Function run_json_handler 

pub fn run_json_handler<Req, Resp>(
    handler: &mut dyn Handler<Req, Resp>,
    json_body: &str,
    world: &mut World,
) -> Result<String, String>
where
    Req: DeserializeOwned,
    Resp: Serialize,

Deserialize JSON, run a Handler, serialize the response as JSON.

Transport adapters (for example generated axum routes) use this at the HTTP boundary while keeping handler execution on World via run_handler.