Many workplaces, and most union contracts, give senior staff first call on hours. A schedule built only to minimise payroll hands the cheap shifts to the newest, lowest-paid people, which is exactly what a seniority grievance is about.
Shift Roster Builder now reads a seniority: 3 cell (higher means more senior). After the roster is built, it checks each shift held by a junior person. If a more senior person is available and has the role, and giving them the shift keeps every hard rule (rest between shifts, weekly hours, days in a row, overlap), the page lists it with the payroll change and whether the senior is under their minimum hours.
It is a report, not a search rule, so the roster itself does not change. Contract terms such as bidding rounds or hours guarantees are not modelled, and the page says so. A manager can use the list to decide which swaps to make, and what each costs.