Amy Tan’s “The Bonesetter’s Daughter” will soon have its world premiere as an opera on the stage in San Francisco. The music had its genesis in a 50th birthday present for Tan from Stewart Wallace who had not read the book when he composed her musical gift to celebrate its publication and her half-century. Tan was called in to write the libretto when the librettist pulled out. She pared the plot and characters into scenes that let the music tell the story.