feat(modules): the client registry, window.__rg and the chunk's script injection

Phase 2, PR 7 of docs/website/MODULE_SYSTEM.md 2.7 — the client half's
delivery. A module's prebuilt chunk is served, injected, handed core's React
and its UI kit, and its routes are rendered by App.jsx. The registry is empty
on a bare core, so nothing an operator can see changes.

Client:
  - modules/registry.js — registerRoutes/registerNav/registerFeatureProvider,
    with the URL namespace written by core, never by the module
  - modules/shared.js — window.__rg: React, react-dom/client, react-router-dom,
    react/jsx-runtime, the registry, the seven-member UI kit and the request
    primitive, frozen
  - App.jsx reads routesFor for all three areas; nav consumption is PR 8
  - main.jsx publishes the global, then mounts on DOMContentLoaded

Server:
  - the loader validates client.entry and publishes clientChunks() and
    clientEntryUrls(); an entry in the module root is rejected, because the
    directory it sits in is what gets served
  - app.js mounts each chunk at /modules/<id>/ behind the module's state guard
    with no-cache; anything else under /modules is a 404, not the SPA shell
  - htmlShell injects the tag before </body>, so core's bundle runs first
    wherever a bundler puts it

Found by loading a real chunk in a browser, and fixed here: core mounted before
any module chunk had evaluated, because document.readyState during a deferred
script is 'interactive', not 'loading'. Every test passed against that build.
The smoke is written down in MODULE_API.md 7.7.

933 server tests (+23), 123 client tests (+14). routes.manifest.json unchanged
at 230 routes; the OpenAPI spec regenerates byte-identical.

Co-Authored-By: Claude <noreply@anthropic.com>

server/test/moduleClientChunk.test.js

@@ -0,0 +1,180 @@
+// ── A module's client chunk, served by the real app ────────────────────────
+//
+// Phase 2, PR 7 of docs/website/MODULE_SYSTEM.md §2.7; the contract is
+// MODULE_API.md §3.1. moduleLoader.test.js proves the loader resolves and
+// validates the chunk; this file proves what the app does with the answer, and
+// it boots the REAL app.js to do it — because the three properties worth locking
+// are properties of the mount, not of the loader:
+//
+//   1. the module's own dist directory is published, and nothing above it;
+//   2. the chunk is served behind the module's state guard, so a failed or
+//      disabled module's client half is as absent as its API;
+//   3. a miss is a 404 and never the SPA shell, which a browser would reject on
+//      its MIME type after the request appeared to succeed.
+//
+// The modules directory is written and MODULES_DIR is set BEFORE app.js is
+// required, because the scan is synchronous and happens during that require.
+// Node's test runner gives each file its own process, so this cannot disturb
+// another test's view of the loader.
+
+process.env.DB_HOST = '127.0.0.1'
+process.env.DB_PORT = '59999'
+
+const fs = require('fs')
+const os = require('os')
+const path = require('path')
+
+const { test, before, after } = require('node:test')
+const assert = require('node:assert/strict')
+
+const CHUNK = 'export const hello = 1\n'
+
+const tmpRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'rg-module-chunk-'))
+const dist = path.join(tmpRoot, 'uo', 'client', 'dist')
+fs.mkdirSync(dist, { recursive: true })
+fs.writeFileSync(path.join(dist, 'entry.js'), CHUNK)
+fs.writeFileSync(path.join(dist, 'sidecar.js'), 'export const also = 2\n')
+// The two files a static mount rooted one level too high would publish.
+fs.writeFileSync(path.join(tmpRoot, 'uo', 'secrets.js'), 'const TOKEN = "leak"\n')
+fs.writeFileSync(
+  path.join(tmpRoot, 'uo', 'module.json'),
+  JSON.stringify({
+    id: 'uo',
+    name: 'Ultima Online',
+    version: '1.0.0',
+    coreApi: '^1.0.0',
+    client: { entry: 'client/dist/entry.js' },
+  }),
+)
+process.env.MODULES_DIR = tmpRoot
+
+/* eslint-disable global-require */
+const app = require('../src/app')
+const loader = require('../src/modules/loader')
+const db = require('../src/utils/db')
+const htmlShell = require('../src/utils/htmlShell')
+const settings = require('../src/model/settings/settings.model')
+/* eslint-enable global-require */
+
+let server
+let base
+
+before(async () => {
+  server = await new Promise((resolve) => {
+    const s = app.listen(0, '127.0.0.1', () => resolve(s))
+  })
+  base = `http://127.0.0.1:${server.address().port}`
+  // The state the module would be in after a clean boot. lifecycle.js does this
+  // against the database; here it is set directly, since what is under test is
+  // what the mount does with a state, not how the state was reached.
+  loader.setState('uo', 'started')
+})
+
+after(async () => {
+  server.closeAllConnections()
+  await new Promise((resolve) => server.close(resolve))
+  await db.close()
+  fs.rmSync(tmpRoot, { recursive: true, force: true })
+})
+
+test('the chunk is served at the URL the shell injects', async () => {
+  const [entryUrl] = loader.clientEntryUrls()
+  assert.equal(entryUrl, '/modules/uo/entry.js')
+
+  const res = await fetch(base + entryUrl)
+  assert.equal(res.status, 200)
+  assert.equal(await res.text(), CHUNK)
+  // A module chunk is JavaScript to the browser or it is nothing: a `<script
+  // type="module">` whose response is not a JS MIME type is refused outright.
+  assert.match(res.headers.get('content-type'), /javascript/)
+})
+
+test('a sibling file in the same dist directory is served too', async () => {
+  // Not incidental: Rollup can split a chunk, and the entry then imports its
+  // siblings by relative URL. Publishing only the named entry would break every
+  // module that is more than one file.
+  const res = await fetch(`${base}/modules/uo/sidecar.js`)
+  assert.equal(res.status, 200)
+})
+
+test('nothing above the dist directory is reachable', async () => {
+  // The failure this rule exists to prevent: server source, module.json and the
+  // schema fragment published to the internet by one over-broad static mount.
+  for (const p of ['/modules/uo/module.json', '/modules/uo/secrets.js', '/modules/uo/../module.json']) {
+    const res = await fetch(base + p)
+    assert.notEqual(res.status, 200, `${p} must not be served`)
+    assert.ok(!(await res.text()).includes('leak'))
+  }
+})
+
+test('the chunk revalidates rather than being cached to a stale copy', async () => {
+  // Vite's library build emits an unhashed entry.js, so an upgraded module would
+  // otherwise keep serving yesterday's chunk out of the browser's disk cache.
+  const res = await fetch(`${base}/modules/uo/entry.js`)
+  assert.equal(res.headers.get('cache-control'), 'no-cache')
+  assert.equal(res.headers.get('x-content-type-options'), 'nosniff')
+})
+
+test('a missing file is a 404, not the SPA shell', async () => {
+  const res = await fetch(`${base}/modules/uo/nope.js`)
+  assert.equal(res.status, 404)
+  assert.ok(!(await res.text()).includes('<div id="root">'))
+})
+
+test('an unknown module id is not served at all', async () => {
+  const res = await fetch(`${base}/modules/nope/entry.js`)
+  assert.notEqual(res.status, 200)
+})
+
+test('a failed module’s chunk is 503 and a disabled one’s is 404', async () => {
+  // The same answers the module's API routes give, and for the same reason: the
+  // browser must not be running the client half of something the server half has
+  // stopped serving.
+  loader.setState('uo', 'startup_failed', { stage: 'boot', reason: 'onBoot threw' })
+  let res = await fetch(`${base}/modules/uo/entry.js`)
+  assert.equal(res.status, 503)
+
+  loader.setState('uo', 'disabled')
+  res = await fetch(`${base}/modules/uo/entry.js`)
+  assert.equal(res.status, 404)
+
+  // And the guard reads the LIVE state — the mount happened once, at boot, long
+  // before any of these transitions.
+  loader.setState('uo', 'started')
+  res = await fetch(`${base}/modules/uo/entry.js`)
+  assert.equal(res.status, 200)
+})
+
+test('the module is published to clients while it is started, and only then', async () => {
+  // Ties the two surfaces together: /public/modules and the injected script tag
+  // answer the same question — what is serving — and they must never disagree.
+  const seen = async () => {
+    const res = await fetch(`${base}/api/v1/public/modules`)
+    return (await res.json()).modules.map((m) => m.id)
+  }
+  assert.deepEqual(await seen(), ['uo'])
+  assert.deepEqual(loader.clientEntryUrls(), ['/modules/uo/entry.js'])
+
+  loader.setState('uo', 'disabled')
+  assert.deepEqual(await seen(), [])
+  assert.deepEqual(loader.clientEntryUrls(), [])
+  loader.setState('uo', 'started')
+})
+
+test('the shell hands the browser the tag for the chunk the app serves', async () => {
+  // The one seam htmlShell.test.js cannot cover, because it renders against a
+  // literal list: that the shell asks the LOADER, and gets back a URL this same
+  // app answers 200 on. The two are wired through a lazy require inside a
+  // try/catch, which is exactly the shape that can silently return [] forever.
+  //
+  // The settings read is stubbed rather than left to fail: the pool points at a
+  // dead port, and its ten-second connect timeout would be paid here for a
+  // fallback the test does not care about.
+  settings.getShellBrand = async () => ({ logo: '', favicon: '', theme: null })
+  htmlShell.init('<!doctype html><html><head><title>t</title></head><body><div id="root"></div></body></html>')
+  const html = await htmlShell.get()
+
+  assert.match(html, /<script type="module" src="\/modules\/uo\/entry\.js"><\/script>/)
+  const res = await fetch(`${base}/modules/uo/entry.js`)
+  assert.equal(res.status, 200)
+})