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>

server/test/checkImports.test.js

@@ -0,0 +1,136 @@
+// The boundary check, checked.
+//
+// `scripts/checkImports.js` is the acceptance test for the whole module contract
+// (MODULE_API.md §5.1), and a check that has never been shown to fail is a check
+// nobody knows the state of. These point it at fixtures that break each rule and
+// assert it says so — and at prose that merely *describes* breaking them, which
+// is what it got wrong the first time it was run.
+//
+// **Every fixture is a template literal, and that is load-bearing.** The scanner
+// reads the files in this directory too, so an ordinary quoted string holding
+// `require('../../x')` would make this file fail the very check it is testing.
+// Templates are blanked by the stripper for exactly this class of text: source
+// being composed as data is not source being imported.
+
+const test = require('node:test')
+const assert = require('node:assert')
+const fs = require('node:fs')
+const os = require('node:os')
+const path = require('node:path')
+
+const { scan, stripCommentsAndTemplates, SERVER_ROOT, MODULE_ROOT } = require('../scripts/checkImports')
+
+/** Write `files` into a throwaway module tree and scan it. */
+function scanFixture(files, { dev = new Set() } = {}) {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), 'module-uo-'))
+  const src = path.join(root, 'server')
+  for (const [name, source] of Object.entries(files)) {
+    const file = path.join(src, name)
+    fs.mkdirSync(path.dirname(file), { recursive: true })
+    fs.writeFileSync(file, source)
+  }
+  try {
+    return scan(src, root, { shipped: (f) => !f.startsWith(path.join(src, 'test') + path.sep), dev })
+  } finally {
+    fs.rmSync(root, { recursive: true, force: true })
+  }
+}
+
+test('the real server half is clean', () => {
+  assert.deepStrictEqual(scan(SERVER_ROOT, MODULE_ROOT), [])
+})
+
+test('catches a relative path that escapes the module root', () => {
+  const found = scanFixture({ 'a.js': `require('../../server/src/utils/db')` })
+  assert.strictEqual(found.length, 1)
+  assert.strictEqual(found[0].why, 'escapes the module root')
+})
+
+test('allows a relative path that stays inside it, however deep', () => {
+  assert.deepStrictEqual(
+    scanFixture({ 'deep/nested/a.js': `require('../../../module.json')` }),
+    [],
+  )
+})
+
+test('catches an absolute path', () => {
+  const found = scanFixture({ 'a.js': `require('/etc/passwd')` })
+  assert.strictEqual(found[0].why, 'absolute path')
+})
+
+test('catches a bare specifier in shipped code, even a devDependency', () => {
+  // The rule that makes the boundary real: express arrives on ctx. A shipped
+  // file requiring it would fail on a real install, because a module lives
+  // outside core's server/ and never reaches core's node_modules.
+  const found = scanFixture({ 'a.js': `const express = require('express')` }, { dev: new Set(['express']) })
+  assert.strictEqual(found.length, 1)
+  assert.match(found[0].why, /should this come from ctx/)
+})
+
+test('allows a devDependency in test code, which never runs inside core', () => {
+  assert.deepStrictEqual(
+    scanFixture({ 'test/a.js': `const express = require('express')` }, { dev: new Set(['express']) }),
+    [],
+  )
+})
+
+test('allows node builtins anywhere, with or without the node: prefix', () => {
+  assert.deepStrictEqual(
+    scanFixture({ 'a.js': `require('path'); require('node:fs'); import crypto from 'node:crypto'` }),
+    [],
+  )
+})
+
+test('catches ESM and dynamic forms, not only require()', () => {
+  const found = scanFixture({
+    'a.js': [`import db from '../../core/db.js'`, `const x = await import('../../core/other.js')`].join('\n'),
+  })
+  assert.strictEqual(found.length, 2)
+})
+
+test('ignores a violation that is only DESCRIBED in a comment', () => {
+  // The first run of this check failed on its own documentation, and on
+  // index.js's comment explaining why the module must never require('express').
+  // Prose about the rule must not trip the rule.
+  assert.deepStrictEqual(
+    scanFixture({
+      'a.js': [
+        `// Never write require("../../server/src/utils/db") - it escapes the module root.`,
+        `/* Nor import express from "express": core hands it over on ctx. */`,
+        `const path = require('path')`,
+      ].join('\n'),
+    }),
+    [],
+  )
+})
+
+test('ignores a specifier-shaped string inside a template literal', () => {
+  assert.deepStrictEqual(
+    scanFixture({ 'a.js': ['const sql = ', '`SELECT 1 -- require("../../x")`'].join('') }),
+    [],
+  )
+})
+
+test('a comment opener inside a string does not swallow the rest of the file', () => {
+  // The reason this is a character walk and not a regexp: a URL in a string
+  // contains `//`, and treating that as a comment would blank everything after
+  // it — turning the check into one that silently passes.
+  const found = scanFixture({
+    'a.js': [`const url = 'https://example.com/x'`, `require('../../escaped')`].join('\n'),
+  })
+  assert.strictEqual(found.length, 1, 'the specifier after a URL string was missed')
+})
+
+test('a quote inside a comment does not swallow the rest of the file', () => {
+  const found = scanFixture({
+    'a.js': [`// don't do this`, `require('../../escaped')`].join('\n'),
+  })
+  assert.strictEqual(found.length, 1)
+})
+
+test('stripping preserves line numbers', () => {
+  // Blanked rather than removed, so anything that later reports a line still
+  // reports the right one.
+  const src = ['/* a', 'b', 'c */', `require("x")`, ''].join('\n')
+  assert.strictEqual(stripCommentsAndTemplates(src).split('\n').length, src.split('\n').length)
+})