## Context
Native OTel reporting loses input/output values in Langfuse. With a console span exporter the attributes `input.value`/`output.value` are visibly set, but Langfuse shows empty input/output on the trace.
## Verified resolution
Two concrete findings came out of the thread (maintainers hassiebp and Steffen911): (1) in Next.js 14 the span processor may never flush inside serverless functions, Next 15's `after()` (not Next 14's `waitUntil`) is the recommended place to schedule the Langfuse flush, and `exportMode: 'immediate'` on LangfuseSpanProcessor forces immediate export; (2) `langfuse-vercel` is deprecated, maintainer hassiebp confirmed it and the docs were updated to point at the @langfuse/otel-based integration.