what exactly is the prerequisite for prompting the mayor to let you summon the merchant? my first time through he let me summon it at prosperity 3, but i've started over a few times to improve my efficiency, and each time the mayor makes me wait longer before letting me get the merchant. this time i'm at prosperity 12 and he still isn't letting me summon it. is it a bug? what am i doing wrong here? other than that, fun little idle-type game here.