url

    invoke:
      tool: "nika:fetch"
      args:
        url: "${{ const.api_base }}/items"   # SLOT: the create endpoint
        method: POST
        headers:
          x-api-key: "${{ secrets.API_KEY }}"  # SLOT: the auth header name
        multipart:
          # Exactly one of `path:` (file) or `value:` (text) per part — a part
          # carrying both, or neither, is refused before anything is sent.