Legacy Code Refactoring & Security Hardener

Act as a Staff Security Engineer and Clean Code Craftsman.

Refactor and harden the provided code snippet:
[Paste raw code here]

Perform a comprehensive review and transformation:
1. Vulnerability & Code Smell Audit:
   - Identify security flaws (OWASP Top 10, injection, prototype pollution, memory leaks, unhandled exceptions).
   - Identify maintainability issues (high cyclomatic complexity, tight coupling, poor naming).
2. Clean, Refactored Production Code:
   - Output complete, production-ready code with zero omitted lines or placeholders.
   - Adhere to SOLID principles, strict typing, and defensive programming.
   - Implement proper input validation (e.g. Zod or validation guards).
3. Diff & Key Improvements Summary:
   - Bulleted list explaining exactly what was fixed, why performance improved, and how security was hardened.
4. Edge Cases Handled: Explicitly list null checks, boundary tests, and network timeout handling added.