Function custom_cgroup_no_ctrl_task_migration 

pub fn custom_cgroup_no_ctrl_task_migration(
    ctx: &Ctx<'_>,
) -> Result<AssertResult>

Workers ping-pong between cg_mobile and cg_1 across 9 MoveAllTasks phases.

All three cgroups persist for the scenario (the MoveAllTasks ops reference them by name across every Step), so they live in the Backdrop. cg_1 is an empty move target declared via Backdrop::push_op so it never spawns its own workers — only the cg_mobile handle ping-pongs between cg_mobile and cg_1. Workers that Op::MoveAllTasks transfers into a Backdrop cgroup retain their Backdrop ownership so the persistent workers survive every step teardown.