Function run_json_handler_function 

pub fn run_json_handler_function<F, Req, Resp, Params>(
    f: F,
    handler_name: &'static str,
    json_body: &str,
    world: &mut World,
) -> Result<String, String>
where
    F: IntoHandler<Req, Resp, Params>,
    Req: DeserializeOwned + 'static,
    Resp: Serialize + 'static,

JSON boundary helper for any function that implements IntoHandler.

Builds a fresh boxed handler from f each call (same cost model as per-request into_handler in generated glue). When f is a concrete function item, Req, Resp, and Params are inferred from its type.

Generated axum routes use the #[handler]-emitted {name}__galeon_axum_json shim for handlers with ECS SystemParam extras, because bare .into_handler(...) on a function path often cannot infer Params.