test(engine): add tick loop + game determinism integration test

src/engine/__tests__/determinism.test.ts

@@ -0,0 +1,44 @@
+import { describe, expect, it } from 'vitest';
+import { buildContent } from '../../content/schema';
+import { createGameState, startAction, tickGame } from '../game';
+import { advance, createTickLoop, TICK_MS } from '../tickLoop';
+
+function testContent() {
+  return buildContent({
+    resources: [{ id: 'gold', name: 'Gold', startAmount: 0 }],
+    actions: [
+      {
+        id: 'forage',
+        name: 'Forage',
+        durationMs: 300,
+        yields: { resourceId: 'gold', amount: 1 },
+      },
+    ],
+  });
+}
+
+function simulate(elapsedMs: number, chunkMs: number) {
+  const content = testContent();
+  const state = createGameState(content);
+  startAction(state, content, 'forage');
+
+  const loop = createTickLoop({ tickMs: TICK_MS, startNow: 0 });
+  let now = 0;
+  while (now < elapsedMs) {
+    const next = Math.min(now + chunkMs, elapsedMs);
+    advance(loop, next, () => {
+      tickGame(state, content, TICK_MS);
+    });
+    now = next;
+  }
+  return { tickCount: loop.tickCount, gold: state.resources.gold };
+}
+
+describe('determinism integration', () => {
+  it('produces identical tick counts and game state regardless of advance chunking', () => {
+    const whole = simulate(5000, 5000);
+    const chunked = simulate(5000, 37);
+    expect(chunked.tickCount).toBe(whole.tickCount);
+    expect(chunked.gold).toBe(whole.gold);
+  });
+});