Function plan_delete 

pub fn plan_delete<F>(
    schema: &Schema,
    table_name: &str,
    pk: &str,
    find_children: F,
) -> Result<DeletePlan, PlannerError>
where
    F: Fn(&Table, &ForeignKey, &str) -> Vec<(String, String)>,

Plan the deletion of a single row identified by its table and primary key.

The plan does not interact with storage; callers supply child row lookup via the find_children closure. This keeps the core crate storage-agnostic.