Harden gameplay timing and map loading

tests/round-clock.test.ts

@@ -0,0 +1,20 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { roundClock } from "../shared/round-clock";
+
+test("round timer accounts for return latency and stops at the server deadline", () => {
+  const clock = roundClock(100000, 1000, 5000);
+  const deadline = new Date(105000).toISOString();
+  assert.equal(clock.remaining(deadline, 5000), 3);
+  assert.equal(clock.remaining(deadline, 7001), 1);
+  assert.equal(clock.remaining(deadline, 8000), 0);
+  assert.equal(clock.remaining(deadline, 9000), 0);
+});
+
+test("round timer relies on elapsed time even if the device wall clock changes", (t) => {
+  const clock = roundClock(100000, 1000, 1000);
+  t.mock.method(Date, "now", () => -10000000);
+  assert.equal(clock.remaining(new Date(110000).toISOString(), 5000), 6);
+  t.mock.method(Date, "now", () => 10000000);
+  assert.equal(clock.remaining(new Date(110000).toISOString(), 11000), 0);
+});