Rules run by both client and server live in core¶
Any rule that both the client and the server evaluate (movement, AABB physics, chunk generation, block properties,
ability costs shown to the player) lives once in the Kotlin Multiplatform core module and is compiled into both
the JVM server and the Wasm client. Any value the server can tune at runtime reaches the client as data (for example
in Welcome or a config sync message), and the client never hardcodes it. Duplicated rules and constants have
repeatedly drifted apart and broken Prediction, so this is strict, even for a few lines.
Consequences¶
- Player movement runs through
corePlayerKinematics.step():MovementProcessorand the client Prediction are adapters over aBlockQuery, and gravity / jump / fly speeds reach the client asKinematicTuninginWelcomeandGameConfigSync. Only what counts as solid differs: the client does not see occupied entities. - A TypeScript UI never re-implements a game rule; it asks Kotlin/
coreor the server.