Merge main and switch Cesium and Navara in place through Vue

Preserve the camera, map source and layer selection across engine sessions. Restore the previous engine if startup fails and retain local history navigation.

src/app/application.test.mjs

@@ -31,6 +31,8 @@ test('importing and constructing the package is inactive without browser globals
   const result = spawnSync(
     process.execPath,
     [
+      // Views are single-file components; Node needs the loader hosts use.
+      '--import=gods-eye-view/build/register-vue',
       '--input-type=module',
       '-e',
       `
@@ -245,6 +247,17 @@ test('the separate viewer export imports without constructing a browser viewer',
   assert.throws(() => createApplicationViewer({}), /containers are required/);
 });
 
+test('the viewer gets the starry sky as an option, which keeps the Sun and Moon', async () => {
+  const { applicationViewerOptions } = await import('./viewer.js');
+  const { StarrySky } = await import('../sky/starrySky.js');
+  const creditContainer = {};
+  const options = applicationViewerOptions(creditContainer);
+  // CesiumWidget skips scene.sun and scene.moon when skyBox is false.
+  assert.ok(options.skyBox instanceof StarrySky);
+  assert.equal(options.creditContainer, creditContainer);
+  options.skyBox.destroy();
+});
+
 function pinchFixture({ zoomEventTypes } = {}) {
   const handlers = new Set();
   const relayed = [];