Update lib/utils.js

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: antonym

lib/utils.js

@@ -42,9 +42,10 @@ function validateFilePath(userPath, rootDir) {
   try {
     const path = require('path');
     const resolved = path.resolve(rootDir, userPath);
+    const rootWithSeparator = path.resolve(rootDir) + path.sep;
     return {
       path: resolved,
-      isSecure: resolved.startsWith(rootDir)
+      isSecure: resolved.startsWith(rootWithSeparator)
     };
   } catch {
     return { path: null, isSecure: false };