feat(module): the bundle skeleton (phase 3, slice 0)

The first real module. It registers nothing, deliberately: what slice 0 proves
is the delivery path itself, end to end, before a single UO file moves into it.

Server half: module.json, an entry point that takes (ctx, api) and registers
nothing, a test suite built on a fake ctx, and scripts/checkImports.js -- the
MODULE_API.md §5.1 boundary check. Client half: the Vite library build, four
shims re-exporting react / react-dom/client / react-router-dom / jsx-runtime
from window.__rg, an entry that verifies each is identity-equal to core's copy,
and scripts/checkExternals.js. 29 server tests, 9 client tests, both new.

Verified against a real core: the module loads, mounts its zero routes, runs to
`started`, and is published by /api/v1/public/modules. Its chunk serves from
the entry's directory with `Cache-Control: no-cache` while the module's server
source, module.json and package.json all 404. In Chrome, under the enforced
`script-src 'self'`, the chunk evaluates and reports all four shared
dependencies OK, with zero CSP reports and no console errors.

Three findings, each of which had produced a green build that was wrong.

MODULE_API.md §3.6 shows `external` alongside the aliases and they do not
compose. Rollup asks `external` BEFORE Vite's alias resolver runs, so a
specifier in both is marked external and never aliased -- the chunk then ships
bare `import "react"`, which no browser can resolve without an import map, and
CSP forbids one. Built cleanly and emitted exactly that; checkExternals caught
it. So: alias only, `external` empty, and vite.config.js grows a resolution-time
guard that fails the build if a shared dependency resolves into node_modules.

That guard was wrong twice before it worked. Written against Rollup's `load`
hook it never ran -- `load` is first-wins and an earlier plugin had already
claimed the module -- so a deliberately-broken alias produced a 24 kB chunk with
react-router welded in, and a green build. And its forbidden-package list was
derived from the alias list "so the two cannot disagree", which meant deleting
an alias also deleted the guard against what that alias prevented. It states the
contract now, and a test asserts the aliases stay inside it.

checkImports failed on its own documentation the first time it ran: the comment
naming require("../../etc/passwd") as an example of what to catch, and index.js
explaining why the module must never require("express"). A boundary check that
cannot survive being described is one people stop writing comments around. It
strips comments and template literals with a character walk rather than a
regexp, because a URL in a string contains a comment opener and a comment
contains quotes -- and it has its own test suite, since a check never shown to
fail is a check nobody knows the state of.

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

client/src/shim/jsx-runtime.js

@@ -0,0 +1,14 @@
+// `react/jsx-runtime`, from core.
+//
+// Every .jsx file this module compiles becomes imports from `react/jsx-runtime`
+// under the automatic runtime, which is the default the tooling assumes. Those
+// have to resolve to CORE's React like every other import — a second jsx runtime
+// bound to a second React is the same one-React violation as bundling `react`
+// itself, only harder to see, because it shows up as a hook dispatcher error in
+// a component that looks fine.
+
+const jsxRuntime = window.__rg.jsxRuntime
+
+export const { jsx, jsxs, jsxDEV, Fragment } = jsxRuntime
+
+export default jsxRuntime.default ?? jsxRuntime

client/src/shim/react-dom.js

@@ -0,0 +1,12 @@
+// `react-dom/client`, from core.
+//
+// A module never calls `createRoot` — core owns the root and the module renders
+// inside it. This exists because a transitive import can still reach for
+// react-dom, and one that resolved to a bundled copy would put a second
+// renderer in the page.
+
+const reactDom = window.__rg.reactDom
+
+export default reactDom.default ?? reactDom
+
+export const { createRoot, hydrateRoot, flushSync, createPortal } = reactDom

client/src/shim/react-router-dom.js

@@ -0,0 +1,30 @@
+// `react-router-dom`, from core.
+//
+// The sharpest of the four, because router state is not just a library — it is
+// one live navigation context. A module with its own copy would get a router
+// whose `useParams` returns nothing and whose `<Link>` navigates the browser
+// instead of the SPA, on a page that otherwise renders perfectly.
+
+const router = window.__rg.router
+
+export default router.default ?? router
+
+export const {
+  BrowserRouter,
+  Link,
+  NavLink,
+  Navigate,
+  Outlet,
+  Route,
+  Routes,
+  createSearchParams,
+  generatePath,
+  matchPath,
+  useLocation,
+  useMatch,
+  useNavigate,
+  useOutletContext,
+  useParams,
+  useResolvedPath,
+  useSearchParams,
+} = router

client/src/shim/react.js

@@ -0,0 +1,48 @@
+// The shared React, taken from core rather than bundled.
+//
+// Why a shim file exists at all (MODULE_API.md §3.6, and the spike proved it the
+// hard way): Rollup's `external` alone emits a bare `import 'react'` into the
+// chunk, which the browser cannot resolve without an import map — and an import
+// map has to be an inline `<script type="importmap">`, which core's
+// `script-src 'self'` forbids. `output.globals` does not help either; it is
+// iife/umd only, and this is an ES module. So each shared dependency is aliased
+// to a two-line module that re-exports from the global core published before any
+// module chunk evaluated.
+//
+// The named re-exports are not decoration: `import { useState } from 'react'`
+// compiles to a named import, and a module with only a default export would fail
+// at link time in the browser with a message about the binding, not about this.
+
+const react = window.__rg.react
+
+export default react.default ?? react
+
+export const {
+  Children,
+  Component,
+  Fragment,
+  StrictMode,
+  Suspense,
+  cloneElement,
+  createContext,
+  createElement,
+  forwardRef,
+  isValidElement,
+  lazy,
+  memo,
+  useCallback,
+  useContext,
+  useDebugValue,
+  useDeferredValue,
+  useEffect,
+  useId,
+  useImperativeHandle,
+  useInsertionEffect,
+  useLayoutEffect,
+  useMemo,
+  useReducer,
+  useRef,
+  useState,
+  useSyncExternalStore,
+  useTransition,
+} = react