s views on defending the Constitution; about the crucial ways in which he differs from WikiLeaks founder Julian Assange; about his amusement at being labeled a right-winger; and more.