Check that a running mission replay survives an engine switch

The session test now switches engines in both directions with the replay
running, paused and resumed, and checks it stays active, unpaused and
advancing.

src/standalone/sessionSwitch.test.mjs

@@ -74,6 +74,8 @@ async function fixture(t, { aircraft = null, failOpen = false } = {}) {
   };
   const engines = [];
   const newEngine = (kind) => {
+    const retained = engines.find((engine) => engine.kind === kind);
+    if (retained) return retained;
     const engine = createFakeEngine({
       kind,
       container: document.createElement('div'),
@@ -250,6 +252,46 @@ test('Space Missions keeps its context, selection and paused replay across engin
   }
 });
 
+test('Space Missions keeps a running replay advancing across engines', async (t) => {
+  const f = await fixture(t);
+  assert.equal((await f.context.setContextMode('space-missions')).ok, true);
+  const launches = f.catalog.get('rocket-launches');
+  launches.selectMissionAt(0);
+  launches.setReplaySpeed(4);
+  launches.startSelectedReplay();
+  f.engine().camera.completeFlight();
+  await flushLifecycleTasks(t, 16_000);
+  f.engine().fake.frame();
+  launches.toggleReplayPause();
+  f.address({
+    enabledLayerIds: ['rocket-launches', 'satellites'],
+    options: {},
+  });
+  for (const kind of ['cesium', 'navara']) await f.switcher.select(kind);
+  launches.toggleReplayPause();
+  await flushLifecycleTasks(t, 100);
+  f.engine().fake.frame();
+  for (const kind of ['cesium', 'navara']) {
+    const before = launches.qaDrawn();
+    assert.ok(before.replay.active);
+    assert.equal(before.paused, false);
+    assert.ok(before.replay.phaseProgress > 0);
+    await f.switcher.select(kind);
+    const after = launches.qaDrawn();
+    assert.ok(after.replay.active);
+    assert.equal(after.paused, false);
+    await flushLifecycleTasks(t, 500);
+    f.engine().fake.frame();
+    const advanced = launches.qaDrawn();
+    assert.ok(advanced.replay.active);
+    assert.equal(advanced.paused, false);
+    assert.ok(
+      advanced.replay.phaseProgress > before.replay.phaseProgress,
+      'a running replay advances on the incoming engine',
+    );
+  }
+});
+
 for (const aircraft of ['flights', 'military']) {
   test(`failed engine startup restores the ${aircraft} cockpit and session without history`, async (t) => {
     const f = await fixture(t, { aircraft, failOpen: true });