Function spawn_tracked 

pub fn spawn_tracked(
    block_id: &str,
    cmd: &mut Command,
    join: Join,
) -> Result<Child>

Spawn cmd for block_id already inside the block’s tracker, so nothing it starts can escape between spawn and assignment: on Linux it joins the cgroup before exec (place_spawn); on Windows it starts suspended, is assigned to the job, then resumed. The one way an agent-side tokio spawn should start (the Codex App Server, which spawns internally, uses place_spawn and track_spawned_agent).