Streaming Responses in Next.js App Router — Server-Sent Events and ReadableStream

Long-running operations create a UX problem. A request that takes 10-30 seconds leaves users staring at a spinner with no indication of whether anything is happening. Streaming lets you send partial results as they become available — the user sees progress rather than nothing. Next.js App Router has solid streaming support through two approaches: React Suspense for component-level streaming, and ReadableStream/Server-Sent Events for API-level streaming. Here's how both work in production, includ