@void/react: a non-island component under an _-prefixed directory in pages/ ships every page module to the browser #575

Version: void / @void/react 1.2.1 (also 1.1.12); main at a6de782.

Repro

1. pnpm create void (React, static output: output: 'static' in void.config.ts).
2. pages/index.island.tsx:

   import { Frame } from './_ui/frame';
   export default function Home() { return <Frame><h1>Hello</h1></Frame>; }

3. pages/_ui/frame.tsx, a shared server-only component that is not a page or an island:

   export const SECRET_COPY = 'server-only text';
   export function Frame({ children }: { children: React.ReactNode }) {
     return <main data-x={SECRET_COPY}>{children}</main>;
   }

4. vp build, then ls dist/client/assets and grep -l 'server-only text' dist/client/assets/*.js.

Expected: an island-only app emits no pages-client bundle, and frame.tsx (not a route, because the route scanner skips _ segments) never reaches dist/client.

Actual: pages-client-*.js plus a chunk for every page module and every import (frame-*.js) are emitted to dist/client/assets, and the server-only strings are in them. In our app that is 18 files and 351 KB instead of 5 files and 33 KB, and 42 strings that were meant to stay server-side.

Cause: packages/react/src/plugin-pages.ts hasNonIslandPages() skips only basenames that start with _:

if (name.startsWith('_') || name.startsWith('layout.')) continue;

entry.name for pages/_ui/frame.tsx is frame.tsx. The pages scanner (scan.ts) skips any segment that starts with _ (except _layouts), so the two disagree. The Solid plugin has the same check.

Suggested fix: test every path segment relative to dir, as the scanner does:

const rel = relative(dir, join(entry.parentPath, name));
if (rel.split(sep).some((s) => s.startsWith('_')) || name.startsWith('layout.')) continue;

This is adjacent to #559, which adds the .server. exclusion to the same line.