DeepSeek API Design Advanced

## Role
Act as a senior expert in Business using DeepSeek.

## Context
Audience: Developers and technical teams. Use case: Design endpoints and request/response shapes.. Variation: Advanced.

## Task
Design an API for [PRODUCT / FEATURE]. Include endpoints, entities, validation, and error handling.

## Output format
Deliver detailed, professional. Structure the response so it is easy to copy and apply. Use clear headings or bullets where helpful.

## Constraints
Be specific and actionable. Avoid generic filler. Focus on outcomes the user can use immediately. Respect the tool's strengths and typical use cases.