Delta encoding multiplayer game state

Old Light is a browser strategy game where a tab can stay open for days. The client holds a full copy of the galaxy state it is allowed to see, and the server keeps that copy honest by sending patches: every change arrives as a world.delta message the client merges into what it already has. Sending changes instead of resending state is textbook delta encoding. What that leaves open is what a game state patch actually holds, and why the patch a rival receives is not the one you receive. I covered how the stream starts (one snapshot on connect, then deltas) and the time-math traps inside it in the networking post. This post is about the delta itself. What goes in a game state patch When people say delta encoding they usually mean byte diffs: compare two versions of a blob, ship the difference. That requires the sender to know which version the receiver holds. A game server broadcasting to thousands of sockets can't afford that; tracking a per-client "last known state" and di