add

.claude/hooks/check-gstack.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+# Block skill usage when gstack is not installed globally.
+if [ ! -d "$HOME/.claude/skills/gstack/bin" ]; then
+  cat >&2 <<'MSG'
+BLOCKED: gstack is not installed globally.
+gstack is required for AI-assisted work in this repo.
+
+Install it:
+git clone --depth 1 https://github.com/garrytan/gstack.git ~/.claude/skills/gstack
+cd ~/.claude/skills/gstack && ./setup --team
+
+Then restart your AI coding tool.
+MSG
+  echo '{"permissionDecision":"deny","message":"gstack is required but not installed. See stderr for install instructions."}'
+  exit 0
+fi
+
+echo '{}'