Run the worker prelude ahead of Cesium's own workers script

Cesium's script sets CESIUM_WORKERS itself when it loads, so the panel's
combined workers script was never used, and neither was the embedded
terrain-heights file: the worker still requested it from the panel
page's site. The panel build now writes only the prelude, and the panel
puts it ahead of whatever Cesium assigns to CESIUM_WORKERS. The separate
esbuild bundle of Cesium's workers is gone.

src/app/globePanelRuntime.js

@@ -489,14 +489,25 @@ export function panelRuntime(config) {
       'text/html',
     );
     window.CESIUM_BASE_URL = `${config.panelBase}cesium/`;
-    const [workers] = await Promise.all([
-      appFetch(config.panelBase + config.workersPath).then((r) => r.text()),
+    const [prelude] = await Promise.all([
+      appFetch(config.panelBase + config.workerPreludePath).then((r) =>
+        r.text(),
+      ),
       ...[...built.head.querySelectorAll('link[rel="stylesheet"]')].map(
         (link) => addStylesheet(link.getAttribute('href')),
       ),
     ]);
-    // Cesium starts its workers from this script instead of from files.
-    window.CESIUM_WORKERS = workers;
+    // Cesium's script sets CESIUM_WORKERS, its workers as one script it
+    // starts from memory. Workers request files themselves, which this page
+    // cannot answer, so the prelude, holding those files, runs ahead of it.
+    let workers;
+    Object.defineProperty(window, 'CESIUM_WORKERS', {
+      configurable: true,
+      get: () => workers,
+      set: (script) => {
+        workers = prelude + script;
+      },
+    });
     // Images in the markup load their files once added; give them the
     // files instead of letting them request this page's site.
     const images = [];

src/tooling/panelBuild.test.mjs

@@ -6,16 +6,18 @@ import test from 'node:test';
 import * as PANEL_PATHS from '../tools/globePanel.js';
 import {
   PANEL_BASE,
-  PANEL_WORKERS_PATH,
+  PANEL_WORKER_PRELUDE_PATH,
   panelBuildConfig,
   panelBuildPlugin,
   workerFilesPrelude,
-  workersEntrySource,
 } from '../../build/panel.js';
 
 test('the panel loads the paths the panel build writes', () => {
   assert.equal(PANEL_BASE, PANEL_PATHS.PANEL_BASE);
-  assert.equal(PANEL_WORKERS_PATH, PANEL_PATHS.PANEL_WORKERS_PATH);
+  assert.equal(
+    PANEL_WORKER_PRELUDE_PATH,
+    PANEL_PATHS.PANEL_WORKER_PRELUDE_PATH,
+  );
 });
 
 test('the panel build is one script and one stylesheet under /panel/', () => {
@@ -30,19 +32,6 @@ test('the panel build is one script and one stylesheet under /panel/', () => {
   assert.equal(config.build.chunkSizeWarningLimit, 1500);
 });
 
-test("Cesium's workers load lazily from one script", () => {
-  const source = workersEntrySource(['createGeometry', 'decodeDraco'], '/w');
-  assert.match(source, /^self\.CesiumWorkers = \{/);
-  assert.match(
-    source,
-    /"createGeometry": \(\) => import\("\/w\/createGeometry\.js"\)/,
-  );
-  assert.match(
-    source,
-    /"decodeDraco": \(\) => import\("\/w\/decodeDraco\.js"\)/,
-  );
-});
-
 test('the dev server serves the panel build and nothing outside it', async () => {
   const root = await mkdtemp(join(tmpdir(), 'panel-build-'));
   try {

src/tools/globePanel.js

@@ -9,8 +9,8 @@
 export const GLOBE_PANEL_URI = 'ui://gods-eye-view/globe';
 /** Where the app's server serves its panel build (see build/panel.js). */
 export const PANEL_BASE = '/panel/';
-/** Cesium's workers as one script, relative to the panel build. */
-export const PANEL_WORKERS_PATH = 'cesium/workers.js';
+/** The script the panel runs ahead of Cesium's workers, in the build. */
+export const PANEL_WORKER_PRELUDE_PATH = 'cesium/worker-prelude.js';
 
 /**
  * Sites the app's browser code loads from directly: map imagery, 3D tiles,
@@ -63,7 +63,7 @@ function panelHtml(runtime) {
     panelHeight: PANEL_HEIGHT_PX,
     protocolVersion: MCP_APPS_PROTOCOL_VERSION,
     toolName: PANEL_REQUEST_TOOL,
-    workersPath: PANEL_WORKERS_PATH,
+    workerPreludePath: PANEL_WORKER_PRELUDE_PATH,
   };
   const script = `(${runtime})(${JSON.stringify(config)});`.replace(
     /<\/script/gi,