perf: reduce mobile rendering and cull offscreen characters and building tiles

tests/frame-clock.test.ts

@@ -0,0 +1,24 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { createFrameClock } from '../src/scene/frameClock.ts';
+
+test('30 fps pacing retains elapsed simulation time on 60 and 120 Hz displays', () => {
+  for (const hz of [60, 120]) {
+    const clock = createFrameClock(30);
+    let frames = 0, elapsed = 0;
+    for (let i = 0; i <= hz * 10; i++) {
+      const delta = clock.tick(i * 1000 / hz);
+      if (delta !== undefined) { frames++; elapsed += delta; }
+    }
+    assert.equal(frames, 301);
+    assert.ok(Math.abs(elapsed - 10) < 1e-8);
+  }
+});
+
+test('resume resets elapsed time instead of simulating the hidden interval', () => {
+  const clock = createFrameClock(30);
+  clock.tick(0); clock.tick(100);
+  clock.reset();
+  assert.equal(clock.tick(60000), 0);
+  assert.equal(clock.tick(60001), undefined);
+});