🔐 This endpoint requires HTTP Bearer authentication.

Send one blocking A2A 1.0 SendMessage turn to a configured AI Shopping Agent domain. This endpoint uses the same per-domain A2A opt-in as the public agent card and requires a Constructor bearer token authorized for the company that owns the requested index key. Reuse the same contextId for later turns in the same conversation. The response is a terminal A2A task containing text/plain parts and, when accepted by the caller, application/json structured event parts. Streaming, push notifications, deferred execution, and task-management methods are not supported.