For a brief, enticing stretch of Guillaume Canet ’s Karma , it appears to be a film in which Canet’s ex-wife Marion Cotillard plays an alcoholic employed at a Spanish sardine factory. We haven’t seen Cotillard do exactly that before, so that would be a novelty, and it might be nice to watch her in another working-class social drama, all these years after her Oscar-nominated turn in Two Days, One Night . But something about Karma ’s sinister music tells us that Canet, who also co-wrote the film, has grimmer matters in mind. We only see the sardine factory once before the film’s true plot kicks in. What Karma is really about is a subject familiar to many an American consumer of streaming-service documentary series. No, it’s not about a scam artist or a mysterious campus murder. It is, instead, about a cult, a cloistered religious community run by an abusive false prophet.…