You are building a customer support assistant on Databricks. The application must handle two very different request types: (1) factual questions that should be answered from a Vector Search-backed knowledge base, and (2) requests to calculate refund amounts that require a deterministic Python function. Both request types arrive at the same chat endpoint. You want a single LangChain LCEL pipeline that inspects each incoming query and dispatches it to the appropriate sub-chain. Which LCEL construct is the most appropriate way to implement this dispatch logic?