A semantic skill selector can make an agent prompt smaller. It can also make an agent less capable if it quietly removes the only map to available skills. That is the boundary APX needs to protect. APC is the portable context layer. A project can keep reusable instructions in .apc/skills/ , review them in Git, and share them with compatible tools. APX is the local runtime layer. It decides what becomes active during one turn: a small catalog hint, a loaded skill body, or an optional seman...