Instrumenting Next.js SSR process

### Problem Statement

Looking at the Next.js trace it produces out of the box, there's a period after "data fetching" and starting to send back the response that's not instrumented and looks blank.


I'm assuming this is when Next.js renders the React component subtree, and generates HTML + RSC Payload, but it's not really self-explanatory. Is it possible to add spans to make it clear to the users what happens during that period?

### Solution Brainstorm

Spans!