For decades, klezmer musicians have kept traditional Jewish music alive despite war, genocide, and erasure. They’ve done so by playing a small handful of surviving songs again and again. Many more songs—a trove of tunes with the potential to redefine the genre—have sat just out of reach, in a former Soviet archive. This music was unseen, unheard, unknown. But now, newly rescued, it’s transforming the klezmer world, the people who work in it, and our picture of 20th-century Jewish life in a destabilized Europe. Rescued: The Lost Treasures of Klezmer tells the story of that music.  Written and produced by…