Status: IN
B-tree sequential access is strictly forward-only: iteration descends the left spine (following children at index zero at every internal level) to reach the leftmost leaf, then walks the forward-only sibling chain, with no backward pointer, reverse iterator, or random leaf access mechanism.
Both the descent path and horizontal walk are unidirectional, constraining all sequential access to forward traversal
Depends on (SL): btree-leaf-sibling-chain-forward-only, iter-descends-left-spine