A financial services company is building a customer-support assistant using Amazon Bedrock Knowledge Bases. The source data consists of conversational chat transcripts where a single customer issue often spans many short back-and-forth messages, and the meaning of any one message depends heavily on surrounding context. Early testing with the default fixed-size chunking (300 tokens) shows the retriever frequently returns fragments that split a single question-and-answer exchange, causing incomplete and confusing responses. The team wants Bedrock to group text into chunks based on topical/meaning boundaries rather than arbitrary token counts, without writing a custom ingestion pipeline. Which chunking configuration should they select when creating the data source?