Constant ENV_FULL_CLUSTER_JSON 

pub const ENV_FULL_CLUSTER_JSON: &str = "FLODL_INTERNAL_FULL_CLUSTER_JSON";

Env var name carrying the full multi-host topology (hex-encoded JSON of ClusterConfig). Set by fdl-cli on its own process env so the spawned user binary inherits it and detects launcher role. Mirrors flodl::distributed::launcher::ENV_FULL_CLUSTER_JSON.