'Rosencrantz and Guildenstern are Dead' seems to plat around in the same basic sandbox as your play does - the characters never quite get to the point of figuring out that they're in a PLAY, but they do figure out pretty quickly that they have an absolutely minimal part in the story of 'Hamlet', and spend most of their time arguing about why they're there in the first place. Had you read/seen 'R&GaD' before you wrote your play?