This article was originally published on EthereaLogic.ai . The first article in this series introduced the five-layer governance stack and made a single load-bearing claim: the layers that live in documents are necessary, and the layers that run as code are what make the system trustworthy. This article goes inside the highest-leverage code layer — runtime enforcement via Claude Hooks — and shows what one looks like at the level of detail an engineering team would actually need to build it. The thesis of the first article was that an instruction in CLAUDE.md or AGENTS.md can be ignored, reasoned around, or context-windowed out of an agent's working memory, but a hook that exits with status 2 cannot. The thesis of this article is that turning the abstract idea of a hook into a guard that holds under real subagent traffic is its own engineering discipline — one with a small but distinct set of patterns, failure modes, and tests. Most teams who reach the hook layer underestimate that engineering discipline.…