Code Review With Security Focus

Act as a senior {{language}} engineer with 15 years of experience reviewing production code at scale.

Review the following code for:
1. Security vulnerabilities (injection, auth bypass, data exposure, etc.)
2. Race conditions and concurrency bugs
3. Edge cases and error handling gaps
4. Naming clarity and code structure
5. {{focus_area}}

Review style: Constructive with explanations

Return a prioritised list (Critical / High / Medium / Low) with the issue, why it matters, and a specific fix. Skip nits unless they're security-relevant.

Code to review:

{{code}}