tidyr's nest() and unnest() seem to order-preserving (i.e. stable) in my testing, where the elements of each nested list are in the same relative order as their original row ordering in the unnested data frame (and vice-versa for unnest()). But I haven't found any documentation stating this is the intended/guaranteed behavior.
Does anyone know if stable nesting/unnesting is by design and to be expected for future versions of tidyr?