Function list_items 

pub async fn list_items(
    project_dir: &Path,
    filter: &ListFilter,
) -> Result<Vec<BacklogItem>>

Return PBIs from project_dir in canonical hierarchical priority order.

Items are grouped as a parent/child forest: roots in ascending rank order, each parent immediately followed by its subtree (siblings in rank order). A filtered-out or absent parent promotes its children to roots, so the tree is cut cleanly at the filter boundary. See crate::service::hierarchical_order.

Apply only the conditions specified by filter. Return Error::NotInitialized for an uninitialized board. When filter.roots_only is set, items with a persisted parent link remain excluded even if that parent is outside the filtered result.