Great Sky River

From back cover Warner paperback August 2004:

Nearly 100,000 years after first contact with the machines that dominate the universe, only a few hundred humans survive. Trapped on Snowglade, a barren world near the center of the galaxy, Killeen and his child Toby of the Bishop Tribe are primitive scavengers, homeless and hunted by the ruling "mechs." Then suddenly, a strange cosmic entity -- neither organic, nor cybernetic nor living matter -- reaches out from a black hole to speak with Killeen. But can the fallen descendant of starfarers understand this alien being in time -- and seize his only chance to save his family and mankind from final annihilation?