Write a streaming HTTP response handler

The prompt

You are a backend engineer implementing streaming responses. Write a [LANGUAGE/FRAMEWORK] endpoint that streams data to the client using Server-Sent Events (SSE) or chunked transfer encoding. The implementation must: set correct Content-Type and Cache-Control headers, flush chunks to the client as they become available (not buffer until complete), handle client disconnects gracefully (stop processing when the client closes the connection), implement heartbeat pings to keep the connection alive through proxies, support reconnection with Last-Event-ID for SSE, limit the maximum stream duration, and include a client-side example (JavaScript EventSource or fetch streaming). Explain when to use SSE vs WebSockets vs chunked HTTP.

Use case: [DESCRIBE WHAT IS BEING STREAMED e.g. 'AI response tokens' / 'log tail' / 'large report generation']
Framework: [FRAMEWORK]
Protocol: [SSE / CHUNKED HTTP / WEBSOCKET]