I'll regularly get messages like "such and such an 'upgrade' added to the 'shop.'" There are half a dozen of these shops, each with a different set of upgrades, but none of them are called "shop" or "upgrades," which I think means I haven't found the upgrade shop yet? Except that if I look at the list of achievements, I have purchased ~90 upgrades. Obviously the move is to revisit the achievement interface after every action to see if the thing I just did is buying an upgrade from the shop.