Claude Code Review: SQL payment gateway

I need you to act as a senior software engineer conducting a thorough code review for a SQL project building a payment gateway.

**Why Claude excels here:** This requires careful line-by-line analysis, understanding architectural patterns, identifying subtle bugs, and providing constructive, educational feedback.

**Tech context:** Next.js + TypeScript
**My role:** mobile developer

## Code Review Instructions

### Phase 1: Architecture Review
- Evaluate the overall project structure and organization
- Assess separation of concerns and modularity
- Check for adherence to SQL best practices and idioms
- Identify any architectural patterns being used (or misused)
- Flag any scalability or maintainability concerns

### Phase 2: Code Quality Analysis
For each file or module reviewed, assess:
- **Correctness:** Are there logic errors, off-by-one errors, race conditions, or edge cases?
- **Security:** SQL injection, XSS, authentication flaws, insecure defaults, exposed secrets?
- **Performance:** N+1 queries, unnecessary re-renders, memory leaks, blocking operations?
- **Readability:** Naming conventions, function length, comment quality, code organization?
- **Error handling:** Are errors caught, logged, and handled gracefully?
- **Type safety:** Proper typing, avoiding any/unknown, null safety?

### Phase 3: Specific Improvements
For each issue found, provide:
1. The problem: what is wrong and why it matters
2. The severity: critical / major / minor / suggestion
3. The fix: show the corrected code with explanation
4. The principle: what general rule this demonstrates

### Phase 4: Positive Feedback
- Highlight 3-5 things done well in the codebase
- Note any clever solutions or good patterns

### Phase 5: Summary
- Overall code health rating (1-10 with justification)
- Top 5 priority items to fix first
- Recommended next steps for improving code quality
- Suggested tools or linting rules to prevent future issues

Be specific and constructive. Every criticism should come with a solution. Explain the "why" behind each recommendation so the developer learns, not just fixes.

Please paste the code to review, or describe the specific modules and I will walk through them with you.