Structural sharing.

A CHAMP is a persistent map: updating it returns a new version while the old one stays valid and unchanged. It does this by sharing — a new version copies only the nodes on the path from the root to the change, and points at every untouched subtree the old version already held. A snapshot, then, is the old root kept; taking one costs nothing.

The node layout is what keeps the sharing tight. Each node carries two 32-bit bitmaps over one compact tuple — a datamap marking inline key-value pairs and a nodemap marking child nodes — with five-bit fragments of the hash driving 32-way branching down a handful of levels. A change rewrites a short spine of small nodes, not the map; the rest is reused by reference.

Codemojex wants this every time it shows or rewinds a game. A snapshot of a room for a spectator, a round preserved for replay, an undo of the last move — each is a cheap new root over a shared structure, not a copy of the board. The old state remains exactly itself, which is what makes versioning and broadcast affordable.