Next.js e2e: Vercel AI tests are disabled since v11 #25781

Description

No e2e test covers AI SDK tracing in a Next.js app. #22501 marked the AI tests in nextjs-15 and nextjs-16 as test.fixme, because those apps pin ai@^3 and #22701 dropped v3 support. nextjs-16-static (#23834) copied the disabled tests:

• nextjs-16/tests/ai-test.test.ts and ai-error.test.ts, the same two in nextjs-15 and nextjs-16-static
• nextjs-16-streaming and nextjs-16-tunnel also pin ai@^3, with no AI tests

The Node integration tests cover ai v4–v7. Nothing covers the Next.js-specific path: ai bundled into a route handler by Turbopack or webpack, then instrumented at runtime.

Next step: upgrade these apps to ai@^7 (MockLanguageModelV3), call generateText and streamText from a route handler, and re-enable the tests. Related: #24751.