Function detached_scope 

pub fn detached_scope(
    parent_generator: Option<ReceiptGenerator>,
) -> Option<ReceiptScope>

Scope for detached work (background delegation): the parent’s generator so the child’s tool results verify against the same key, and a FRESH collector, because the parent’s per-turn collector belongs to a turn that ends before the detached task does. None stays None so receipts-off installs are unchanged.