Module btree 

CoW B+ tree engine. Mutations clone pages; old pages go to pending-free list.

Structs

BTree

B+ tree metadata. Lightweight struct - pages are stored externally.

Functions

cow_page

CoW a page. No-op if already owned by this txn. In-place mode reuses page ID.

propagate_cow_up

Propagate CoW up through ancestors (no split, just update child pointers).