fix(build/externals): honor thin wrappers for .js-suffixed subpaths

`bundlePackage` appended `.js` unconditionally when computing the
`src/external/{packageName}.js` wrapper path. For subpaths whose literal
name already ends in `.js` (e.g. `@npmcli/package-json/lib/read-package.js`
— the package's own exports map uses that literal path), this produced
`src/external/@npmcli/package-json/lib/read-package.js.js`, which
doesn't exist. `existsSync` returned false and the bundler silently
skipped the hand-written wrapper, bundling upstream directly. Any
customization intended for the wrapper layer (custom re-exports,
additional stubs) was invisibly discarded. Strips an existing `.js`
before appending so both subpath styles resolve to the same wrapper.

Author: jdalton

scripts/build-externals/bundler.mts

@@ -43,13 +43,15 @@ export async function bundlePackage(packageName, outputPath, options = {}) {
     let packagePath
 
     // First, check if src/external/{packageName}.js exists - use as entry point.
-    // Preserve scope for scoped packages like @socketregistry/yocto-spinner
-    const srcExternalPath = path.join(
-      rootDir,
-      'src',
-      'external',
-      `${packageName}.js`,
-    )
+    // Preserve scope for scoped packages like @socketregistry/yocto-spinner.
+    // Subpath entries may already end in `.js` (e.g. `@npmcli/package-json/
+    // lib/read-package.js` — the package's own exports map uses that literal
+    // path). Strip an existing `.js` before appending so we don't look for
+    // `read-package.js.js` and silently skip the thin wrapper.
+    const wrapperName = packageName.endsWith('.js')
+      ? packageName
+      : `${packageName}.js`
+    const srcExternalPath = path.join(rootDir, 'src', 'external', wrapperName)
     if (existsSync(srcExternalPath)) {
       packagePath = srcExternalPath
       if (!quiet) {