Hold one turn of a conversation with the full shopping agent. The agent interprets the shopper's message, decides what it needs, and answers from whichever sources the domain has configured: product discovery across search, browse and recommendations, and a knowledge base of articles for questions the catalog cannot answer. A single turn can produce several kinds of content, so a reply may combine prose with product sets, cited articles, images or recipes, and it usually ends with refinements the shopper can pick from to continue. parameters.domain chooses which configured domain answers, and with it the agent's instructions, tools and models. Pass thread_id from a previous turn to continue that conversation with its history intact; omit it to start a new one. Results stream back as server-sent events (text/event-stream) so the agent's reply can be rendered as it is produced. To receive the finished reply as a single JSON document instead, send Accept: application/json.