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/src/app.js

@@ -186,6 +186,47 @@ modules.load({
 
 app.use('/api', (req, res) => res.status(404).json({ message: 'Not found' }))
 
+// Installed modules' prebuilt client chunks, at /modules/<id>/ — same-origin, so
+// `script-src 'self'` admits them with no nonce and no inline script
+// (docs/website/MODULE_API.md §3.1). Three properties, each load-bearing:
+//
+//   • The static root is the directory the ENTRY sits in, never the module root.
+//     One express.static over a module root would publish its server source, its
+//     module.json and its schema fragment; the loader rejects an entry that would
+//     make those the same directory.
+//   • Behind the module's own state guard, so a failed module's chunk is 503 and
+//     a disabled one's is 404 — the same answers its API gives, for the same
+//     reason: the browser should not be running the client half of something the
+//     server half has stopped serving.
+//   • `fallthrough: false`, so a missing file is a 404 here rather than falling
+//     through to the SPA catch-all and answering a `<script src>` with the index
+//     shell, which the browser then rejects on its MIME type instead.
+//
+// Vite's library build emits an unhashed `entry.js`, so `no-cache` (revalidate,
+// not "do not store") is what stops an upgraded module serving yesterday's chunk
+// out of the disk cache.
+for (const chunk of modules.clientChunks()) {
+  app.use(
+    chunk.url,
+    chunk.guard,
+    express.static(chunk.dir, {
+      fallthrough: false,
+      setHeaders: (res) => {
+        res.set('Cache-Control', 'no-cache')
+        res.set('X-Content-Type-Options', 'nosniff')
+      },
+    }),
+  )
+}
+
+// Everything else under /modules is a 404, not the SPA shell. The namespace
+// belongs to installed modules' chunks — an unknown module id or a file a module
+// does not ship is a missing file, and answering a `<script src>` with an HTML
+// page turns that into a MIME-type refusal in the console with a 200 in the
+// network tab. It also keeps the namespace's boundary a fact of the app rather
+// than of whichever catch-all happens to be mounted after it.
+app.use('/modules', (req, res) => res.status(404).json({ message: 'Not found' }))
+
 // ── /.well-known ──────────────────────────────────────────────────────
 // Android App Links verification file at the web root (M9 follow-up). Mounted
 // before the SPA catch-all so it returns JSON, not the index shell. 404s unless

server/src/modules/loader.js

@@ -17,9 +17,11 @@
 // past its own try/catch — a bad module must cost the site its routes, never its
 // boot (§4.4).
 //
-// What is deliberately NOT here yet, each landing with the PR that first calls
-// it (§2.7): GET /api/v1/public/modules and the client chunk's static mount
-// (PRs 6-7).
+// PR 7 added the client half's server-side end: validating `client.entry` and
+// publishing where the chunk lives (`clientChunks()`), so app.js can serve it and
+// utils/htmlShell.js can inject its script tag. The loader resolves and validates;
+// it does not mount, because the chunk hangs off the ROOT app rather than a tier
+// router, and app.js is where core's own static mounts live.
 //
 // PR 3 added the fragment half of the schema story: this file VALIDATES a
 // fragment (statement by statement, at load time, before anything is mounted)
@@ -322,6 +324,58 @@ function ownedByCore(tierRouter, prefix) {
   )
 }
 
+// ── The client chunk ───────────────────────────────────────────────────────
+
+// A chunk filename, and the same character set utils/htmlShell.js will accept in
+// a script src. Two copies of the rule, deliberately: this one rejects the module
+// at load time, that one refuses to write the tag. A validator three files away
+// staying strict is not something an HTML attribute should depend on.
+const CHUNK_FILE = /^[A-Za-z0-9][A-Za-z0-9._-]*\.js$/
+
+/**
+ * Resolve and validate `client.entry` — where a module's prebuilt chunk lives on
+ * disk, and the URL it is served at (§3.1).
+ *
+ * The rule that matters most is the last one, and it is the one a reviewer would
+ * not think to ask for: the static mount is rooted at the DIRECTORY THE ENTRY IS
+ * IN, not at the module root. One `express.static` over a module root would
+ * publish its server source, its `module.json` and its schema fragment to the
+ * internet. So an entry sitting directly in the module root is rejected rather
+ * than quietly turning the whole module into a public directory.
+ *
+ * @returns {{dir: string, url: string, entryUrl: string}|null} null when the
+ *   module ships no client half — a server-only module is perfectly normal.
+ */
+function resolveClient(dir, id, manifest) {
+  // Absent `client` is a server-only module. Present but empty is not the same
+  // thing: it states a client half and delivers none, which would be a module
+  // whose pages never load and nothing anywhere saying why.
+  if (manifest.client === undefined) return null
+  const { entry } = manifest.client
+  if (typeof entry !== 'string' || !entry.trim()) fail('manifest', 'client.entry must be a path')
+
+  const file = path.resolve(dir, entry)
+  // Containment before anything else: `../../server/src/config` resolves to a
+  // real, readable directory, and every check below it would pass.
+  if (file !== dir && !file.startsWith(dir + path.sep)) {
+    fail('manifest', `client.entry "${entry}" escapes the module directory`)
+  }
+  if (!CHUNK_FILE.test(path.basename(file))) {
+    fail('manifest', `client.entry "${entry}" must name a .js file`)
+  }
+  const chunkDir = path.dirname(file)
+  if (chunkDir === dir) {
+    fail('manifest', `client.entry "${entry}" must be in a subdirectory — its directory is served`)
+  }
+  if (!fs.existsSync(file)) fail('manifest', `client.entry "${entry}" is missing`)
+
+  return {
+    dir: chunkDir,
+    url: `/modules/${id}`,
+    entryUrl: `/modules/${id}/${path.basename(file)}`,
+  }
+}
+
 function readManifest(dir, id, tierRouters) {
   const file = path.join(dir, 'module.json')
   const manifest = JSON.parse(fs.readFileSync(file, 'utf8'))
@@ -358,6 +412,15 @@ function readManifest(dir, id, tierRouters) {
     if (!registries.hasSlot(slot)) fail('extensions', `unknown extension slot "${slot}"`)
   }
 
+  if (manifest.client !== undefined) {
+    if (typeof manifest.client !== 'object' || manifest.client === null || Array.isArray(manifest.client)) {
+      fail('manifest', 'client must be an object')
+    }
+    for (const key of Object.keys(manifest.client)) {
+      if (key !== 'entry') fail('manifest', `unknown key "client.${key}" in module.json`)
+    }
+  }
+
   if (manifest.schema && !manifest.purge) {
     // A module that can create tables and cannot drop them leaves an operator
     // with orphaned data and no supported way to remove it.
@@ -434,6 +497,7 @@ function load(tierRouters) {
       tables: new Set(),
       called: new Set(),
       hooks: { onBoot: null, onShutdown: null },
+      client: null,
       ctx: null,
       state: 'installed',
       stage: null,
@@ -446,6 +510,7 @@ function load(tierRouters) {
     let stage = 'manifest'
     try {
       record.manifest = readManifest(dir, id, tierRouters)
+      record.client = resolveClient(dir, id, record.manifest)
       stage = 'schema'
       record.tables = tablesOf(dir, record.manifest)
       checkTableNames(id, record.tables)
@@ -522,17 +587,35 @@ function load(tierRouters) {
 function mount(record, tierRouters) {
   for (const tier of TIERS) {
     for (const [prefix, router] of record.routes[tier]) {
-      tierRouters[tier].use(prefix, (req, res, next) => {
-        if (record.state === 'startup_failed') {
-          return res.status(503).json({ message: 'Module unavailable' })
-        }
-        if (record.state === 'disabled') return res.status(404).json({ message: 'Not found' })
-        return next()
-      }, router)
+      tierRouters[tier].use(prefix, stateGuard(record), router)
     }
   }
 }
 
+/**
+ * The dispatch guard, as a middleware over the LIVE record.
+ *
+ * A closure over the record rather than over its state: everything mounts once,
+ * at boot, and the states that matter here are reached afterwards — the schema
+ * replay fails, `onBoot` throws, an admin disables the module. A guard that read
+ * the state at mount time would answer for the state a module was in before any
+ * of that happened.
+ *
+ * Used for a module's API routes and, since PR 7, for its client chunk: a module
+ * answering 503 on its API must not also be handing the browser the script that
+ * calls it, and one an admin has disabled should be as absent from the page as it
+ * is from the nav.
+ */
+function stateGuard(record) {
+  return (req, res, next) => {
+    if (record.state === 'startup_failed') {
+      return res.status(503).json({ message: 'Module unavailable' })
+    }
+    if (record.state === 'disabled') return res.status(404).json({ message: 'Not found' })
+    return next()
+  }
+}
+
 // ── State ──────────────────────────────────────────────────────────────────
 
 // The states a loaded record may hold, deliberately a hardcoded subset rather
@@ -657,7 +740,58 @@ function fragments() {
     .map((r) => ({ id: r.id, file: path.join(r.dir, r.manifest.schema) }))
 }
 
+/**
+ * Every module that ships a client chunk, with where to serve it from and the
+ * guard to serve it behind — in scan order.
+ *
+ * Listed regardless of state, because mounting happens once at boot and the
+ * guard is what answers for the state at request time (the same arrangement the
+ * API routes have). A module that failed VALIDATION never reaches here at all:
+ * `record.client` is only resolved once the manifest passed.
+ *
+ * `dir` is the directory the entry sits in, never the module root — see
+ * resolveClient. app.js does the mounting; this file does not know about the
+ * root app.
+ *
+ * @returns {{id: string, dir: string, url: string, entryUrl: string, guard: Function}[]}
+ */
+function clientChunks() {
+  assertLoaded('clientChunks')
+  return [...modules.values()]
+    .filter((r) => r.client)
+    .map((r) => ({ id: r.id, ...r.client, guard: stateGuard(r) }))
+}
+
+/**
+ * The script URLs the HTML shell should inject, in scan order.
+ *
+ * `started` only, and that is the difference between this and clientChunks():
+ * the mount is a standing offer answered by a guard, while the tag is a decision
+ * taken per page render, when the state is already known. A module whose `onBoot`
+ * failed keeps its URLs and answers 503 on them — loading its client half would
+ * render its pages against a backend that cannot serve them.
+ *
+ * @returns {string[]}
+ */
+function clientEntryUrls() {
+  assertLoaded('clientEntryUrls')
+  return [...modules.values()]
+    .filter((r) => r.client && r.state === 'started')
+    .map((r) => r.client.entryUrl)
+}
+
 /** Absolute path of the modules directory. */
 const dir = () => MODULES_DIR
 
-module.exports = { load, list, setState, fragments, bootable, shutdownHooks, isLoaded, dir }
+module.exports = {
+  load,
+  list,
+  setState,
+  fragments,
+  bootable,
+  shutdownHooks,
+  clientChunks,
+  clientEntryUrls,
+  isLoaded,
+  dir,
+}

server/src/utils/htmlShell.js

@@ -81,8 +81,9 @@ function absolutize(url) {
  * byte-identical property without a database.
  *
  * @param {string} html  the built index.html
- * @param {{logo?: string, favicon?: string, theme?: object|null}} [overrides]
- *   effective brand assets and theme; anything absent falls back to BRAND_* env
+ * @param {{logo?: string, favicon?: string, theme?: object|null, moduleEntries?: string[]}} [overrides]
+ *   effective brand assets and theme; anything absent falls back to BRAND_* env.
+ *   `moduleEntries` are the same-origin URLs of installed modules' client chunks.
  * @returns {string}
  */
 function render(html, overrides = {}) {
@@ -105,10 +106,43 @@ function render(html, overrides = {}) {
   ]
     .filter(Boolean)
     .join('\n    ')
-  return html
+  const scripts = moduleScriptTags(overrides.moduleEntries)
+  const withHead = html
     .replace(/<title>[\s\S]*?<\/title>/i, `<title>${title}</title>`)
     .replace(/(<meta\s+name="description"\s+content=")[\s\S]*?("\s*\/?>)/i, `$1${desc}$2`)
     .replace(/<\/head>/i, `    ${tags}\n  </head>`)
+  if (scripts.length === 0) return withHead
+  return withHead.replace(/<\/body>/i, `    ${scripts.join('\n    ')}\n  </body>`)
+}
+
+// Installed modules' prebuilt client chunks (docs/website/MODULE_API.md §3.1).
+//
+// `type="module"` with a `src`, never inline: `script-src 'self'` admits a
+// same-origin src with no nonce, and an inline tag would be blocked outright —
+// which is also why the shared dependencies ride on window.__rg rather than an
+// import map, since an import map has to be inline.
+//
+// **Injected before `</body>`, not into `</head>`, and the position is the
+// contract.** Module scripts are deferred, so they execute in document order
+// after core's own bundle — which is where `window.__rg` is published, and what
+// every one of a module's imports resolves against. Vite happens to hoist core's
+// entry script into `<head>` today, which would make a `</head>` injection work
+// too; that is a bundler's emit choice, and if it ever changed, every module in
+// the wild would break on its first import with nothing in this repo having been
+// edited. Last in the body is after core's script wherever core's script is.
+//
+// The path is built by the loader from the module id and the entry's basename,
+// both already validated, so nothing operator-supplied reaches the attribute.
+// It is re-checked here anyway: what may appear in an HTML attribute should be a
+// property of the code that writes the HTML, not of a validator two files away
+// staying strict.
+const MODULE_ENTRY_PATH = /^\/modules\/[a-z][a-z0-9-]{1,31}\/[A-Za-z0-9][A-Za-z0-9._-]*\.js$/
+
+function moduleScriptTags(entries) {
+  if (!Array.isArray(entries)) return []
+  return entries
+    .filter((src) => typeof src === 'string' && MODULE_ENTRY_PATH.test(src))
+    .map((src) => `<script type="module" src="${htmlEscape(src)}"></script>`)
 }
 
 // The admin theme as a :root block, or '' when this instance has never been
@@ -170,7 +204,26 @@ async function get() {
       // mean a failing query per page view.
       overrides = {}
     }
-    const html = render(template, overrides)
+    // The module list is in-memory and filesystem-derived, so unlike the brand
+    // read above it cannot fail on a DB fault and needs no fallback of its own.
+    // Required lazily for the same reason the settings model is: app.js requires
+    // this file, and the loader would otherwise be pulled into that chain.
+    let moduleEntries = []
+    try {
+      // eslint-disable-next-line global-require
+      moduleEntries = require('../modules/loader').clientEntryUrls()
+    } catch {
+      // The only reachable throw is §7.6's guard — the shell rendered before
+      // modules.load() ran, which app.js's ordering makes impossible and a test
+      // that renders in isolation makes possible. A page with no module scripts
+      // is the right answer either way; it is what a bare core serves.
+      moduleEntries = []
+    }
+    // Note for whoever builds the admin Modules screen: a state change after boot
+    // (an operator disabling a module) has to call invalidate(), exactly as a
+    // brand-asset write does. The TTL converges on its own within five minutes;
+    // the explicit call is what makes the toggle feel like it did something.
+    const html = render(template, { ...overrides, moduleEntries })
     // An invalidation that landed while this read was in flight means the value
     // we just read may already be stale. Serve it, but do not cache it.
     if (generation === startedAt) cached = { html, at: Date.now() }

server/test/htmlShell.test.js

@@ -227,3 +227,86 @@ test('an invalidation during a render is not overwritten by the stale result', a
   await inflight
   assert.match(await htmlShell.get(), /new\.png/, 'the pre-write value must not have been cached')
 })
+
+// ── Installed modules' client chunks (MODULE_API.md §3.1) ──────────────────
+
+// The built shell as Vite actually emits it: core's entry is a module script in
+// <head>, and the injection has to land AFTER it wherever it is.
+const BUILT_TEMPLATE = `<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <title>Vite App</title>
+    <meta name="description" content="placeholder" />
+    <script type="module" crossorigin src="/assets/index-abc123.js"></script>
+    <link rel="stylesheet" crossorigin href="/assets/index-abc123.css" />
+  </head>
+  <body><div id="root"></div></body>
+</html>`
+
+test('a module chunk is injected as a same-origin module script', () => {
+  const html = htmlShell.render(TEMPLATE, { moduleEntries: ['/modules/uo/entry.js'] })
+  assert.match(html, /<script type="module" src="\/modules\/uo\/entry\.js"><\/script>/)
+})
+
+test('the injection lands after core’s own bundle, not before it', () => {
+  // The property the whole client contract rests on: module scripts are deferred
+  // and execute in document order, so core's bundle must run first — it is what
+  // publishes window.__rg, and every import in the chunk resolves against it.
+  // Injecting into </head> would work today only because Vite hoists core's
+  // entry there; before </body> is after it wherever a bundler decides to put it.
+  const html = htmlShell.render(BUILT_TEMPLATE, { moduleEntries: ['/modules/uo/entry.js'] })
+  assert.ok(
+    html.indexOf('/assets/index-abc123.js') < html.indexOf('/modules/uo/entry.js'),
+    'the module chunk must come after core’s bundle',
+  )
+  assert.ok(html.indexOf('/modules/uo/entry.js') < html.indexOf('</body>'))
+  assert.ok(html.indexOf('</head>') < html.indexOf('/modules/uo/entry.js'))
+})
+
+test('several modules keep the order they were given', () => {
+  const html = htmlShell.render(TEMPLATE, {
+    moduleEntries: ['/modules/aaa/entry.js', '/modules/zzz/entry.js'],
+  })
+  assert.ok(html.indexOf('/modules/aaa/') < html.indexOf('/modules/zzz/'))
+})
+
+test('no installed modules leaves the shell byte-identical', () => {
+  // A bare core must serve exactly what it served before this PR — including
+  // when the list is absent rather than empty, which is what a render before
+  // modules.load() produces.
+  const baseline = legacyRenderIndexHtml(TEMPLATE)
+  assert.equal(htmlShell.render(TEMPLATE, { moduleEntries: [] }), baseline)
+  assert.equal(htmlShell.render(TEMPLATE, {}), baseline)
+})
+
+test('anything that is not a module chunk URL is refused, not escaped into the page', () => {
+  // The loader builds these from a validated id and a validated basename, so
+  // none of this is reachable today. It is enforced here anyway: what may appear
+  // in a script src should be a property of the code writing the HTML, not of a
+  // validator two files away staying strict.
+  const html = htmlShell.render(TEMPLATE, {
+    moduleEntries: [
+      'https://evil.example/entry.js',        // off-origin
+      '/modules/uo/../../etc/passwd',         // traversal
+      '/modules/UO/entry.js',                 // not a valid module id
+      '/modules/uo/entry.js"></script><script>alert(1)</script>', // attribute break-out
+      '/modules/uo/../secrets.js',
+      '/uploads/entry.js',                    // right shape, wrong root
+      42,
+      null,
+    ],
+  })
+  assert.ok(!html.includes('<script type="module" src='), html)
+  assert.equal(htmlShell.render(TEMPLATE, { moduleEntries: [] }), legacyRenderIndexHtml(TEMPLATE))
+})
+
+test('get() renders without module scripts when the loader has never scanned', async () => {
+  // db/seed.js's problem, one layer up: this file is required by app.js, and a
+  // render that reached the loader before modules.load() would throw §7.6's
+  // guard on a request path. A bare shell is the right answer.
+  settings.getShellBrand = async () => ({ logo: brand.logo, favicon: brand.favicon, theme: null })
+  htmlShell.init(TEMPLATE)
+  const html = await htmlShell.get()
+  assert.ok(!html.includes('/modules/'))
+})

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)
+})

server/test/moduleLoader.test.js

@@ -640,3 +640,105 @@ test('a module colliding with an already-registered name fails alone, unmounted'
   assert.equal(claims('/first'), true)
   assert.equal(claims('/second'), false)
 })
+
+// ── The client chunk (MODULE_API.md §3.1) ──────────────────────────────────
+
+/** A module shipping a prebuilt chunk at the conventional client/dist/entry.js. */
+function withChunk(id, { entry = 'client/dist/entry.js', write = true, body = 'export default 1' } = {}) {
+  const dir = writeModule(id, { manifest: { client: { entry } } })
+  if (write) {
+    const file = path.join(dir, entry)
+    fs.mkdirSync(path.dirname(file), { recursive: true })
+    fs.writeFileSync(file, body)
+  }
+  return dir
+}
+
+test('a module with a chunk publishes where to serve it from and its URL', () => {
+  const dir = withChunk('uo')
+  const loader = freshLoader(tmpRoot)
+  const [chunk] = loader.clientChunks()
+
+  assert.equal(chunk.id, 'uo')
+  assert.equal(chunk.url, '/modules/uo')
+  assert.equal(chunk.entryUrl, '/modules/uo/entry.js')
+  // The DIRECTORY THE ENTRY IS IN, never the module root: one express.static over
+  // a module root would publish its server source, its module.json and its schema
+  // fragment.
+  assert.equal(chunk.dir, path.join(dir, 'client', 'dist'))
+  assert.equal(typeof chunk.guard, 'function')
+})
+
+test('a server-only module contributes no chunk', () => {
+  writeModule('plain', { server: 'module.exports = () => {}' })
+  const loader = freshLoader(tmpRoot)
+  assert.deepEqual(loader.clientChunks(), [])
+  assert.deepEqual(loader.clientEntryUrls(), [])
+})
+
+test('an entry directly in the module root is refused — its directory is served', () => {
+  // The rule with the largest blast radius in this file. Accepting it would root
+  // the static mount at the module root and publish everything in it.
+  const dir = writeModule('uo', { manifest: { client: { entry: 'entry.js' } } })
+  fs.writeFileSync(path.join(dir, 'entry.js'), 'export default 1')
+  const loader = freshLoader(tmpRoot)
+  assert.equal(stateOf(loader, 'uo').state, 'startup_failed')
+  assert.match(stateOf(loader, 'uo').reason, /must be in a subdirectory/)
+  assert.deepEqual(loader.clientChunks(), [])
+})
+
+test('an entry that escapes the module directory is refused before anything else', () => {
+  // `../../server/src/config/csp.js` is a real, readable file, and every check
+  // after containment would have passed.
+  withChunk('uo', { entry: '../../server/src/config/csp.js', write: false })
+  const loader = freshLoader(tmpRoot)
+  assert.equal(stateOf(loader, 'uo').state, 'startup_failed')
+  assert.match(stateOf(loader, 'uo').reason, /escapes the module directory/)
+})
+
+test('an entry that is not a .js file, or is missing, is refused', () => {
+  withChunk('aaa', { entry: 'client/dist/entry.mjs' })
+  withChunk('bbb', { entry: 'client/dist/entry.js', write: false })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'aaa').reason, /must name a \.js file/)
+  assert.match(stateOf(loader, 'bbb').reason, /is missing/)
+})
+
+test('a malformed client key is a loud failure, not an ignored setting', () => {
+  writeModule('aaa', { manifest: { client: 'client/dist/entry.js' } })
+  writeModule('bbb', { manifest: { client: { entry: 'x/e.js', chunks: ['a.js'] } } })
+  writeModule('ccc', { manifest: { client: {} } })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'aaa').reason, /client must be an object/)
+  assert.match(stateOf(loader, 'bbb').reason, /unknown key "client\.chunks"/)
+  assert.match(stateOf(loader, 'ccc').reason, /client\.entry must be a path/)
+  for (const id of ['aaa', 'bbb', 'ccc']) assert.equal(stateOf(loader, id).stage, 'manifest')
+})
+
+test('only a STARTED module gets a script tag, though every one keeps its mount', () => {
+  // The mount is a standing offer answered by a guard; the tag is a decision
+  // taken per render, when the state is known. A module answering 503 on its API
+  // must not also be handing the browser the script that calls it.
+  withChunk('uo')
+  const loader = freshLoader(tmpRoot)
+  assert.deepEqual(loader.clientEntryUrls(), [], 'registered is not yet serving')
+
+  loader.setState('uo', 'started')
+  assert.deepEqual(loader.clientEntryUrls(), ['/modules/uo/entry.js'])
+
+  loader.setState('uo', 'startup_failed', { stage: 'boot', reason: 'nope' })
+  assert.deepEqual(loader.clientEntryUrls(), [])
+  assert.equal(loader.clientChunks().length, 1, 'the mount stays; the guard answers for it')
+
+  loader.setState('uo', 'disabled')
+  assert.deepEqual(loader.clientEntryUrls(), [])
+})
+
+test('the chunk accessors throw before load(), like every other one', () => {
+  process.env.MODULES_DIR = tmpRoot
+  delete require.cache[require.resolve('../src/modules/loader')]
+  // eslint-disable-next-line global-require
+  const loader = require('../src/modules/loader')
+  assert.throws(() => loader.clientChunks(), /modules\.clientChunks\(\) before modules\.load\(\)/)
+  assert.throws(() => loader.clientEntryUrls(), /modules\.clientEntryUrls\(\) before modules\.load\(\)/)
+})