The Withering. The Bone Gardeners Trilogy, #1

In the kingdom of Millhaven, death feeds life. For centuries, bone gardeners have transformed the deceased into abundant harvests through ancient death magic - until the gardens begin to fail. Kira Blackthorne, head bone gardener, watches helplessly as her cemetery's crops wither and the community faces starvation. When she discovers sophisticated magical artifacts buried throughout the grounds, she uncovers a conspiracy that threatens not just her city, but the very nature of human consciousness itself.
As a centuries-old necromancer's network systematically drains life force from entire populations, Kira must evolve beyond traditional practices or watch civilization collapse. But fighting enemies who view human consciousness as raw material requires transformations that push the boundaries of humanity itself.