Function from_json 

pub fn from_json(value: Value, target: &Type) -> Result<ArgValue, Error>

Binds a JSON argument value to its ArgValue.

One path for every argument: a tagged value decodes from its tags via [decode_tagged] regardless of kind, while a bare value (no tag) is coerced via the param’s flat TIR Type — the legacy form a top-level scalar may still take.