refactor: move world concepts into engine

tests/actors.test.ts

@@ -0,0 +1,38 @@
+import { expect, test } from "bun:test"
+import { Actor, type Actor as RuntimeActor, type ActorDefinition } from "../engine/scene/Actor"
+
+type World = { updates: string[] }
+
+const numberDefinition: ActorDefinition<{ value: number }, World> = {
+  prototype: { groups: [], radius: 1, minY: 0, maxY: 1 },
+  update: (state, _dt, world) => {
+    state.value++
+    world.updates.push(String(state.value))
+  },
+  transform: (state) => ({ x: state.value, y: 0, z: 0, heading: 0, scale: 1 }),
+}
+
+const textDefinition: ActorDefinition<{ value: string }, World> = {
+  prototype: { groups: [], radius: 1, minY: 0, maxY: 1 },
+  update: (state, _dt, world) => {
+    state.value += "!"
+    world.updates.push(state.value)
+  },
+  transform: (state) => ({ x: state.value.length, y: 0, z: 0, heading: 0, scale: 1 }),
+}
+
+test("one actor collection safely erases unrelated state types", () => {
+  const actors: RuntimeActor<World>[] = [
+    Actor.create(numberDefinition, { value: 1 }),
+    Actor.create(textDefinition, { value: "a" }),
+  ]
+  const world: World = { updates: [] }
+
+  for (const actor of actors) {
+    Actor.update(actor, 1, world)
+  }
+
+  expect(world.updates).toEqual(["2", "a!"])
+  expect(Actor.transform(actors[0]).x).toBe(2)
+  expect(Actor.transform(actors[1]).x).toBe(2)
+})