Let the app run under a panel page's document base

A panel page loads the app with <base> pointing at the app's server, so
addresses the app builds resolve against the document base instead of
the page location, and hash updates stay on the page's own address.
The dev server answers panel origins with CORS on the API routes too.

build/vite.js

@@ -8,6 +8,39 @@ export const PANEL_CORS_ORIGINS = Object.freeze([
   /^https:\/\/[a-z0-9]+\.claudemcpcontent\.com$/,
 ]);
 
+/**
+ * Vite plugin answering cross-origin reads from PANEL_CORS_ORIGINS on every
+ * path. It runs ahead of the API middlewares, which Vite's own `cors` option
+ * would not cover.
+ */
+function panelCorsPlugin() {
+  const install = (server) => {
+    server.middlewares.use((req, res, next) => {
+      const origin = req.headers.origin;
+      if (
+        !origin ||
+        !PANEL_CORS_ORIGINS.some((allowed) => allowed.test(origin))
+      )
+        return next();
+      res.setHeader('Access-Control-Allow-Origin', origin);
+      res.setHeader('Vary', 'Origin');
+      if (req.method !== 'OPTIONS') return next();
+      res.setHeader('Access-Control-Allow-Methods', 'GET, HEAD, POST, OPTIONS');
+      res.setHeader(
+        'Access-Control-Allow-Headers',
+        req.headers['access-control-request-headers'] || '',
+      );
+      res.statusCode = 204;
+      res.end();
+    });
+  };
+  return {
+    name: 'panel-cors',
+    configureServer: install,
+    configurePreviewServer: install,
+  };
+}
+
 /** Build browser assets with explicit inputs; never load environment or providers. */
 export function createBrowserViteConfig({
   plugins = [],
@@ -20,6 +53,7 @@ export function createBrowserViteConfig({
 } = {}) {
   return {
     plugins: [
+      panelCorsPlugin(),
       cesium(),
       applicationHtmlPlugin(),
       ...plugins,
@@ -52,7 +86,7 @@ export function createBrowserViteConfig({
       },
       // Cross-origin reads: local pages, as Vite allows by default, plus the
       // MCP Apps panels that load the app into a conversation (Claude's
-      // sandbox origins). Development and preview only.
+      // sandbox origins); see panelCorsPlugin. Development and preview only.
       cors: { origin: PANEL_CORS_ORIGINS },
       // These headers protect the document containing Provider Settings.
       // Embed-mode documents are framable instead; see embed-framing.js.

src/data/aisLiveVessels.js

@@ -5,6 +5,9 @@ import { createAisStreamSource } from '../sources/live/standalone.js';
 const aisLiveVesselsLayer = createApplicationVessels({
   source: createAisStreamSource({
     apiUrl: import.meta.env?.VITE_AIS_LIVE_API_URL || '/api/ais-live',
+    // The app's server, also when a panel page loads the app under <base>.
+    origin: () =>
+      new URL(globalThis.document?.baseURI ?? 'http://localhost').origin,
   }),
   options: {
     maxRows: import.meta.env?.VITE_AIS_LIVE_MAX_ROWS,

src/keySetup.js

@@ -318,7 +318,11 @@ export async function initKeySetup({
               globalThis.location?.hash?.slice(1) || '',
             );
             if (next !== null)
-              globalThis.history?.replaceState?.(null, '', `#${next}`);
+              globalThis.history?.replaceState?.(
+                null,
+                '',
+                new URL(`#${next}`, globalThis.location.href).href,
+              );
           } catch {
             // Continuity is a nicety, never a blocker.
           }

src/reasonableDefaults.test.mjs

@@ -61,7 +61,7 @@ function uiBlock(start, end) {
 /** A ShareLinkManager over a synthetic hash — enough surface for parseInitialHash. */
 function managerForHash(hash) {
   globalThis.window = { location: { hash, href: `http://localhost/${hash}` } };
-  globalThis.history = { replaceState(_s, _t, next) { window.location.hash = next; } };
+  globalThis.history = { replaceState(_s, _t, next) { window.location.hash = new URL(next, window.location.href).hash; } };
   const viewer = {
     camera: {
       changed: { addEventListener() {} },

src/sharelink.celestial.test.mjs

@@ -34,8 +34,8 @@ function assertClaimsBefore(block, mutation, label) {
 function makeManager(hash = '') {
   globalThis.window = { location: { hash, href: `http://localhost/${hash}` } };
   globalThis.history = {
-    replaceState(_state, _title, nextHash) {
-      window.location.hash = nextHash;
+    replaceState(_state, _title, next) {
+      window.location.hash = new URL(next, window.location.href).hash;
     },
   };
   const viewer = {

src/sharelink.js

@@ -529,7 +529,13 @@ export class ShareLinkManager {
     if (this._destroyed || this._initialRestorePending) return;
     const params = this._buildHashParams();
     if (!params) return;
-    history.replaceState(null, '', `#${params.toString()}`);
+    // The hash belongs to this page's address, not the document base the
+    // app may load under.
+    history.replaceState(
+      null,
+      '',
+      new URL(`#${params.toString()}`, window.location.href).href,
+    );
   }
 
   /** Build a deterministic snapshot without mutating history. */

src/standalone/layerSources.js

@@ -29,6 +29,9 @@ export function createStandaloneLayerSources() {
     military: createAdsbLolSource(),
     vessels: createAisStreamSource({
       apiUrl: import.meta.env?.VITE_AIS_LIVE_API_URL || '/api/ais-live',
+      // The app's server, also when a panel page loads the app under <base>.
+      origin: () =>
+        new URL(globalThis.document?.baseURI ?? 'http://localhost').origin,
     }),
     cctv: createCctvSource(),
     radio: createRadioSource(),

src/standalone/toolCatalog.js

@@ -16,7 +16,7 @@ export function loadToolCatalog() {
           tools: coreTools,
           services: createToolServices({
             fetchImpl: (...args) => globalThis.fetch(...args),
-            appUrl: globalThis.location.origin,
+            appUrl: new URL(globalThis.document.baseURI).origin,
           }),
         }),
         'voice',

src/standalone/tools.js

@@ -8,7 +8,7 @@ export function createStandaloneTools(options) {
     sceneDataPacks: {
       sources: {
         assets: createAssetDirectorySource({
-          baseUrl: new URL('/scene-assets/', window.location.href).href,
+          baseUrl: new URL('/scene-assets/', document.baseURI).href,
         }),
       },
     },

src/tooling/viteBuild.test.mjs

@@ -12,7 +12,8 @@ test('explicit build inputs preserve browser-only defines, plugin order and loop
     googleApiKey: 'browser-fixture',
     cesiumToken: 'ion-fixture',
   });
-  assert.equal(config.plugins[2], plugin);
+  assert.equal(config.plugins[0].name, 'panel-cors');
+  assert.equal(config.plugins[3], plugin);
   assert.equal(config.server.host, 'localhost');
   assert.equal(config.server.port, 4173);
   assert.deepEqual(config.server.allowedHosts, [
@@ -42,6 +43,40 @@ test('explicit build inputs preserve browser-only defines, plugin order and loop
   );
 });
 
+test('panel origins may read every dev server path, other sites may not', () => {
+  let middleware;
+  createBrowserViteConfig().plugins[0].configureServer({
+    middlewares: { use: (fn) => (middleware = fn) },
+  });
+  const request = (origin, method = 'GET') => {
+    const headers = {};
+    let ended = false;
+    let passed = false;
+    middleware(
+      { method, headers: origin ? { origin } : {} },
+      {
+        setHeader: (name, value) => (headers[name] = value),
+        end: () => (ended = true),
+      },
+      () => (passed = true),
+    );
+    return { headers, ended, passed };
+  };
+  const panel = request('https://abc123.claudemcpcontent.com');
+  assert.equal(
+    panel.headers['Access-Control-Allow-Origin'],
+    'https://abc123.claudemcpcontent.com',
+  );
+  assert.equal(panel.passed, true);
+  assert.equal(
+    request('https://abc123.claudemcpcontent.com', 'OPTIONS').ended,
+    true,
+  );
+  const other = request('https://example.com');
+  assert.deepEqual(other.headers, {});
+  assert.equal(other.passed, true);
+});
+
 test('build helper does not discover environment values or construct local providers', () => {
   const before = process.env.GOOGLE_MAPS_API_KEY;
   process.env.GOOGLE_MAPS_API_KEY = 'environment-fixture';
@@ -52,7 +87,7 @@ test('build helper does not discover environment values or construct local provi
       undefined,
     );
     assert.deepEqual(
-      config.plugins.slice(2).map((plugin) => plugin.name),
+      config.plugins.slice(3).map((plugin) => plugin.name),
       ['embed-framing'],
     );
   } finally {
@@ -66,7 +101,7 @@ test('root config retains existing named exports and standalone provider order',
     assert.equal(compatibility[name], value, name);
   const config = standaloneConfig({ mode: 'test' });
   assert.deepEqual(
-    config.plugins.slice(2, -3).map((plugin) => plugin.name),
+    config.plugins.slice(3, -3).map((plugin) => plugin.name),
     providers.localProviderPlugins().map((plugin) => plugin.name),
   );
   assert.equal(config.plugins.at(-4).name, 'gev-key-setup');