test: guard ES5 runtime APIs and type-check consumers in CI

Follow-up to the ES5 syntax fix, closing the gaps that investigation left.

An ES5-only runtime sandbox. The acorn check catches syntax, but syntax is
only half the contract: preset-env lowers syntax and never polyfills library
calls, so one `Array.prototype.includes` in the parser source compiles
cleanly, passes every test on modern Node, and throws on the browsers es5.js
exists for. The new test runs both legacy bundles in a vm context with the
post-ES5.1 globals, statics and prototype methods deleted, and asserts
bundled.js additionally installs the polyfills its README entry promises.
Includes a test that the sandbox really strips, so it cannot quietly pass
against a modern global.

A consumer type-check across every module resolution mode, run in CI against
the packed tarball. attw already checks that types *resolve* per condition;
it compiles nothing, so it cannot catch a declaration that resolves correctly
and then misdescribes the runtime. Negative cases are asserted too — the maps
must stay non-importable as named exports, which is the line index.d.mts
draws deliberately and only a failing compile can hold.

Also documents two findings that were investigated and deliberately left
alone: the bundled.js size increase is the core-js 2 -> 3 upgrade rather than
waste, and `useBuiltIns: 'usage'` would shrink it by breaking the documented
"all needed polyfills" contract; and the src/*.js ESM-in-CJS wart (publint
warnings, Yarn PnP, Node < 20.19) is longstanding and identical on 2.14.1,
with the nested-package.json fix blocked on @babel/register.

Verified by breaking each guard in turn: an ES6 API call injected into es5.js
fails the sandbox test, and an index.d.mts with its `parse` export removed
fails all three ESM resolution modes while the CJS modes correctly still pass.

test/types/check.mjs

@@ -0,0 +1,135 @@
+/**
+ * Type-checks a real consumer against the *packed* package under every module
+ * resolution mode TypeScript offers.
+ *
+ *   node test/types/check.mjs <path-to-bowser-x.y.z.tgz>
+ *
+ * `attw` already runs in CI, but it answers a narrower question: whether the
+ * types *resolve* to the right file for each condition. It does not compile
+ * anything, so it cannot catch a declaration that resolves fine and then fails
+ * to describe the runtime — a missing member, a wrong signature, or a named
+ * export declared in `index.d.mts` that `bowser.mjs` does not actually have.
+ *
+ * Both directions are asserted. The negative cases matter as much as the
+ * positive ones: `index.d.mts` deliberately omits `BROWSER_MAP` and friends as
+ * named exports because importing them that way throws at runtime, and only a
+ * compile that is expected to *fail* can hold that line.
+ *
+ * Run against the tarball rather than the repo so the exports map, the
+ * `types`/`typesVersions` fields and the published file list are all exercised
+ * exactly as a consumer sees them.
+ */
+import cp from 'node:child_process';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const repoRoot = path.join(here, '..', '..');
+const tsc = path.join(repoRoot, 'node_modules', '.bin', 'tsc');
+
+const tarball = process.argv[2];
+if (!tarball || !fs.existsSync(tarball)) {
+  console.error('usage: node test/types/check.mjs <path-to-tarball.tgz>');
+  process.exit(1);
+}
+
+/** Each mode a real consumer can be configured with. */
+const MODES = [
+  { name: 'node10 (CJS)', moduleResolution: 'node10', module: 'commonjs', type: 'commonjs', fixture: 'consumer-cjs.ts' },
+  { name: 'node16 (CJS)', moduleResolution: 'node16', module: 'node16', type: 'commonjs', fixture: 'consumer-cjs.ts' },
+  { name: 'node16 (ESM)', moduleResolution: 'node16', module: 'node16', type: 'module', fixture: 'consumer-esm.ts' },
+  { name: 'nodenext (ESM)', moduleResolution: 'nodenext', module: 'nodenext', type: 'module', fixture: 'consumer-esm.ts' },
+  { name: 'bundler', moduleResolution: 'bundler', module: 'esnext', type: 'module', fixture: 'consumer-esm.ts' },
+];
+
+/**
+ * Imports that must NOT compile, because the runtime does not provide them.
+ * Keeps `index.d.mts` honest — if any of these starts compiling, the types are
+ * promising something `bowser.mjs` will not deliver.
+ */
+const MUST_NOT_COMPILE = [
+  ['BROWSER_MAP is not a named export', 'import { BROWSER_MAP } from "bowser"; export default BROWSER_MAP;'],
+  ['OS_MAP is not a named export', 'import { OS_MAP } from "bowser"; export default OS_MAP;'],
+  ['ENGINE_MAP is not a named export', 'import { ENGINE_MAP } from "bowser"; export default ENGINE_MAP;'],
+  ['PLATFORMS_MAP is not a named export', 'import { PLATFORMS_MAP } from "bowser"; export default PLATFORMS_MAP;'],
+  ['Parser is a type, not a value', 'import { Parser } from "bowser"; export default new Parser("x");'],
+];
+
+const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'bowser-types-'));
+const modules = path.join(tmp, 'node_modules');
+fs.mkdirSync(modules, { recursive: true });
+cp.execFileSync('tar', ['xzf', path.resolve(tarball), '-C', modules]);
+fs.renameSync(path.join(modules, 'package'), path.join(modules, 'bowser'));
+
+/** Runs tsc over a single file in a project configured for `mode`. */
+function typeCheck(mode, fileName, source) {
+  // Nested one level under `tmp`, so resolution walks up into tmp/node_modules
+  // the way a real consumer's does. `paths` would short-circuit the exports map.
+  const dir = path.join(tmp, `case-${Math.abs(hash(mode.name + fileName))}`);
+  fs.mkdirSync(dir, { recursive: true });
+  fs.writeFileSync(path.join(dir, 'app.ts'), source);
+  fs.writeFileSync(path.join(dir, 'package.json'), JSON.stringify({
+    name: 'consumer', version: '1.0.0', private: true, type: mode.type,
+  }));
+  fs.writeFileSync(path.join(dir, 'tsconfig.json'), JSON.stringify({
+    compilerOptions: {
+      strict: true,
+      noEmit: true,
+      // Do not skip: a broken .d.ts in the package itself must fail the check.
+      skipLibCheck: false,
+      target: 'es2020',
+      module: mode.module,
+      moduleResolution: mode.moduleResolution,
+      esModuleInterop: true,
+      resolveJsonModule: true,
+      types: [],
+    },
+    files: ['app.ts'],
+  }));
+  const result = cp.spawnSync(tsc, ['-p', 'tsconfig.json'], { cwd: dir, encoding: 'utf8' });
+  return { ok: result.status === 0, output: `${result.stdout || ''}${result.stderr || ''}`.trim() };
+}
+
+function hash(s) {
+  let h = 0;
+  for (let i = 0; i < s.length; i += 1) { h = ((h << 5) - h + s.charCodeAt(i)) | 0; }
+  return h;
+}
+
+let failures = 0;
+console.log(`Type-checking consumers against ${path.basename(tarball)}\n`);
+
+for (const mode of MODES) {
+  const source = fs.readFileSync(path.join(here, 'fixtures', mode.fixture), 'utf8');
+  const { ok, output } = typeCheck(mode, mode.fixture, source);
+  if (ok) {
+    console.log(`  ok    ${mode.name.padEnd(16)} ${mode.fixture}`);
+  } else {
+    failures += 1;
+    console.log(`  FAIL  ${mode.name.padEnd(16)} ${mode.fixture}\n${output.replace(/^/gm, '          ')}`);
+  }
+}
+
+console.log('');
+// Only needs one ESM-shaped mode; the .d.mts is what is under test.
+const negativeMode = MODES.find((m) => m.name === 'node16 (ESM)');
+for (const [label, source] of MUST_NOT_COMPILE) {
+  const { ok } = typeCheck(negativeMode, `negative-${label}`, source);
+  if (ok) {
+    failures += 1;
+    console.log(`  FAIL  types accept something the runtime rejects: ${label}`);
+  } else {
+    console.log(`  ok    rejected: ${label}`);
+  }
+}
+
+try { fs.rmSync(tmp, { recursive: true, force: true }); } catch { /* best effort */ }
+
+console.log('');
+if (failures) {
+  console.error(`${failures} type check(s) failed`);
+  process.exit(1);
+}
+console.log(`all ${MODES.length + MUST_NOT_COMPILE.length} type checks passed`);

test/types/fixtures/consumer-cjs.ts

@@ -0,0 +1,15 @@
+// A CommonJS consumer: default import via esModuleInterop, types reached
+// through the `export =` namespace. This is what `moduleResolution: node10`
+// and `node16` (from CJS) consumers write.
+import Bowser from 'bowser';
+
+const UA = 'Mozilla/5.0 (Macintosh) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36';
+
+const result: Bowser.Parser.ParsedResult = Bowser.parse(UA);
+const parser: Bowser.Parser.Parser = Bowser.getParser(UA);
+const name: string | undefined = result.browser.name;
+const satisfies: boolean | undefined = parser.satisfies({ chrome: '>100' });
+const hints: Bowser.ClientHints = { mobile: false };
+const maps: Record<string, string> = Bowser.BROWSER_MAP;
+
+export { name, satisfies, hints, maps };

test/types/fixtures/consumer-esm.ts

@@ -0,0 +1,17 @@
+// An ES module consumer: default plus named imports, types imported as types.
+// This is `moduleResolution: node16` (from ESM), `nodenext` and `bundler`.
+import Bowser, { parse, getParser } from 'bowser';
+import type { ParsedResult, Parser, ClientHints, checkTree } from 'bowser';
+
+const UA = 'Mozilla/5.0 (Macintosh) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36';
+
+const result: ParsedResult = parse(UA);
+const parser: Parser = getParser(UA);
+const tree: checkTree = { chrome: '>100' };
+const satisfies: boolean | undefined = parser.satisfies(tree);
+const hints: ClientHints = { mobile: false };
+// BROWSER_MAP is deliberately not a named export of bowser.mjs — it only
+// exists as a static on the class. Reaching it any other way must not compile.
+const maps: Record<string, string> = Bowser.BROWSER_MAP;
+
+export { result, satisfies, hints, maps };