The phrase "didst sly" is an old-fashioned way of saying "you slyly did." Synonyms for this phrase include "you cunningly accomplished," "you deviously achieved," "you sneakily performed," and "you artfully executed." These phrases all imply that someone did something in a clever or sneaky way, perhaps without anyone else noticing. Other synonyms might include "you shrewdly accomplished," "you slyly procured," or "you skillfully executed." The context of the phrase will determine which synonym is most appropriate. Regardless, all of these phrases describe someone who accomplished something in an underhanded or clever way.