Stable form id: default c.state key of the answers, the key a native
provider uses to find the published form (e.g. a WhatsApp Flow id mapping),
and the node label in describe(). Same charset as field names.
OptionaltitleTitle shown on the native form screen.
OptionalintroText sent with the form (native message body) or before the first question (degraded).
OptionalctaLabel of the button that opens a native form. Default: core.form.cta in ctx.lang ('Abrir formulario' / 'Open form').
OptionalsubmitLabel of the submit button of a native form. Default: core.form.submit in ctx.lang ('Enviar' / 'Submit').
Fields, in order. At least one; names must be unique.
A transport-agnostic form.