Fix SSR runtime failures: Node renderer, polyfills, and RSC classification

Three root causes for the 37/38 rspec test failures:

1. CI missing Node renderer: The RSC branch switched SSR from ExecJS to
   the react-on-rails-pro NodeRenderer service (port 3800). CI never
   started this service, causing Net::ReadTimeout on all SSR requests.
   Added renderer startup step and RENDERER_PASSWORD env var to CI.

2. Server bundle externals broke in VM sandbox: The previous commit
   externalized Node builtins (path/fs/stream) as CommonJS requires,
   but the Node renderer runs bundles in a vm.createContext() sandbox
   where require() is unavailable. Reverted to resolve.fallback: false
   which stubs these unused code paths at build time instead.

3. MessageChannel undefined in VM: react-dom/server.browser.js
   instantiates MessageChannel at module load time. The Node renderer's
   VM sandbox lacks this browser global (unlike Bun/ExecJS on master).
   Added a BannerPlugin polyfill injected at bundle top.

4. RouterApp.server.jsx misclassified as RSC: The auto-bundling system
   registered it via registerServerComponent() because it lacked 'use
   client'. But it's a traditional SSR component (StaticRouter), not an
   RSC. Added 'use client' directive so it registers via
   ReactOnRails.register() instead.

All 38 rspec tests now pass locally.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: justin808

.github/workflows/rspec_test.yml

@@ -33,6 +33,7 @@ jobs:
       DRIVER: selenium_chrome
       CHROME_BIN: /usr/bin/google-chrome
       USE_COVERALLS: true
+      RENDERER_PASSWORD: devPassword
 
     steps:
       - name: Install Chrome
@@ -82,6 +83,20 @@ jobs:
       - name: Build shakapacker chunks
         run: NODE_ENV=development bundle exec bin/shakapacker
 
+      - name: Start Node renderer for SSR
+        run: |
+          node react-on-rails-pro-node-renderer.js &
+          echo "Waiting for Node renderer on port 3800..."
+          for i in $(seq 1 30); do
+            if nc -z localhost 3800 2>/dev/null; then
+              echo "Node renderer is ready"
+              exit 0
+            fi
+            sleep 1
+          done
+          echo "Node renderer failed to start within 30 seconds"
+          exit 1
+
       - name: Run rspec with xvfb
         uses: coactions/setup-xvfb@v1
         with:

client/app/bundles/comments/startup/RouterApp/ror_components/RouterApp.server.jsx

@@ -1,3 +1,5 @@
+'use client';
+
 // Compare to ./RouterApp.client.jsx
 import { Provider } from 'react-redux';
 import React from 'react';

config/webpack/serverWebpackConfig.js

@@ -162,26 +162,39 @@ const configureServer = () => {
   // The default of cheap-module-source-map is slow and provides poor info.
   serverWebpackConfig.devtool = 'eval';
 
-  // Alias react-dom/server to the Node.js version for the Pro Node renderer.
-  // The default browser version uses MessageChannel which isn't available in the Node VM.
+  // react-on-rails-pro includes RSC-related modules that import Node.js builtins
+  // (path, fs, stream). These code paths aren't exercised in the SSR bundle,
+  // so provide empty fallbacks to satisfy the resolver without bundling them.
   serverWebpackConfig.resolve = serverWebpackConfig.resolve || {};
-  serverWebpackConfig.resolve.alias = {
-    ...serverWebpackConfig.resolve.alias,
-    'react-dom/server.browser$': 'react-dom/server.node',
-    'react-dom/server.browser.js$': 'react-dom/server.node.js',
+  serverWebpackConfig.resolve.fallback = {
+    ...serverWebpackConfig.resolve.fallback,
+    path: false,
+    fs: false,
+    'fs/promises': false,
+    stream: false,
   };
 
-  // react-on-rails-pro includes RSC-related modules that import Node.js builtins
-  // (path, fs, stream). Externalize them so they resolve at runtime via require()
-  // in the Node.js environment where the SSR bundle executes.
-  const existingExternals = serverWebpackConfig.externals || {};
-  serverWebpackConfig.externals = {
-    ...(typeof existingExternals === 'object' && !Array.isArray(existingExternals) ? existingExternals : {}),
-    path: 'commonjs path',
-    fs: 'commonjs fs',
-    'fs/promises': 'commonjs fs/promises',
-    stream: 'commonjs stream',
-  };
+  // The Node renderer runs bundles in a VM sandbox that lacks browser globals
+  // like MessageChannel and TextEncoder. Inject polyfills at the top of the
+  // bundle so react-dom/server.browser can initialize.
+  serverWebpackConfig.plugins.push(
+    new bundler.BannerPlugin({
+      banner: [
+        'if(typeof MessageChannel==="undefined"){',
+        '  globalThis.MessageChannel=class MessageChannel{',
+        '    constructor(){',
+        '      this.port1={onmessage:null};',
+        '      this.port2={postMessage:function(msg){',
+        '        var p=this._port1;if(p.onmessage)p.onmessage({data:msg});',
+        '      }};',
+        '      this.port2._port1=this.port1;',
+        '    }',
+        '  };',
+        '}',
+      ].join('\n'),
+      raw: true,
+    }),
+  );
 
   return serverWebpackConfig;
 };