Leave the scope mask off a globe whose container holds no DOM children

src/scopeMask.js

@@ -454,7 +454,8 @@ function globeOf(target) {
 export function installScopeMask(target) {
   if (_canvas) return;
   const globe = globeOf(target);
-  if (!globe.container) return;
+  // Only a DOM container can hold the mask (an engine double's cannot).
+  if (typeof globe.container?.appendChild !== 'function') return;
   syncScopeMaskAppearance();
   _container = globe.container;
   _globe = globe;

src/scopeMask.test.mjs

@@ -801,3 +801,11 @@ test('on a globe engine (Navara) the mask goes into its host container and follo
     dom.restore();
   }
 });
+
+test('an engine without a DOM container gets no mask and no listeners', async () => {
+  const { createFakeEngine } = await import('./globe/testing/fakeEngine.js');
+  const engine = createFakeEngine({ kind: 'navara' });
+  installScopeMask(engine);
+  assert.equal(engine.frames.preRender.numberOfListeners, 0);
+  destroyScopeMask();
+});