BOSTON — Prosecutors and lawyers for Boston Marathon bomber Dzhokhar Tsarnaev are sparring over whether an agreement that allowed a loosening of communications restrictions on Tsarnaev in prison should continue now that he has been convicted and sentenced to death. After Tsarnaev was charged in the deadly 2013 bombing, his communications with the outside world were sharply limited, materials shown to him by his lawyers were inspected by prison officials and his visits with his lawyers were monitored. In 2014, Tsarnaev’s lawyers complained that the measures were so restrictive they impeded their ability to prepare his defense. The “special administrative measures” put in place for Tsarnaev have also been used in other terror cases and are designed to prevent suspects from communicating with others to incite violence. Under an agreement between both sides, some restrictions were loosened.