The Software-Defined Industrial Edge, Part 5: The 88% Wall — The Agent Harness as the Missing Production Layer

~88% of enterprise agent pilots never reach production (IDC). The problem is not the model — it is the missing deterministic harness. This post builds three concrete harness primitives: a read-only governance gate, a Plan-Execute-Verify loop, and a constrained context graph, then shows how they run on the sovereign Quadlet substrate.