Load the God's Eye View panel through the MCP server

Hosts serve panels from their own sites and may refuse other addresses;
Codex refuses any address on the user's machine. The panel now never
requests the app's server: it loads the app's panel build and data
through panel_request, a tool only the panel may call, which requests
the path from the app's server. One path in every host; only map
providers load directly.

npm run build:panel writes the panel build to dist/panel, served at
/panel/: one app script, one stylesheet, Cesium's script, and Cesium's
workers as one script Cesium runs from memory. Tools may now be marked
app-only. The panel CORS rules are gone.

src/tools/queries/panelRequest.js

@@ -0,0 +1,184 @@
+/**
+ * The God's Eye View panel's requests. A panel cannot reach the app's server
+ * itself: hosts serve panels from their own sites and may refuse other
+ * addresses, such as a server on the user's machine. The panel asks this
+ * tool instead, which only an app may call, and it requests the path from
+ * the app's server. Large responses come back in parts.
+ */
+
+import { defineTool, ToolError } from '../catalog.js';
+
+/** Bytes of response body per call, before base64. */
+export const PANEL_PART_BYTES = 512 * 1024;
+const HELD_MS = 2 * 60 * 1000;
+const HELD_LIMIT_BYTES = 256 * 1024 * 1024;
+const METHODS = new Set(['GET', 'HEAD', 'POST']);
+// Provider Settings write the app's keys; only the app's own page may.
+const REFUSED_PATHS = [/^\/api\/setup(?:\/|$)/];
+const FORWARDED_REQUEST_HEADERS = ['accept', 'content-type'];
+const DROPPED_RESPONSE_HEADERS = new Set([
+  'connection',
+  'content-encoding',
+  'content-length',
+  'keep-alive',
+  'set-cookie',
+  'transfer-encoding',
+]);
+// Already compressed, so gzip would only cost time.
+const INCOMPRESSIBLE =
+  /^(?:image\/(?!svg)|video\/|audio\/|font\/woff2)|zip|compressed/;
+const COMPRESS_MIN_BYTES = 1024;
+
+// Bodies too large for one call, kept for the calls that read the rest.
+const held = new Map();
+let heldBytes = 0;
+
+function base64(bytes) {
+  let binary = '';
+  for (let start = 0; start < bytes.length; start += 0x8000)
+    binary += String.fromCharCode(...bytes.subarray(start, start + 0x8000));
+  return btoa(binary);
+}
+
+function fromBase64(text) {
+  return Uint8Array.from(atob(text), (char) => char.charCodeAt(0));
+}
+
+async function gzip(bytes) {
+  const stream = new Blob([bytes])
+    .stream()
+    .pipeThrough(new CompressionStream('gzip'));
+  return new Uint8Array(await new Response(stream).arrayBuffer());
+}
+
+function forget(now = Date.now()) {
+  for (const [id, entry] of held) {
+    if (entry.expires > now && heldBytes <= HELD_LIMIT_BYTES) continue;
+    held.delete(id);
+    heldBytes -= entry.bytes.length;
+  }
+}
+
+function part(response, bytes, offset) {
+  const end = Math.min(bytes.length, offset + PANEL_PART_BYTES);
+  return {
+    ...response,
+    offset,
+    body: base64(bytes.subarray(offset, end)),
+    ...(end < bytes.length ? { nextOffset: end } : {}),
+  };
+}
+
+function checkedPath(path) {
+  if (
+    typeof path !== 'string' ||
+    !path.startsWith('/') ||
+    path.startsWith('//')
+  )
+    throw new ToolError('invalid_arguments', 'path must start with one /');
+  const { pathname } = new URL(path, 'http://app.invalid');
+  if (REFUSED_PATHS.some((pattern) => pattern.test(pathname)))
+    throw new ToolError('invalid_arguments', `${pathname} is not available`);
+  return path;
+}
+
+export const panelRequest = defineTool({
+  name: 'panel_request',
+  title: "God's Eye View panel request",
+  description:
+    "Loads a file or data for the God's Eye View panel from the app's " +
+    'server. Only the panel calls this; it does not answer questions.',
+  inputSchema: {
+    type: 'object',
+    properties: {
+      path: {
+        type: 'string',
+        description: "A path on the app's server, starting with /.",
+      },
+      method: { type: 'string', enum: [...METHODS] },
+      headers: {
+        type: 'object',
+        description: 'Request headers; only Accept and Content-Type are sent.',
+      },
+      body: { type: 'string', description: 'The request body, base64.' },
+      id: {
+        type: 'string',
+        description: 'Continue a response an earlier call returned in parts.',
+      },
+      offset: { type: 'integer', minimum: 0 },
+    },
+    additionalProperties: false,
+  },
+  requires: ['app'],
+  ui: { visibility: ['app'] },
+  async run(args, { services, signal }) {
+    forget();
+    if (args.id !== undefined) {
+      const entry = held.get(args.id);
+      if (!entry)
+        throw new ToolError(
+          'invalid_arguments',
+          'That response is no longer held; request the path again',
+        );
+      return {
+        summary: `Part of ${entry.path}`,
+        data: part(entry.response, entry.bytes, args.offset ?? 0),
+      };
+    }
+    const path = checkedPath(args.path);
+    const method = args.method ?? 'GET';
+    if (!METHODS.has(method))
+      throw new ToolError('invalid_arguments', `Unsupported method ${method}`);
+    const headers = {};
+    for (const [name, value] of Object.entries(args.headers ?? {})) {
+      if (FORWARDED_REQUEST_HEADERS.includes(name.toLowerCase()))
+        headers[name] = String(value);
+    }
+    let answer;
+    try {
+      answer = await services.app.fetch(path, {
+        method,
+        headers,
+        ...(args.body !== undefined && method === 'POST'
+          ? { body: fromBase64(args.body) }
+          : {}),
+        signal,
+      });
+    } catch (error) {
+      if (signal?.aborted) throw error;
+      throw new ToolError('unavailable', "The app's server did not answer");
+    }
+    let bytes = new Uint8Array(await answer.arrayBuffer());
+    const type = answer.headers.get('content-type') || '';
+    let encoding = 'identity';
+    if (bytes.length >= COMPRESS_MIN_BYTES && !INCOMPRESSIBLE.test(type)) {
+      bytes = await gzip(bytes);
+      encoding = 'gzip';
+    }
+    const responseHeaders = {};
+    answer.headers.forEach((value, name) => {
+      if (!DROPPED_RESPONSE_HEADERS.has(name)) responseHeaders[name] = value;
+    });
+    const response = {
+      status: answer.status,
+      statusText: answer.statusText,
+      headers: responseHeaders,
+      encoding,
+      totalBytes: bytes.length,
+    };
+    if (bytes.length > PANEL_PART_BYTES) {
+      response.id = crypto.randomUUID();
+      held.set(response.id, {
+        path,
+        response,
+        bytes,
+        expires: Date.now() + HELD_MS,
+      });
+      heldBytes += bytes.length;
+    }
+    return {
+      summary: `${answer.status} ${method} ${path}`,
+      data: part(response, bytes, 0),
+    };
+  },
+});

src/tools/queries/panelRequest.test.mjs

@@ -0,0 +1,109 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { composeCatalog, coreTools } from '../index.js';
+import { PANEL_PART_BYTES } from './panelRequest.js';
+
+const fromBase64 = (text) => Buffer.from(text, 'base64');
+const gunzip = async (bytes) =>
+  new Uint8Array(
+    await new Response(
+      new Blob([bytes]).stream().pipeThrough(new DecompressionStream('gzip')),
+    ).arrayBuffer(),
+  );
+
+function catalogWith(handler) {
+  const requests = [];
+  const fetchImpl = async (path, init) => {
+    requests.push({ path, ...init });
+    return handler(path, init);
+  };
+  return {
+    requests,
+    catalog: composeCatalog({
+      tools: coreTools,
+      services: {
+        app: { baseUrl: 'http://localhost:4173/', fetch: fetchImpl },
+      },
+    }),
+  };
+}
+
+test('panel_request is for the panel only', () => {
+  const { catalog } = catalogWith(() => new Response('x'));
+  assert.deepEqual(catalog.get('panel_request').ui, { visibility: ['app'] });
+});
+
+test('a small response returns whole, compressed when that helps', async () => {
+  const text = 'body { color: red; }\n'.repeat(200);
+  const { catalog, requests } = catalogWith(
+    () =>
+      new Response(text, {
+        status: 200,
+        headers: { 'content-type': 'text/css', 'set-cookie': 'a=b' },
+      }),
+  );
+  const { data } = await catalog.call('panel_request', {
+    path: '/panel/assets/style.css',
+    headers: { Accept: 'text/css', Cookie: 'secret', 'X-Other': '1' },
+  });
+  assert.deepEqual(requests[0].headers, { Accept: 'text/css' });
+  assert.equal(data.status, 200);
+  assert.equal(data.encoding, 'gzip');
+  assert.equal(data.nextOffset, undefined);
+  assert.equal(data.headers['content-type'], 'text/css');
+  assert.equal(data.headers['set-cookie'], undefined);
+  const body = await gunzip(fromBase64(data.body));
+  assert.equal(new TextDecoder().decode(body), text);
+});
+
+test('a large response comes in parts that join to the original', async () => {
+  const bytes = new Uint8Array(PANEL_PART_BYTES * 2 + 10);
+  for (let index = 0; index < bytes.length; index++)
+    bytes[index] = (index * 7919) % 251;
+  const { catalog } = catalogWith(
+    () => new Response(bytes, { headers: { 'content-type': 'image/png' } }),
+  );
+  let { data } = await catalog.call('panel_request', { path: '/a.png' });
+  assert.equal(data.encoding, 'identity');
+  assert.equal(data.totalBytes, bytes.length);
+  const parts = [fromBase64(data.body)];
+  while (data.nextOffset !== undefined) {
+    ({ data } = await catalog.call('panel_request', {
+      id: data.id,
+      offset: data.nextOffset,
+    }));
+    parts.push(fromBase64(data.body));
+  }
+  assert.equal(parts.length, 3);
+  assert.deepEqual(new Uint8Array(Buffer.concat(parts)), bytes);
+});
+
+test('a request body and method pass through; settings and other sites do not', async () => {
+  const { catalog, requests } = catalogWith(
+    () => new Response('{}', { status: 201 }),
+  );
+  const { data } = await catalog.call('panel_request', {
+    path: '/api/openai/hud-summary',
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: Buffer.from('{"a":1}').toString('base64'),
+  });
+  assert.equal(data.status, 201);
+  assert.equal(new TextDecoder().decode(requests[0].body), '{"a":1}');
+  for (const path of [
+    '/api/setup/status',
+    '/api/setup',
+    '//evil.example/x',
+    'http://evil.example/',
+  ])
+    await assert.rejects(
+      catalog.call('panel_request', { path }),
+      (error) => error.code === 'invalid_arguments',
+      path,
+    );
+  await assert.rejects(
+    catalog.call('panel_request', { id: 'unknown' }),
+    (error) => error.code === 'invalid_arguments',
+  );
+  assert.equal(requests.length, 1);
+});