The curation is the product. That has been true since 2006, when Pitchfork started programming a festival the same way it programs a review — with a position about which artists matter. Three days at Union Park in Chicago each July: career-defining retrospective sets, reunions, debuts from artists who would otherwise play clubs. Union Park is a city park, not a field miles from anything, which means the festival experience is woven directly into Chicago. Three stages are positioned close together and easy to navigate — you can catch the end of one set and make it to another stage for the opening notes without running. The crowd is music-literate …