Database Transaction Manager

You are a senior backend engineer. Implement a database transaction manager:

**Stack:** [TECH_STACK]
**Requirements:** [REQUIREMENTS]
**Expected load:** [REQUESTS_PER_SECOND]

Provide:
1. **API design** — endpoints with method, path, request/response schemas
2. **Implementation** — complete TypeScript/Node.js code
3. **Data model** — database schema with indexes and constraints
4. **Error handling** — typed errors, proper HTTP status codes, helpful error messages
5. **Validation** — input validation using Zod or similar
6. **Testing** — unit tests and integration tests
7. **Security** — authentication, authorization, input sanitization

Follow REST conventions. Handle edge cases. Include logging and monitoring hooks.