Regex Catastrophic Backtracking: The Tiny Pattern That DOS's Your Service

An innocent-looking regex like `^(a+)+$` can hang your entire service when fed the right input. It's not a bug in your code -- it's the regex engine doing exponential backtracking on a pattern that looked fine in tests. Once you know the pattern, you'll find ReDoS vulnerabilities in places you didn't expect, including npm packages you depend on.