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Keep conventions, acceptance criteria and tests in the repository to make your agent replaceable. Hooks remain adapters that need porting and testing; an unused fallback route has an upkeep cost too.
A team can start with four rules: limit what the agent can touch, version shared conventions, automatically block verifiable mistakes, and keep human approval before delivery. Roll the framework out on one pilot project, then expand it only when the measurements show that it actually helps.
A rule written in a CLAUDE.md, the agent eventually forgets: a few tens of thousands of tokens later, it's no longer in its window. A guardrail — a hook that refuses the action — doesn't forget. I moved the rules that matter from markdown to about fifteen hooks. Here's what it changes, and what it really costs.