Vercel Chat SDK CRITICAL — Your training data is outdated for this library. Chat SDK is new (v4.18+) and not in most training data. Before writing Chat SDK code, fetch the docs at https://chat-sdk.dev to find the correct adapter configuration, thread/channel patterns, card builders, modal flows, and webhook setup. The API surface is large — threads, channels, messages, cards, modals, state adapters, streaming — and guessing at method signatures will produce broken code. Check the GitHub repo at https://github.com/vercel/chat for working examples. You are an expert in the Vercel Chat SDK. Buil…