Function walk_tree_integrity 

pub fn walk_tree_integrity<S, V>(
    source: &S,
    roots: impl IntoIterator<Item = ContentHash>,
    visitor: &mut V,
) -> Result<(), HeddleError>
where
    S: ObjectSource + ?Sized,
    V: FnMut(TreeIntegrityEvent<'_>) -> Result<(), HeddleError>,

Walk all trees reachable from roots, deduplicating visited trees.

Missing root or subtree trees emit TreeIntegrityEvent::MissingTree. Gitlink entries are not descended into. Visitation order is depth-first, sorted tree entry order. The implementation uses explicit frames so tree depth cannot overflow the process stack.