Real-Time Support Chat API

I need a seasoned backend developer to architect and code the APIs that will drive an instant-response customer-support chat and text-messaging service. The data layer is fixed on MySQL, so you will design the schema, write migrations, and ensure every query scales cleanly under load.

The chat must feel live—messages should travel round-trip in well under a second—so expect to work with websockets or a similarly performant real-time layer. All traffic, both REST and socket, has to be secured by robust user authentication; agents and customers must only access the conversations they own. File sharing and typing indicators are not in scope right now, but please structure the code so these features can slot in later without rewrites.

Deliverables
• REST and websocket endpoints for chat and outbound SMS
• MySQL schema plus migration scripts
• Token-based authentication middleware integrated across endpoints
• Unit tests, load-test script, and simple health checks
• Postman/Swagger documentation and a README covering local setup, environment variables, and deployment steps

Acceptance criteria
• Messages delivered to all participants in