diff --git a/packages/react/src/plugin-pages.ts b/packages/react/src/plugin-pages.ts
index 8746022b3..372098274 100644
--- a/packages/react/src/plugin-pages.ts
+++ b/packages/react/src/plugin-pages.ts
@@ -1,4 +1,4 @@
-import { existsSync, readdirSync } from 'node:fs';
+import { existsSync } from 'node:fs';
 import { dirname, relative } from 'pathslash';
 import { normalizePath, type Plugin, type ResolvedConfig, type ViteDevServer } from 'vite';
 import {
@@ -38,33 +38,6 @@ type PagesPluginOptions = {
   prefetch?: PrefetchConfig;
 };
 
-/** Check if the pages directory has any page components that need the full client runtime. */
-function hasNonIslandPages(dir: string): boolean {
-  try {
-    for (const entry of readdirSync(dir, { withFileTypes: true, recursive: true })) {
-      if (!entry.isFile()) {
-        continue;
-      }
-      const name = entry.name;
-      // Server companions such as `index.server.tsx` are not pages.
-      if (
-        name.startsWith('_') ||
-        name.startsWith('layout.') ||
-        name.endsWith('.server.tsx') ||
-        name.endsWith('.server.jsx')
-      ) {
-        continue;
-      }
-      if (/\.(tsx|jsx)$/.test(name) && !name.includes('.island.')) {
-        return true;
-      }
-    }
-  } catch {
-    // ignore
-  }
-  return false;
-}
-
 export function pagesPlugin(pagesDir: string, options?: PagesPluginOptions): Plugin {
   let pageScan: PageScanResult | null = null;
   let isDev = false;
@@ -175,7 +148,7 @@ export function pagesPlugin(pagesDir: string, options?: PagesPluginOptions): Plu
       viteConfig = config;
     },
 
-    config(_, env) {
+    async config(_, env) {
       // Set before the early return: pages/ may be created after the server starts.
       isDev = env.command === 'serve';
       if (!existsSync(pagesDir)) {
@@ -220,7 +193,8 @@ export function pagesPlugin(pagesDir: string, options?: PagesPluginOptions): Plu
       }
 
       // Skip the pages-client bundle when all pages are island pages
-      if (!hasNonIslandPages(pagesDir)) {
+      await runRescan();
+      if (!pageScan?.pages.some((page) => !page.island)) {
         return;
       }
 
diff --git a/packages/react/test/integration/island-css-build.test.ts b/packages/react/test/integration/island-css-build.test.ts
index 97149f117..4c13079c5 100644
--- a/packages/react/test/integration/island-css-build.test.ts
+++ b/packages/react/test/integration/island-css-build.test.ts
@@ -1,6 +1,7 @@
 import { join } from 'node:path';
 import { expect, it } from 'vite-plus/test';
 import { buildIslandApp, defineIslandCssBuildTest } from '../../../../test/island-css-build.ts';
+import { definePrivatePagesBuildTest } from '../../../../test/private-pages-build.ts';
 
 const packageDir = join(import.meta.dirname, '../..');
 const tsconfig = JSON.stringify({ compilerOptions: { jsx: 'react-jsx' } });
@@ -79,3 +80,13 @@ export default function Home() { return <Counter />; }`,
     build.cleanup();
   }
 }, 120_000);
+
+definePrivatePagesBuildTest({
+  packageDir,
+  pluginName: 'voidReact',
+  counter: `import { useState } from 'react';
+export default function Counter() {
+  const [count, setCount] = useState(0);
+  return <button onClick={() => setCount(count + 1)}>Count: {count}</button>;
+}`,
+});
diff --git a/packages/react/test/unit/plugin-pages.test.ts b/packages/react/test/unit/plugin-pages.test.ts
index d297b80b4..365027e65 100644
--- a/packages/react/test/unit/plugin-pages.test.ts
+++ b/packages/react/test/unit/plugin-pages.test.ts
@@ -20,13 +20,13 @@ type PagesPluginHooks = {
     | HookWithHandler<(id: string) => Promise<string | undefined> | string | undefined>;
 };
 
-function loadServeConfig(): Record<string, unknown> {
+async function loadServeConfig(): Promise<Record<string, unknown>> {
   mkdirSync(PAGES_DIR, { recursive: true });
   const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
   if (typeof plugin.config === 'function') {
-    return plugin.config({}, { command: 'serve' }) as Record<string, unknown>;
+    return (await plugin.config({}, { command: 'serve' })) as Record<string, unknown>;
   }
-  return plugin.config?.handler({}, { command: 'serve' }) as Record<string, unknown>;
+  return (await plugin.config?.handler({}, { command: 'serve' })) as Record<string, unknown>;
 }
 
 function getHookHandler<T>(hook: T | HookWithHandler<T> | undefined): T {
@@ -68,34 +68,133 @@ describe('pagesPlugin build config', () => {
     rmSync(TMP, { recursive: true, force: true });
   });
 
+  it.each([
+    '_ui/frame.tsx',
+    'blog/_private/frame.jsx',
+    '_layouts/docs.tsx',
+    'blog/_layouts/docs.jsx',
+    '_helper.tsx',
+  ])('omits pages-client for an island-only app with %s', async (helper) => {
+    writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
+    writePage(
+      helper,
+      'export default function Helper(props) { return <main>{props.children}</main>; }',
+    );
+
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
+  });
+
+  it.each([
+    ['debug.dev.tsx', false],
+    ['debug.prod.tsx', true],
+  ] as const)('selects pages-client from production pages for %s', async (page, included) => {
+    writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
+    writePage(page, 'export default function Debug() { return <p>Debug</p>; }');
+
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    const config = await getHookHandler(plugin.config)({}, { command: 'build' });
+    if (included) {
+      expect(config).toMatchObject({
+        build: { rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } } },
+      });
+    } else {
+      expect(config).toBeUndefined();
+    }
+  });
+
+  it.each([false, true])(
+    'scans a custom pages root under an underscore path, ordinary page=%s',
+    async (ordinary) => {
+      const customPages = join(TMP, '_source', '_views');
+      mkdirSync(customPages, { recursive: true });
+      writeFileSync(
+        join(customPages, 'index.island.tsx'),
+        'export default function Home() { return <h1>Home</h1>; }',
+      );
+      if (ordinary) {
+        writeFileSync(
+          join(customPages, 'about.tsx'),
+          'export default function About() { return <p>About</p>; }',
+        );
+      }
+
+      const plugin = pagesPlugin(customPages, { root: TMP }) as PagesPluginHooks;
+      const config = await getHookHandler(plugin.config)({}, { command: 'build' });
+      if (ordinary) {
+        expect(config).toMatchObject({
+          build: { rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } } },
+        });
+      } else {
+        expect(config).toBeUndefined();
+      }
+    },
+  );
+
+  it('omits pages-client for Markdown pages', async () => {
+    writePage('index.md', '# Home');
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
+  });
+
+  it.each([
+    ['other.vue', '<template><p>Other</p></template>'],
+    ['other.svelte', '<p>Other</p>'],
+  ])('uses the scanner inventory for a non-island %s component', async (page, component) => {
+    writePage(page, component);
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toMatchObject({
+      build: { rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } } },
+    });
+  });
+
+  it('returns no build config when the pages directory is missing', async () => {
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
+  });
+
+  it('reports invalid production routes during build configuration', async () => {
+    writePage('index.tsx', 'export default function Home() { return <h1>Home</h1>; }');
+    writePage('index.jsx', 'export default function Duplicate() { return <h1>Duplicate</h1>; }');
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    await expect(getHookHandler(plugin.config)({}, { command: 'build' })).rejects.toThrow(
+      'Multiple page files resolve to the same route',
+    );
+  });
+
   it.each(['tsx', 'jsx'])(
     'omits pages-client for island-only pages with .server.%s files',
-    (extension) => {
+    async (extension) => {
       writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
       writePage(`index.server.${extension}`, 'export const loader = () => ({ count: 0 });');
 
       const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-      expect(getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
+      expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
     },
   );
 
-  it.each(['about.tsx', 'about.jsx', 'blog/about.tsx', 'blog/about.jsx', 'status.server.v2.tsx'])(
-    'keeps pages-client for an ordinary %s page alongside island pages',
-    (page) => {
-      writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
-      writePage('index.server.tsx', 'export const loader = () => ({});');
-      writePage('index.server.jsx', 'export const loader = () => ({});');
-      writePage(page, 'export default function About() { return <h1>About</h1>; }');
+  it.each([
+    'about.tsx',
+    'about.jsx',
+    'blog/about.tsx',
+    'blog/about.jsx',
+    'status.server.v2.tsx',
+    'status.island.v2.tsx',
+    'layout.extra.tsx',
+  ])('keeps pages-client for an ordinary %s page alongside island pages', async (page) => {
+    writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
+    writePage('index.server.tsx', 'export const loader = () => ({});');
+    writePage('index.server.jsx', 'export const loader = () => ({});');
+    writePage(page, 'export default function About() { return <h1>About</h1>; }');
 
-      const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-      expect(getHookHandler(plugin.config)({}, { command: 'build' })).toMatchObject({
-        build: {
-          manifest: true,
-          rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } },
-        },
-      });
-    },
-  );
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toMatchObject({
+      build: {
+        manifest: true,
+        rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } },
+      },
+    });
+  });
 });
 
 describe('pagesPlugin dev config', () => {
@@ -103,8 +202,8 @@ describe('pagesPlugin dev config', () => {
     rmSync(TMP, { recursive: true, force: true });
   });
 
-  it('pre-optimizes React dependencies in the Cloudflare worker environment', () => {
-    const config = loadServeConfig();
+  it('pre-optimizes React dependencies in the Cloudflare worker environment', async () => {
+    const config = await loadServeConfig();
 
     expect(config).toMatchObject({
       environments: {
@@ -124,8 +223,8 @@ describe('pagesPlugin dev config', () => {
     });
   });
 
-  it('includes only the React entry points needed by each environment', () => {
-    const config = loadServeConfig() as {
+  it('includes only the React entry points needed by each environment', async () => {
+    const config = (await loadServeConfig()) as {
       optimizeDeps: { include: Array<string> };
       ssr?: { optimizeDeps?: { include?: Array<string> } };
       environments: {
@@ -151,7 +250,7 @@ describe('pagesPlugin dev config', () => {
     writePage('index.tsx', 'export default function Index() { return <h1>Home</h1>; }\n');
 
     const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-    getHookHandler(plugin.config)({}, { command: 'serve' });
+    await getHookHandler(plugin.config)({}, { command: 'serve' });
     await getHookHandler(plugin.buildStart).call({});
     const handlers = setupWatcher(plugin);
 
@@ -170,7 +269,7 @@ describe('pagesPlugin dev config', () => {
     writePage('index.tsx', 'export default function Index() { return <h1>Home</h1>; }\n');
 
     const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-    getHookHandler(plugin.config)({}, { command: 'serve' });
+    await getHookHandler(plugin.config)({}, { command: 'serve' });
     await getHookHandler(plugin.buildStart).call({});
     const logError = vi.fn();
     const invalidateModule = vi.fn();
@@ -218,7 +317,7 @@ describe('pagesPlugin environment suffixes', () => {
 
   async function loadModules(command: 'serve' | 'build') {
     const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-    getHookHandler(plugin.config)({}, { command });
+    await getHookHandler(plugin.config)({}, { command });
     await getHookHandler(plugin.buildStart).call({});
     const load = getHookHandler(plugin.load);
     return {
@@ -254,7 +353,7 @@ describe('pagesPlugin environment suffixes', () => {
 
   it('scans for dev when pages/ is created after the serve config', async () => {
     const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-    expect(getHookHandler(plugin.config)({}, { command: 'serve' })).toBeUndefined();
+    expect(await getHookHandler(plugin.config)({}, { command: 'serve' })).toBeUndefined();
 
     writePage('debug.dev.tsx', 'export default function Debug() { return <h1>Debug</h1>; }\n');
     await getHookHandler(plugin.buildStart).call({});
diff --git a/packages/solid/src/plugin-pages.ts b/packages/solid/src/plugin-pages.ts
index 65899de54..74bfc4afe 100644
--- a/packages/solid/src/plugin-pages.ts
+++ b/packages/solid/src/plugin-pages.ts
@@ -1,4 +1,4 @@
-import { existsSync, readdirSync } from 'node:fs';
+import { existsSync } from 'node:fs';
 import { dirname } from 'pathslash';
 import { normalizePath, type Plugin, type ResolvedConfig, type ViteDevServer } from 'vite';
 import {
@@ -22,33 +22,6 @@ type PagesPluginOptions = {
   prefetch?: PrefetchConfig;
 };
 
-/** Check if the pages directory has any page components that need the full client runtime. */
-function hasNonIslandPages(dir: string): boolean {
-  try {
-    for (const entry of readdirSync(dir, { withFileTypes: true, recursive: true })) {
-      if (!entry.isFile()) {
-        continue;
-      }
-      const name = entry.name;
-      // Server companions such as `index.server.tsx` are not pages.
-      if (
-        name.startsWith('_') ||
-        name.startsWith('layout.') ||
-        name.endsWith('.server.tsx') ||
-        name.endsWith('.server.jsx')
-      ) {
-        continue;
-      }
-      if (/\.(tsx|jsx)$/.test(name) && !name.includes('.island.')) {
-        return true;
-      }
-    }
-  } catch {
-    // ignore
-  }
-  return false;
-}
-
 export function pagesPlugin(pagesDir: string, options?: PagesPluginOptions): Plugin {
   let pageScan: PageScanResult | null = null;
   let isDev = false;
@@ -158,7 +131,7 @@ export function pagesPlugin(pagesDir: string, options?: PagesPluginOptions): Plu
       viteConfig = config;
     },
 
-    config(_, env) {
+    async config(_, env) {
       // Set before the early return: pages/ may be created after the server starts.
       isDev = env.command === 'serve';
       if (!existsSync(pagesDir)) {
@@ -175,7 +148,8 @@ export function pagesPlugin(pagesDir: string, options?: PagesPluginOptions): Plu
       }
 
       // Skip the pages-client bundle when all pages are island pages
-      if (!hasNonIslandPages(pagesDir)) {
+      await runRescan();
+      if (!pageScan?.pages.some((page) => !page.island)) {
         return;
       }
 
diff --git a/packages/solid/test/integration/island-css-build.test.ts b/packages/solid/test/integration/island-css-build.test.ts
index 0df086474..b621266fe 100644
--- a/packages/solid/test/integration/island-css-build.test.ts
+++ b/packages/solid/test/integration/island-css-build.test.ts
@@ -1,5 +1,6 @@
 import { join } from 'node:path';
 import { defineIslandCssBuildTest } from '../../../../test/island-css-build.ts';
+import { definePrivatePagesBuildTest } from '../../../../test/private-pages-build.ts';
 
 defineIslandCssBuildTest({
   packageDir: join(import.meta.dirname, '../..'),
@@ -28,3 +29,13 @@ export default function BadgePage() { return <Badge />; }`,
   },
   expectedCss: ['.shell{outline-offset:7px}', '{text-indent:9px}', '.badge{word-spacing:5px}'],
 });
+
+definePrivatePagesBuildTest({
+  packageDir: join(import.meta.dirname, '../..'),
+  pluginName: 'voidSolid',
+  counter: `import { createSignal } from 'solid-js';
+export default function Counter() {
+  const [count, setCount] = createSignal(0);
+  return <button onClick={() => setCount(count() + 1)}>Count: {count()}</button>;
+}`,
+});
diff --git a/packages/solid/test/unit/plugin-pages.test.ts b/packages/solid/test/unit/plugin-pages.test.ts
index 632ee463f..16062582a 100644
--- a/packages/solid/test/unit/plugin-pages.test.ts
+++ b/packages/solid/test/unit/plugin-pages.test.ts
@@ -59,34 +59,133 @@ describe('pagesPlugin build config', () => {
     rmSync(TMP, { recursive: true, force: true });
   });
 
+  it.each([
+    '_ui/frame.tsx',
+    'blog/_private/frame.jsx',
+    '_layouts/docs.tsx',
+    'blog/_layouts/docs.jsx',
+    '_helper.tsx',
+  ])('omits pages-client for an island-only app with %s', async (helper) => {
+    writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
+    writePage(
+      helper,
+      'export default function Helper(props) { return <main>{props.children}</main>; }',
+    );
+
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
+  });
+
+  it.each([
+    ['debug.dev.tsx', false],
+    ['debug.prod.tsx', true],
+  ] as const)('selects pages-client from production pages for %s', async (page, included) => {
+    writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
+    writePage(page, 'export default function Debug() { return <p>Debug</p>; }');
+
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    const config = await getHookHandler(plugin.config)({}, { command: 'build' });
+    if (included) {
+      expect(config).toMatchObject({
+        build: { rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } } },
+      });
+    } else {
+      expect(config).toBeUndefined();
+    }
+  });
+
+  it.each([false, true])(
+    'scans a custom pages root under an underscore path, ordinary page=%s',
+    async (ordinary) => {
+      const customPages = join(TMP, '_source', '_views');
+      mkdirSync(customPages, { recursive: true });
+      writeFileSync(
+        join(customPages, 'index.island.tsx'),
+        'export default function Home() { return <h1>Home</h1>; }',
+      );
+      if (ordinary) {
+        writeFileSync(
+          join(customPages, 'about.tsx'),
+          'export default function About() { return <p>About</p>; }',
+        );
+      }
+
+      const plugin = pagesPlugin(customPages, { root: TMP }) as PagesPluginHooks;
+      const config = await getHookHandler(plugin.config)({}, { command: 'build' });
+      if (ordinary) {
+        expect(config).toMatchObject({
+          build: { rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } } },
+        });
+      } else {
+        expect(config).toBeUndefined();
+      }
+    },
+  );
+
+  it('omits pages-client for Markdown pages', async () => {
+    writePage('index.md', '# Home');
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
+  });
+
+  it.each([
+    ['other.vue', '<template><p>Other</p></template>'],
+    ['other.svelte', '<p>Other</p>'],
+  ])('uses the scanner inventory for a non-island %s component', async (page, component) => {
+    writePage(page, component);
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toMatchObject({
+      build: { rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } } },
+    });
+  });
+
+  it('returns no build config when the pages directory is missing', async () => {
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
+  });
+
+  it('reports invalid production routes during build configuration', async () => {
+    writePage('index.tsx', 'export default function Home() { return <h1>Home</h1>; }');
+    writePage('index.jsx', 'export default function Duplicate() { return <h1>Duplicate</h1>; }');
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    await expect(getHookHandler(plugin.config)({}, { command: 'build' })).rejects.toThrow(
+      'Multiple page files resolve to the same route',
+    );
+  });
+
   it.each(['tsx', 'jsx'])(
     'omits pages-client for island-only pages with .server.%s files',
-    (extension) => {
+    async (extension) => {
       writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
       writePage(`index.server.${extension}`, 'export const loader = () => ({ count: 0 });');
 
       const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-      expect(getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
+      expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toBeUndefined();
     },
   );
 
-  it.each(['about.tsx', 'about.jsx', 'blog/about.tsx', 'blog/about.jsx', 'status.server.v2.tsx'])(
-    'keeps pages-client for an ordinary %s page alongside island pages',
-    (page) => {
-      writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
-      writePage('index.server.tsx', 'export const loader = () => ({});');
-      writePage('index.server.jsx', 'export const loader = () => ({});');
-      writePage(page, 'export default function About() { return <h1>About</h1>; }');
+  it.each([
+    'about.tsx',
+    'about.jsx',
+    'blog/about.tsx',
+    'blog/about.jsx',
+    'status.server.v2.tsx',
+    'status.island.v2.tsx',
+    'layout.extra.tsx',
+  ])('keeps pages-client for an ordinary %s page alongside island pages', async (page) => {
+    writePage('index.island.tsx', 'export default function Home() { return <h1>Home</h1>; }');
+    writePage('index.server.tsx', 'export const loader = () => ({});');
+    writePage('index.server.jsx', 'export const loader = () => ({});');
+    writePage(page, 'export default function About() { return <h1>About</h1>; }');
 
-      const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-      expect(getHookHandler(plugin.config)({}, { command: 'build' })).toMatchObject({
-        build: {
-          manifest: true,
-          rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } },
-        },
-      });
-    },
-  );
+    const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
+    expect(await getHookHandler(plugin.config)({}, { command: 'build' })).toMatchObject({
+      build: {
+        manifest: true,
+        rollupOptions: { input: { 'pages-client': 'virtual:void-pages-client' } },
+      },
+    });
+  });
 });
 
 describe('pagesPlugin dev HMR', () => {
@@ -98,7 +197,7 @@ describe('pagesPlugin dev HMR', () => {
     writePage('index.tsx', 'export default function Index() { return <h1>Home</h1>; }\n');
 
     const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-    getHookHandler(plugin.config)({}, { command: 'serve' });
+    await getHookHandler(plugin.config)({}, { command: 'serve' });
     await getHookHandler(plugin.buildStart).call({});
     const handlers = setupWatcher(plugin);
 
@@ -117,7 +216,7 @@ describe('pagesPlugin dev HMR', () => {
     writePage('index.tsx', 'export default function Index() { return <h1>Home</h1>; }\n');
 
     const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-    getHookHandler(plugin.config)({}, { command: 'serve' });
+    await getHookHandler(plugin.config)({}, { command: 'serve' });
     await getHookHandler(plugin.buildStart).call({});
     const logError = vi.fn();
     const invalidateModule = vi.fn();
@@ -163,7 +262,7 @@ describe('pagesPlugin environment suffixes', () => {
     writePage('home.prod.tsx', 'export default function Page() { return <h1>Prod</h1>; }\n');
 
     const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-    getHookHandler(plugin.config)({}, { command: 'build' });
+    await getHookHandler(plugin.config)({}, { command: 'build' });
     await getHookHandler(plugin.buildStart).call({});
     const load = getHookHandler(plugin.load);
 
@@ -182,7 +281,7 @@ describe('pagesPlugin environment suffixes', () => {
     writePage('home.prod.tsx', 'export default function Page() { return <h1>Prod</h1>; }\n');
 
     const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-    getHookHandler(plugin.config)({}, { command: 'serve' });
+    await getHookHandler(plugin.config)({}, { command: 'serve' });
     await getHookHandler(plugin.buildStart).call({});
     const load = getHookHandler(plugin.load);
 
@@ -196,7 +295,7 @@ describe('pagesPlugin environment suffixes', () => {
 
   it('scans for dev when pages/ is created after the serve config', async () => {
     const plugin = pagesPlugin(PAGES_DIR) as PagesPluginHooks;
-    expect(getHookHandler(plugin.config)({}, { command: 'serve' })).toBeUndefined();
+    expect(await getHookHandler(plugin.config)({}, { command: 'serve' })).toBeUndefined();
 
     writePage('debug.dev.tsx', 'export default function Page() { return <h1>Debug</h1>; }\n');
     await getHookHandler(plugin.buildStart).call({});
diff --git a/test/private-pages-build.ts b/test/private-pages-build.ts
new file mode 100644
index 000000000..3d61b3cd4
--- /dev/null
+++ b/test/private-pages-build.ts
@@ -0,0 +1,92 @@
+import { readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { chromium, type Browser } from 'playwright';
+import { preview, type PreviewServer } from 'vite';
+import { expect, it } from 'vite-plus/test';
+import { waitForIslandsHydrated } from './browser-helpers.ts';
+import { buildIslandApp } from './island-css-build.ts';
+
+export function definePrivatePagesBuildTest(app: {
+  packageDir: string;
+  pluginName: 'voidReact' | 'voidSolid';
+  counter: string;
+}): void {
+  it('excludes private helpers from the Pages client and hydrates explicit private islands', async () => {
+    const classAttribute = app.pluginName === 'voidReact' ? 'className' : 'class';
+    const build = buildIslandApp({
+      packageDir: app.packageDir,
+      pluginName: app.pluginName,
+      files: {
+        'tsconfig.json': JSON.stringify({
+          compilerOptions: {
+            jsx: app.pluginName === 'voidReact' ? 'react-jsx' : 'preserve',
+            jsxImportSource: app.pluginName === 'voidReact' ? 'react' : 'solid-js',
+          },
+        }),
+        'pages/_ui/frame.tsx': `import './frame.css';
+export function Frame(props) {
+  return <main ${classAttribute}="private-frame" data-frame="575_SERVER_FRAME">{props.children}</main>;
+}`,
+        'pages/_ui/frame.css': '.private-frame { outline-offset: 11px; }',
+        'pages/_ui/counter.tsx': app.counter,
+        'pages/_layouts/docs.tsx': `import './docs.css';
+export default function Docs(props) {
+  return <section ${classAttribute}="private-layout" data-layout="docs">{props.children}</section>;
+}`,
+        'pages/_layouts/docs.css': '.private-layout { word-spacing: 3px; }',
+        'pages/index.island.tsx': `import { Frame } from './_ui/frame';
+import Counter from './_ui/counter' with { island: 'load' };
+export const layout = 'docs';
+export default function Home() { return <Frame><Counter /></Frame>; }`,
+      },
+    });
+    let server: PreviewServer | undefined;
+    let browser: Browser | undefined;
+    try {
+      const manifest = JSON.parse(
+        readFileSync(join(build.root, 'dist/client/.vite/manifest.json'), 'utf8'),
+      );
+      expect(Object.values(manifest)).not.toContainEqual(
+        expect.objectContaining({ name: 'pages-client', isEntry: true }),
+      );
+      expect(Object.values(manifest)).toContainEqual(
+        expect.objectContaining({ name: 'islands-client', isEntry: true }),
+      );
+      const { html, css } = build.page('index.html');
+      expect(html).toContain('data-frame="575_SERVER_FRAME"');
+      expect(html).toContain('data-layout="docs"');
+      expect(css).toContain('.private-frame{outline-offset:11px}');
+      expect(css).toContain('.private-layout{word-spacing:3px}');
+      for (const [file, text] of build.output('client')) {
+        if (file.endsWith('.js')) {
+          expect(text, file).not.toContain('575_SERVER_FRAME');
+        }
+      }
+
+      server = await preview({
+        root: build.root,
+        configFile: false,
+        logLevel: 'silent',
+        build: { outDir: 'dist/client' },
+        preview: { host: '127.0.0.1', port: 0 },
+      });
+      const base = server.resolvedUrls?.local[0];
+      if (!base) {
+        throw new Error('Preview did not report a local URL.');
+      }
+      browser = await chromium.launch();
+      const page = await browser.newPage();
+      const errors: Array<string> = [];
+      page.on('pageerror', (error) => errors.push(error.message));
+      await page.goto(base);
+      await waitForIslandsHydrated(page, 1, 15_000);
+      await page.getByRole('button', { name: 'Count: 0', exact: true }).click();
+      await expect.poll(() => page.getByRole('button').textContent()).toBe('Count: 1');
+      expect(errors).toEqual([]);
+    } finally {
+      await browser?.close();
+      await server?.close();
+      build.cleanup();
+    }
+  }, 120_000);
+}