Function serve 

pub async fn serve<R: ConnectionRouter>(
    config: GatewayConfig,
    identity: Identity,
    build: impl FnOnce(&RuntimeHandle) -> R,
) -> Result<()>

Bind, create shards, and serve, in one call.

The shape most composition binaries want. build runs after the sockets are bound and before the first connection is accepted, which is the only window in which “the initial shards exist before anyone can be routed to one” is guaranteed.

Errors

Whatever Gateway::bind or Gateway::serve report.