Function run 

pub fn run(
    target: &Target,
    plan: Plan,
    cancellation: &CancellationToken,
    observer: &mut (impl Observer + ?Sized),
) -> Result<Done, Broken>

Synchronous owner of CPU workers. Phase callbacks run on the caller, with workers gated before start and fully drained before finish. No process-global signal handler is installed. Caller cancellation never detaches owned work.