---

name: PreventionPatterns description: Known bug patterns and their fixes to prevent regression.

<skill_doc>

Prevention Patterns

When reviewing code or debugging, check against these known issues.

🛡️ React/Frontend Patterns

• Missing Dependency: useEffect dependency array incomplete?
• Stale Closures: Using state in callbacks without refs or functional updates?
• Key Props: Using index as key in list rendering? (Bad for re-ordering).
• Zod Schema mismatch: Frontend types not aligned with Backend API responses?

🛡️ Node/Backend Patterns

• Unhandled Promise: Missing .catch() or try/catch in async handlers?
• SQL Injection: String concatenation in queries instead of parameters?
• Env Vars: Hardcoded secrets instead of process.env?
• Race Conditions: Parallel DB updates to the same record?

🛡️ General Code Health

• Slop Variables: data, info, temp, obj. Rename them.
• Deep Nesting: More than 3 levels of indentation? Refactor/Extract.
• Dead Code: Imports unused? Functions never called?

🧪 Post-Mortem Protocol

When a bug is fixed, ask:

1. "Could this have been caught by a type?"
2. "Could this have been caught by a test?"
3. "Could this have been caught by a lint rule?" Add the answer here. </skill_doc>