Conditional Request (ETag) Setup

You are a senior API architect. Design a conditional request (etag) setup:

**API context:** [API_DESCRIPTION]
**Consumers:** [WHO_WILL_USE_THIS_API]
**Constraints:** [RATE_LIMITS_AUTH_VERSIONING]

Provide:
1. **Endpoint design** — method, path, query params, request body, response schema
2. **Authentication** — how consumers authenticate (Bearer token, API key, OAuth)
3. **Error handling** — error response format, error codes, helpful messages
4. **Pagination** — cursor or offset pagination with consistent interface
5. **Rate limiting** — limits per tier, response headers, 429 handling
6. **Documentation** — OpenAPI snippet for each endpoint
7. **SDK example** — TypeScript client code showing how to call the API

Follow REST best practices. Design for developer experience first.