Instrument Vercel AI experimental_evaluate #24692

[email protected] added experimental_evaluate. In [email protected], it also publishes on the ai:telemetry tracing channel with type: 'experimental_evaluate' (vercel/ai#21162). Our v7 channel subscriber ignores unknown event types, so these calls make no span today.

Scope

• Change only the v7 channel subscriber (packages/server-utils/src/integrations/vercel-ai/vercel-ai-dc-subscriber.ts). The function does not exist in ai v4 to v6.
• Make one span for each call. The channel does not publish the inner model call.

Target span

• Name: evaluate <modelId>, op gen_ai.evaluate, origin auto.vercelai.channel
• gen_ai.operation.name: evaluate, gen_ai.provider.name (raw provider ID, for example typesafe.evaluation), gen_ai.request.model, gen_ai.response.model
• gen_ai.usage.input_tokens, output_tokens, total_tokens
• gen_ai.input.messages: [{ type: 'evaluation', state, questions }] (only when recordInputs is on)
• gen_ai.output.messages: [{ type: 'evaluation', answers }] (only when recordOutputs is on)
• Keep the shared vercel.ai.* attributes that other Vercel channel spans have.

Notes

• @sentry/conventions has no gen_ai.evaluate op yet.
• Add a node-integration test. It needs ai >= 7.0.111 in the test app.