In towns and cities across the country, a quiet figure is disappearing: the person at the center of a neighborhood's invisible social web — the barber, the pharmacist, the corner store owner — who held informal records of who was struggling, who'd moved away, who needed checking on. This week, we look at what happens to a community's connective tissue when the person who held it together retires, sells up, or simply can't afford to stay — and ask whether anything we're building now can do what they did.