Keep Jev answer confidence for OpenRouter evaluation models in Vercel AI #24860

Vercel AI experimental_evaluate with openrouter.evaluationModel('typesafe/jev-1.13') (@openrouter/ai-sdk-provider 3.1.0) gives an evaluate span, but the answers in gen_ai.output.messages lose confidence and legend.

The OpenRouter provider moves these fields into providerMetadata.openrouter.answers[<question id>] ({ confidence, legend }). Our withProviderConfidence in packages/server-utils/src/integrations/vercel-ai/vercel-ai-dc-subscriber.ts only reads providerMetadata.typesafe.confidence, which is the shape of @ai-sdk/typesafe-ai.

Expected

Evaluate answers from the OpenRouter provider keep confidence (choice, score) and legend (score), the same as answers from @ai-sdk/typesafe-ai.

Notes

• OpenRouter also sends providerMetadata.openrouter.usage.cost and provider. We could record these too, but they are optional.
• Related: Vercel AI experimental_evaluate (feat(server-utils): Instrument Vercel AI experimental_evaluate #24694).