A salsiccia fold is a hot filling in a hot bread, and that shared heat is the point. Fresh pork sausage, split and cooked on a flat top or grill until the skin browns and the inside stays juicy, goes into a Romagnolo round straight off the same kind of heat. Nothing here needs to be loosened by warmth, because nothing is cold; instead the appeal is a single sustained register of hot, fatty, savoury, with the soft blistered flatbread absorbing the rendered fat and keeping the sausage from drying as it sits. The defining fact is that the piadina is doing structural work, holding a loose, greasy, crumbling filling together in the hand in a way a flat plate never could.
Making it well is about cooking the sausage right and matching textures. The dough is flour, lard or oil, water, almost no leavening, rolled thin and griddled dry until it freckles and stays foldable, pulled before it stiffens so it bends around a bulky filling without cracking. The salsiccia is usually split lengthwise and laid flat so it browns on a wide face and packs evenly into the fold rather than rolling out of it, the casing crisped a little for contrast against the soft crumb. A smear of soft fresh cheese is common, melting against the warm sausage and binding the fold, as is a few wilted greens for a bitter edge. It is folded in half and eaten hot, while the fat is still loose and the bread is still soft.
The near relatives are one swap from here and stay regional. There is the version finished with sweet sauteed onion for a caramelised counterpoint, the one with bitter greens cooked down beside the sausage, and the fold that uses a coarser, spicier southern sausage for more heat. Each is the same warm round meeting a single changed element, and each deserves its own article rather than being crowded in here.