Status: IN
Page 0 is always the metadata page (root_page, height, total_keys, next_free_page, free_list_head); the root page is never page 0.
Source: entries/2026/05/28/b-tree-storage-engine-btree.md
# Page 0: root_page(4B), height(4B), total_keys(4B), next_free(4B), free_head(4B)
META_FMT = ">5I"
self._f.seek(0)
self._f.write(struct.pack(META_FMT, root, height, total_keys, next_free, free_head))