Function reload_config 

async fn reload_config(__arg0: State<Arc<SharedState>>) -> impl IntoResponse

POST /api/config/reload — re-reads gateway.yaml from disk (with env interpolation), recompiles all route graphs, and swaps them in. Returns {"status": "reloaded"} on success.

Errors: 500 Internal Server Error if no config path is set or the file fails to parse/validate/compile; the running config is left unchanged.