Function deploy 

pub fn deploy(
    config: &FleetConfig,
    target_nodes: &[String],
    action: DeployAction,
    max_parallel: usize,
    use_builders: bool,
) -> Result<DeployReport>

Run the full deployment pipeline using the DAG executor.

Each host progresses independently through eval → build → copy → activate, with per-stage concurrency limits. A host that fails at any stage is cancelled for subsequent stages without blocking other hosts.