Status: IN
Leaf pages carry a `next_sibling` field in their serialized format (`NO_SIBLING = 0xFFFFFFFF` sentinel), but no tree operation uses sibling pointers for traversal or merging — it is scaffolding, not a live data structure. Note: may refine existing `btree-leaf-sibling-chain`.
Source: entries/2026/05/28/topic-concurrent-btree-deletion.md