Hal Prince and Steven Sondheim are collaborating on a new show for the first time in 22 years. “Prince has directed more than 30 shows in New York alone, and to sit down with him is to confront a half-century of American theater history. His name instantly evokes an almost unparalleled parade of over-the-moon triumphs, noble failures and, yes, a few bewilderments. When he attaches himself to a project, theatergoers take notice. The last is even more true of Sondheim, of course. Devotees will be making long flights to Washington in the fall to check up on this latest venture. “