Vercel AI SDK — Align with gen_ai RFC #153

[andreiborza]

Align the Vercel AI SDK integration with RFC #153.

Attribute renames

• gen_ai.system → gen_ai.provider.name
• gen_ai.request.available_tools → gen_ai.tool.definitions (structured objects, not JSON string)
• gen_ai.response.text → gen_ai.output.messages
• gen_ai.response.tool_calls → gen_ai.output.messages
• gen_ai.usage.cache_creation_input_tokens → gen_ai.usage.input_tokens.cache_write
• gen_ai.usage.cache_read_input_tokens → gen_ai.usage.input_tokens.cached

Required attributes

• gen_ai.operation.name set on all spans
• gen_ai.provider.name set on all AI Client spans
• gen_ai.response.streaming set on all AI Client spans
• gen_ai.response.time_to_first_token for streaming responses

Message format

• content → parts in gen_ai.input.messages and gen_ai.output.messages
• System messages extracted to gen_ai.system_instructions

Vercel AI-specific

• Move hardcoded gen_ai.* string literals to shared constants (e.g. gen_ai.function_id, gen_ai.usage.output_tokens.reasoning, gen_ai.usage.input_tokens.cache_miss)
• Update ai.* → gen_ai.* mapping in processEndedVercelAiSpan()
• Update Cloudflare variant (packages/cloudflare/src/integrations/tracing/vercelai.ts)

[linear-code]

JS-2326