Function from_untrusted_json_value 

pub fn from_untrusted_json_value(
    graph: &SchemaGraph,
    ty: &SchemaType,
    json: &Value,
) -> Result<SchemaValue, RenderError>

Decode externally supplied JSON without allowing it to construct host-managed capabilities. Rejection happens when the selected value path reaches a capability leaf, so absent options and unselected sum-type arms remain valid.