Function proxy 

pub async fn proxy(
    cfg: &GatewayConfig,
    handle: &str,
    arguments: Map<String, Value>,
    project_root: &str,
) -> Result<String, String>

Proxy a server::tool call to its owning downstream server.

project_root is the caller’s project root, forwarded to the output post-processor so L3 consolidation (#1095) can index the result into the project’s stores. Empty disables project-scoped indexing.