AI Gateway logs now show session affinity

Vercel AI Gateway now includes session affinity in its logs, grouping related requests into sessions based on a shared session ID or a fingerprint of the initial conversation. This enables tracking of session duration, cache hit rates, model usage, provider routing, and input caching efficiency across multiple turns, with filtering available by various criteria including model, provider, cost, and authentication. Sessions are automatically maintained across requests using the same provider unless explicitly changed.