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.

scripts/qa-transit-browser.mjs

@@ -57,6 +57,7 @@ export async function reportTransitVisibility(page, label) {
     const layer = app.dataManager.layers.get('transit').module;
     const state = layer._transitStateForTest();
     return {
+      pageVisibility: document.visibilityState,
       total: state._vehicles.size,
       visible: state._visible.size,
       moving: state._moving.size,
@@ -69,6 +70,10 @@ export async function reportTransitVisibility(page, label) {
     };
   });
   console.log(`  ${label}: ${JSON.stringify(result)}`);
+  if (result.pageVisibility !== 'visible')
+    throw new Error(
+      `${label}: Transit QA requires a visible page; hidden pages deliberately pause polling`,
+    );
   if (result.renderLoop === false || result.renderErrors.length)
     throw new Error(
       `${label}: Cesium render loop stopped or raised an error: ${JSON.stringify(result.renderErrors)}`,