AlifePlus is a mod for STALKER Anomaly by Damian Sirbu, built on the 2007 X-Ray engine. I went through the source and the architecture is way more serious than you'd expect from a game mod. Here's what's in there. Background STALKER simulates about 2000 NPCs across 30 maps. Most are "offline" — just entries in a graph, no physics or animations. A few hundred near the player are "online" with combat, pathfinding, the works. The engine fires Lua callbacks on events like deaths, zone transitions, and item pickups. AlifePlus hooks into those callbacks and layers a reactive behavior system on top. Pub/sub bus There's a central message bus called xbus . One side has causes — predicates that check world state when a callback fires, then either emit a typed event or return nil. The other side has consequences that subscribe to cause types and run side effects. They don't reference each other and adding a new reaction to an existing cause is one file. BPMN style.…