diff --git a/jest.config.js b/jest.config.js
index dbf98bf..f8e34a7 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -3,6 +3,7 @@ module.exports = {
     preset: 'ts-jest',
     testEnvironment: 'node',
     testMatch: ['**/tests/unit/**/*.test.ts', '**/tests/integration/**/*.test.ts'],
+    setupFiles: ['<rootDir>/tests/setup.ts'],
     transform: {
         '^.+\\.tsx?$': ['ts-jest', {
             tsconfig: {
diff --git a/rollup.config.mjs b/rollup.config.mjs
index 1e73602..a55e785 100644
--- a/rollup.config.mjs
+++ b/rollup.config.mjs
@@ -30,7 +30,15 @@ if (target === 'node') {
         },
         {
             file: 'dist/esm/index.mjs',
-            format: 'es'
+            format: 'es',
+            // The source loads several modules lazily via require(): the crypto
+            // fallback, fs/path for key persistence, the optional native addon,
+            // and jose. `require` does not exist in ES module scope, so without
+            // this shim an ESM consumer crashes with "require is not defined"
+            // the moment one of those paths runs. Node-only output, so
+            // node:module is safe here.
+            banner: "import { createRequire as __nomyoCreateRequire } from 'node:module';\n"
+                + 'const require = __nomyoCreateRequire(import.meta.url);'
         }
     ];
     config.external = ['crypto', 'https', 'fs', 'path'];
diff --git a/src/browser.ts b/src/browser.ts
index a79884c..dec271c 100644
--- a/src/browser.ts
+++ b/src/browser.ts
@@ -1,6 +1,18 @@
 /**
- * Browser-specific entry point
- * Ensures browser-specific implementations are used
+ * Browser-specific entry point.
+ *
+ * Registers the browser platform implementations before anything can ask for
+ * them, so the bundled build never needs a runtime path lookup. Wiring them in
+ * here also keeps the Node.js implementations — and their `https`/`fs` imports
+ * and the optional native addon — out of the browser bundle entirely.
  */
 
+import { registerSecureMemory } from './core/memory/secure';
+import { registerHttpClient } from './core/http/client';
+import { BrowserSecureMemory } from './core/memory/browser';
+import { BrowserHttpClient } from './core/http/browser';
+
+registerSecureMemory(() => new BrowserSecureMemory());
+registerHttpClient(() => new BrowserHttpClient());
+
 export * from './index';
diff --git a/src/core/http/client.ts b/src/core/http/client.ts
index f2ad6c4..1f8c076 100644
--- a/src/core/http/client.ts
+++ b/src/core/http/client.ts
@@ -20,17 +20,30 @@ export interface HttpClient {
     get(url: string, options?: Omit<HttpRequestOptions, 'body'>): Promise<HttpResponse>;
 }
 
+export type HttpClientFactory = () => HttpClient;
+
+let httpClientFactory: HttpClientFactory | null = null;
+
 /**
- * Create an HTTP client for the current platform
+ * Register the platform's HttpClient implementation.
+ *
+ * Called by the entry points (src/node.ts, src/browser.ts) at load time — see
+ * registerSecureMemory for why a runtime require cannot survive bundling.
+ */
+export function registerHttpClient(factory: HttpClientFactory): void {
+    httpClientFactory = factory;
+}
+
+/**
+ * Create an HTTP client for the current platform.
  */
 export function createHttpClient(): HttpClient {
-    if (typeof window !== 'undefined') {
-        // Browser environment
-        const BrowserHttpClient = require('./browser').BrowserHttpClient;
-        return new BrowserHttpClient();
-    } else {
-        // Node.js environment
-        const NodeHttpClient = require('./node').NodeHttpClient;
-        return new NodeHttpClient();
+    if (httpClientFactory === null) {
+        throw new Error(
+            'No HttpClient implementation registered. Import the package entry ' +
+            "point ('nomyo-js', or src/node.ts / src/browser.ts) rather than " +
+            'deep-importing core modules.'
+        );
     }
+    return httpClientFactory();
 }
diff --git a/src/core/memory/secure.ts b/src/core/memory/secure.ts
index 458c3d0..ea278f1 100644
--- a/src/core/memory/secure.ts
+++ b/src/core/memory/secure.ts
@@ -144,17 +144,32 @@ export class SecureByteContext {
     }
 }
 
+export type SecureMemoryFactory = () => SecureMemory;
+
+let secureMemoryFactory: SecureMemoryFactory | null = null;
+
 /**
- * Create a secure memory implementation for the current platform
+ * Register the platform's SecureMemory implementation.
+ *
+ * The entry points (src/node.ts, src/browser.ts) call this at load time. That
+ * matters for the bundled builds: rollup flattens every module into one file,
+ * so requiring the platform module by relative path at runtime would point at a
+ * path that no longer exists, and throw the moment platform code was needed.
+ */
+export function registerSecureMemory(factory: SecureMemoryFactory): void {
+    secureMemoryFactory = factory;
+}
+
+/**
+ * Create a secure memory implementation for the current platform.
  */
 export function createSecureMemory(): SecureMemory {
-    if (typeof window !== 'undefined') {
-        // Browser environment
-        const BrowserSecureMemory = require('./browser').BrowserSecureMemory;
-        return new BrowserSecureMemory();
-    } else {
-        // Node.js environment
-        const NodeSecureMemory = require('./node').NodeSecureMemory;
-        return new NodeSecureMemory();
+    if (secureMemoryFactory === null) {
+        throw new Error(
+            'No SecureMemory implementation registered. Import the package entry ' +
+            "point ('nomyo-js', or src/node.ts / src/browser.ts) rather than " +
+            'deep-importing core modules.'
+        );
     }
+    return secureMemoryFactory();
 }
diff --git a/src/node.ts b/src/node.ts
index e907955..5b9fe6d 100644
--- a/src/node.ts
+++ b/src/node.ts
@@ -1,6 +1,18 @@
 /**
- * Node.js-specific entry point
- * Ensures Node.js-specific implementations are used
+ * Node.js-specific entry point.
+ *
+ * Registers the Node.js platform implementations before anything can ask for
+ * them. This is what makes the bundled build work: rollup flattens all modules
+ * into a single file, so the platform layer cannot be discovered at runtime by
+ * relative path — it has to be wired in here, statically.
  */
 
+import { registerSecureMemory } from './core/memory/secure';
+import { registerHttpClient } from './core/http/client';
+import { NodeSecureMemory } from './core/memory/node';
+import { NodeHttpClient } from './core/http/node';
+
+registerSecureMemory(() => new NodeSecureMemory());
+registerHttpClient(() => new NodeHttpClient());
+
 export * from './index';
diff --git a/tests/integration/bundle.test.ts b/tests/integration/bundle.test.ts
new file mode 100644
index 0000000..ee16170
--- /dev/null
+++ b/tests/integration/bundle.test.ts
@@ -0,0 +1,164 @@
+/**
+ * Smoke tests for the BUILT bundles in dist/.
+ *
+ * Every other suite runs against src/ through ts-jest, where the platform
+ * modules resolve as ordinary relative paths. That masked a bug in which the
+ * published package loaded fine but threw "Cannot find module './node'" as soon
+ * as anything touched the platform layer — rollup flattens the modules, so the
+ * runtime require had nothing to resolve. The client could not be constructed
+ * at all from the npm package.
+ *
+ * These tests exercise the artefact that actually ships. Run `npm run build`
+ * first; they skip themselves if dist/ is absent.
+ */
+
+import * as fs from 'fs';
+import * as path from 'path';
+import { spawnSync } from 'child_process';
+
+const DIST = path.join(__dirname, '..', '..', 'dist');
+const NODE_CJS = path.join(DIST, 'node', 'index.js');
+const BROWSER_CJS = path.join(DIST, 'browser', 'index.cjs');
+const ESM_ENTRY = path.join(DIST, 'esm', 'index.mjs');
+
+const built = fs.existsSync(NODE_CJS);
+const describeIfBuilt = built ? describe : describe.skip;
+
+if (!built) {
+    // eslint-disable-next-line no-console
+    console.warn('dist/ not found — run `npm run build` to exercise the bundle smoke tests');
+}
+
+interface NomyoModule {
+    SecureChatCompletion: new (config?: object) => { dispose(): void };
+    SecureCompletionClient: new (config: object) => { dispose(): void };
+    getMemoryProtectionInfo: () => { method: string; canLock: boolean };
+    AttestationPolicy: new (options?: object) => { enforce: boolean };
+    SecurityError: new (message: string) => Error;
+}
+
+describeIfBuilt('built Node bundle', () => {
+    // eslint-disable-next-line @typescript-eslint/no-var-requires
+    const nomyo = require(NODE_CJS) as NomyoModule;
+
+    test('exposes the public API', () => {
+        expect(typeof nomyo.SecureChatCompletion).toBe('function');
+        expect(typeof nomyo.SecureCompletionClient).toBe('function');
+        expect(typeof nomyo.getMemoryProtectionInfo).toBe('function');
+        expect(typeof nomyo.AttestationPolicy).toBe('function');
+    });
+
+    test('constructs a client — the platform layer resolves', () => {
+        // This is the exact call that threw "Cannot find module './node'"
+        const client = new nomyo.SecureChatCompletion({});
+        expect(client).toBeTruthy();
+        client.dispose();
+    });
+
+    test('constructs the low-level client too', () => {
+        const client = new nomyo.SecureCompletionClient({
+            routerUrl: 'https://router.test',
+            keyRotationInterval: 0,
+        });
+        expect(client).toBeTruthy();
+        client.dispose();
+    });
+
+    test('reaches the real secure-memory implementation', () => {
+        const info = nomyo.getMemoryProtectionInfo();
+        expect(['mlock', 'zero-only', 'none']).toContain(info.method);
+        expect(typeof info.canLock).toBe('boolean');
+    });
+
+    test('carries no unresolved runtime requires', () => {
+        const source = fs.readFileSync(NODE_CJS, 'utf-8');
+        // './node' / './browser' only ever resolved pre-bundling
+        expect(source).not.toMatch(/require\(['"]\.\/node['"]\)/);
+        expect(source).not.toMatch(/require\(['"]\.\/browser['"]\)/);
+    });
+
+    test('attestation policy survives bundling', () => {
+        const policy = new nomyo.AttestationPolicy({ enforce: true });
+        expect(policy.enforce).toBe(true);
+    });
+});
+
+describeIfBuilt('built browser bundle', () => {
+    // eslint-disable-next-line @typescript-eslint/no-var-requires
+    const nomyo = require(BROWSER_CJS) as NomyoModule;
+
+    test('exposes the public API', () => {
+        expect(typeof nomyo.SecureChatCompletion).toBe('function');
+        expect(typeof nomyo.getMemoryProtectionInfo).toBe('function');
+    });
+
+    test('constructs a client without a DOM', () => {
+        const client = new nomyo.SecureChatCompletion({});
+        expect(client).toBeTruthy();
+        client.dispose();
+    });
+
+    test('reports browser memory protection', () => {
+        const info = nomyo.getMemoryProtectionInfo();
+        expect(info.canLock).toBe(false);
+        expect(info.method).toBe('zero-only');
+    });
+
+    test('carries no unresolved runtime requires', () => {
+        const source = fs.readFileSync(BROWSER_CJS, 'utf-8');
+        expect(source).not.toMatch(/require\(['"]\.\/node['"]\)/);
+        expect(source).not.toMatch(/require\(['"]\.\/browser['"]\)/);
+    });
+
+    test('does not drag the Node platform layer into the browser build', () => {
+        const source = fs.readFileSync(BROWSER_CJS, 'utf-8');
+        // The Node HTTP client and the optional native addon must not appear.
+        // `fs`/`path` legitimately do: KeyManager has Node-only branches guarded
+        // by `typeof window`, shared by both builds.
+        for (const nodeOnly of ['https', 'http', 'url', 'nomyo-native', 'node-gyp-build']) {
+            expect(source).not.toMatch(
+                new RegExp(`require\\(['"]${nodeOnly}['"]\\)`)
+            );
+        }
+    });
+});
+
+describeIfBuilt('built ESM entry point', () => {
+    test('is real ESM with an unambiguous extension', () => {
+        // A .js ES module in a non-"type":"module" package is parsed as
+        // CommonJS by Node and fails on older versions
+        expect(fs.existsSync(ESM_ENTRY)).toBe(true);
+        expect(fs.existsSync(path.join(DIST, 'esm', 'index.js'))).toBe(false);
+        expect(fs.readFileSync(ESM_ENTRY, 'utf-8')).toMatch(/^export |[\n;]export /);
+    });
+
+    test('shims require() for its lazily-loaded modules', () => {
+        // The source loads crypto/fs/path/jose/the native addon via require().
+        // `require` is not defined in ES module scope, so the bundle must
+        // provide it or those paths throw ReferenceError at runtime.
+        const source = fs.readFileSync(ESM_ENTRY, 'utf-8');
+        if (/[^.\w]require\(/.test(source)) {
+            expect(source).toMatch(/createRequire/);
+        }
+    });
+
+    test('is importable and usable by a real Node process', () => {
+        // Not `await import(...)` — ts-jest compiles dynamic import down to
+        // require() for its CommonJS target, which cannot load .mjs and would
+        // test the compiler rather than the bundle. Spawn Node instead.
+        const script = `import(${JSON.stringify(ESM_ENTRY)})`
+            + '.then(m => {'
+            + '  const c = new m.SecureChatCompletion({}); c.dispose();'
+            // Touches the require()-dependent crypto path
+            + '  if (typeof m.getMemoryProtectionInfo().method !== "string") process.exit(2);'
+            + '})'
+            + '.catch(e => { console.error(e.message); process.exit(3); })';
+
+        const result = spawnSync(process.execPath, ['--input-type=module', '-e', script], {
+            encoding: 'utf-8',
+        });
+
+        expect(result.stderr.trim()).toBe('');
+        expect(result.status).toBe(0);
+    });
+});
diff --git a/tests/setup.ts b/tests/setup.ts
new file mode 100644
index 0000000..d6e66dc
--- /dev/null
+++ b/tests/setup.ts
@@ -0,0 +1,14 @@
+/**
+ * Jest setup: register the Node.js platform implementations.
+ *
+ * The unit suites import core modules directly rather than going through the
+ * package entry point, so nothing would otherwise call registerSecureMemory /
+ * registerHttpClient. Importing src/node.ts performs that registration exactly
+ * as the published Node bundle does.
+ *
+ * Doing this here rather than falling back to a runtime `require('./node')`
+ * inside the core modules keeps that require out of the built bundles, where
+ * the relative path does not exist and bundlers would fail to resolve it.
+ */
+
+import '../src/node';