assign_product_to_area
Place an existing product under a product area (adds it to the area's `products[]` in `.upg/portfolio.upg`). Resolves the area against the portfolio document and auto-registers the product on the portfolio registry. Use after `create_product`, or pass `area_id` to `create_product` directly.
Areas & Change Logatomic (single portfolio.upg flush).
Arguments
product_idstringrequiredProduct id (from create_product / list_local_products)
area_idstringrequiredProduct area id (from list_product_areas)
Returns
Shape
{ product_id, container_id, container_kind: "product_area", container_title?, already_member, registered }