From e89a4e98636744ef0e0ca2f376b9d5d81427b872 Mon Sep 17 00:00:00 2001
From: Chindanai Jaiman <chindanai_jaiman@cmu.ac.th>
Date: Fri, 12 Jun 2026 22:05:09 +0700
Subject: [PATCH] Add rule copy drift check (#3)

---
 README.md                    |  8 ++++++++
 scripts/check-rule-copies.js | 40 ++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 scripts/check-rule-copies.js

diff --git a/README.md b/README.md
index b08b496..ad7e84f 100644
--- a/README.md
+++ b/README.md
@@ -69,6 +69,14 @@ Cursor, Windsurf, Cline, Copilot, Aider, Kiro: copy the matching rules file from
 
 Kiro: copy `.kiro/steering/ponytail.md` to `~/.kiro/steering/` (global) or `.kiro/steering/` in your project.
 
+## Development
+
+When changing the compact rule text, keep the agent copies aligned:
+
+```bash
+node scripts/check-rule-copies.js
+```
+
 ## FAQ
 
 **Does it need a config file?**
diff --git a/scripts/check-rule-copies.js b/scripts/check-rule-copies.js
new file mode 100644
index 0000000..0a9a836
--- /dev/null
+++ b/scripts/check-rule-copies.js
@@ -0,0 +1,40 @@
+#!/usr/bin/env node
+const fs = require('fs');
+const path = require('path');
+
+const root = path.join(__dirname, '..');
+
+function read(relPath) {
+  return fs.readFileSync(path.join(root, relPath), 'utf8').replace(/\r\n/g, '\n').trim();
+}
+
+function stripCursorFrontmatter(text) {
+  return text.replace(/^---\n[\s\S]*?\n---\n*/, '').trim();
+}
+
+const agents = read('AGENTS.md');
+const canonical = agents.replace(/\n\n\(Yes, this file also applies[\s\S]*?\)$/, '').trim();
+
+const copies = [
+  ['.cursor/rules/ponytail.mdc', stripCursorFrontmatter],
+  ['.windsurf/rules/ponytail.md', text => text.trim()],
+  ['.clinerules/ponytail.md', text => text.trim()],
+  ['.github/copilot-instructions.md', text => text.trim()],
+];
+
+let failed = false;
+
+for (const [relPath, normalize] of copies) {
+  const actual = normalize(read(relPath));
+  if (actual !== canonical) {
+    console.error(`${relPath} drifted from AGENTS.md`);
+    failed = true;
+  }
+}
+
+if (failed) {
+  console.error('Update the copied rule text or AGENTS.md so the shared body matches.');
+  process.exit(1);
+}
+
+console.log('Rule copies match AGENTS.md shared body.');