Keep the debug handle off window between engines and recover the page after a failed recovery

The application's debug handle is one object, present on window only while a globe is attached, so scripts reading __godsEyeView?.engine.kind see no null engine mid-switch. A detached application has no live components: settle no longer waits for a frame of a missing engine, and an engine that runs again after a failed recovery hides the loading screen the error showed.

src/app/debugHandleSwitch.test.mjs

@@ -0,0 +1,89 @@
+// The debug handle is one object for the page; it is on window only while a
+// globe is attached, as when every engine built its own application, so
+// scripts reading `__godsEyeView?.engine.kind` never see a null engine.
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { createApplicationTools } from './tools.js';
+import { createSceneHost } from './sceneHost.js';
+import { createFakeEngine } from '../globe/testing/fakeEngine.js';
+import { _resetRenderGovernorForTest } from '../renderGovernor.js';
+
+test('the debug handle leaves window between engines and comes back the same', async (t) => {
+  const saved = {
+    window: globalThis.window,
+    document: globalThis.document,
+    localStorage: globalThis.localStorage,
+  };
+  globalThis.window = {};
+  globalThis.localStorage = {
+    getItem: () => null,
+    setItem() {},
+    removeItem() {},
+  };
+  globalThis.document = {
+    hidden: false,
+    getElementById: () => null,
+    querySelector: () => null,
+    body: {
+      classList: { add() {}, remove() {}, toggle() {}, contains: () => false },
+      appendChild() {},
+    },
+    addEventListener() {},
+    removeEventListener() {},
+  };
+  t.after(() => {
+    _resetRenderGovernorForTest();
+    for (const [name, value] of Object.entries(saved)) {
+      if (value === undefined) delete globalThis[name];
+      else globalThis[name] = value;
+    }
+  });
+  const sceneHost = createSceneHost();
+  const navara = (kind) => ({
+    kind,
+    viewer: null,
+    engine: createFakeEngine({ kind, canvas: new EventTarget() }),
+    tileset: null,
+    mapStackController: { kind: 'maps' },
+    operations: { surface: {} },
+  });
+  let current = navara('navara');
+  await sceneHost.attach(current);
+  const scene = {
+    operations: { surface: {} },
+    sceneHost,
+    current: () => current,
+  };
+  const cleanups = [];
+  await createApplicationTools({
+    scene,
+    voice: {
+      createControl: () => ({ update() {}, on: () => () => {}, remove() {} }),
+      createCard: () => null,
+      createSession: () => ({
+        async start() {},
+        stop() {},
+        sendText() {},
+        sendMapEvent() {},
+      }),
+    },
+    controls: { styleManager: {}, weatherEffects: null },
+    data: {
+      dataManager: { layers: new Map(), getAll: () => [] },
+      presentation: { flushVisible() {} },
+    },
+    signal: new AbortController().signal,
+    defer: (dispose) => cleanups.push(dispose),
+  });
+  const handle = window.__godsEyeView;
+  assert.equal(handle.engine, current.engine);
+  await sceneHost.detach({ handoff: true });
+  assert.equal(window.__godsEyeView, undefined);
+  assert.equal(handle.engine, null);
+  current = navara('navara');
+  await sceneHost.attach(current);
+  assert.equal(window.__godsEyeView, handle);
+  assert.equal(handle.engine, current.engine);
+  while (cleanups.length) await cleanups.pop()();
+  assert.equal(window.__godsEyeView, undefined);
+});

src/app/tools.js

@@ -162,7 +162,8 @@ export async function createApplicationTools({
     { defer },
   );
 
-  // The application's debug handle; its globe fields follow the engine.
+  // The application's debug handle, the same object on every globe; its
+  // globe fields follow the engine.
   const debug = {
     viewer: null,
     engine: null,
@@ -179,7 +180,6 @@ export async function createApplicationTools({
     surfaceServices: operations.surface,
     requestRender: governorRequestRender,
   };
-  window.__godsEyeView = debug;
   defer(() => {
     if (window.__godsEyeView === debug) delete window.__godsEyeView;
   });
@@ -232,8 +232,12 @@ export async function createApplicationTools({
           cockpitCloudEffects: controls.cockpitCloudEffects ?? null,
           voiceCommands: attached.voiceCommands,
         });
+        // Present only while a globe is attached, as when every engine
+        // built its own application: scripts read `engine.kind` from it.
+        window.__godsEyeView = debug;
       },
       detachScene() {
+        if (window.__godsEyeView === debug) delete window.__godsEyeView;
         Object.assign(debug, {
           viewer: null,
           engine: null,

src/main.js

@@ -91,10 +91,12 @@ function createApplication(kind, engineSwitch) {
   return application;
 }
 
+// The running application while a globe is attached to it; null while the
+// page has no engine (between engines, or after a failed recovery).
 function liveComponents() {
-  return application?.getState().status === 'ready'
+  if (application?.getState().status !== 'ready') return null;
-    ? application.getComponents()
+  const components = application.getComponents();
-    : null;
+  return components.scene?.engine ? components : null;
 }
 
 // The page's application is created once; a switch detaches and attaches
@@ -108,7 +110,7 @@ const legacySwitch =
 // parked for a later switch back.
 async function leave(from) {
   const components = liveComponents();
-  const attached = Boolean(components?.scene.engine);
+  const attached = Boolean(components);
   if (attached) {
     cover ??= keepGlobeFrame(components.scene.engine);
     cockpit = components.controls.styleManager.getCockpitState();
@@ -206,6 +208,9 @@ async function settle() {
   layerSession.handoffLayers = null;
   cockpit = null;
   withdrawEngineRetry();
+  // An engine runs again after a failed recovery showed its error: the
+  // application, built once, does not start its loading chrome again.
+  loading.classList.add('hidden');
   // The running engine owns the address again, including an entry visited
   // before its share link listened or while it was held.
   components.controls.styleManager.shareLinkManager?.resumeNavigation?.();