diff --git a/CLAUDE.md b/CLAUDE.md
index 69330dc..c150ea8 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -153,6 +153,11 @@ refactor: move inline YAML to fixtures for better test maintainability
 - Do NOT argue or explain why they might be useful
 - Just comply immediately and recommit without bylines
 
+### 🚫 Commit Messages Over 100 Characters
+
+Commitlint enforces `header-max-length: 100`. Keep commit message first lines under 100 characters.
+The `commit-msg` hook catches this locally if installed via `make pre-commit-install`.
+
 ### ✅ Prevention Mechanisms
 
 **Before writing ANY code:**
diff --git a/Makefile b/Makefile
index c9e3a32..ac33ba3 100644
--- a/Makefile
+++ b/Makefile
@@ -139,6 +139,7 @@ pre-commit-install: ## Install pre-commit hooks
 	@command -v pre-commit >/dev/null 2>&1 || \
 		{ echo "Please install pre-commit or run 'make devtools'"; exit 1; }
 	pre-commit install
+	pre-commit install --hook-type commit-msg
 
 pre-commit-update: ## Update pre-commit hooks to latest versions
 	@echo "Updating pre-commit hooks..."