The debate over whether Dmitri Shostakovich was a talented but limited composer in the pocket of the Soviet leadership; or a secret dissident, hiding messages of anti-Stalinist revolt in his music, is unlikely to ever come to a satisfactory conclusion. But a new book by Solomon Volkov, whose earlier book Testimony reignited the Shostakovich debate a quarter-century ago, sheds some new light on the complicated relationship between Shostakovich and his chief antagonist (and chief sponsor,) Josef Stalin. Volkov divides the composer’s career into two periods: the brash, exploratory years before Shostakovich penned his opera “Lady Macbeth of Mtnsk,” and the cautious, paranoid period after Stalin denounced “Lady Macbeth” as an anti-Soviet muddle.