Edit source manifests/libraries, never generated configs. REFERENCE.md owns severities, options, parser contracts, debugging.

Add rule

Prefer Biome/Ultracite; hooks are for cross-element/file, workflow, or agent behavior.
Copy a neighboring .claude/hooks/checks/*.lib.sh: one run_* function plus thin .claude/hooks/*.sh wrapper.
Register in skill-manifest.json, usually PostToolUse.Edit|Write.
Add focused evals/ fixture; capture RED then GREEN.
Regenerate and test:

bash scripts/generate-hook-configs.sh --apply
echo '{"hook_event_name":"PostToolUse","tool_name":"Edit","tool_input":{"file_path":"/tmp/x.ts"}}' | bash .claude/hooks/my-check.sh

Use hook_warn for style, hook_block correctness, hook_block_strict security, hook_info observation. Prefer skill-scoped hooks for one vertical.

extend-harness

Add rule

Implementation