Use when the user wants to attach an image generated or uploaded in the current MCP client conversation to an existing private RecipeBee recipe. Prefer the Apps SDK file input when MCP client supplies file with download_url and file_id. Use image_url only for a URL selected or uploaded in the RecipeBee widget. If neither file nor image_url is available, return a pending selection and do not claim attachment. The widget picker is a fallback because native generated images may not be available in MCP client Files. Report attachment only after persisted=true and needs_image_selection=false. mode=replace changes which retained image is primary but does not delete the previous image; use it only after the user explicitly requests replacement. Do not use for a new RecipeBee-generated image.