Maple agent tracing: Vercel AI SDK

Goal

One conversation = one Maple Agent Session, one turn per generate()/stream() call, with the transcript, every model call (model, tokens, TTFT), every tool call (name, args, result, failures), and a lane per sub-agent.

Known gaps (tell the user, don't try to fix): cost shows as "unpriced" (AI SDK emits no cost; Maple never prices tokens); on AI SDK 5/6 the final assistant reply is missing from transcripts. If model calls go through OpenRouter, its Broadcast traces carry per-call cost and Maple matches them to the AI SDK chat spans by response id (see the OpenRouter guide).

Step 0: Detect