perf(dev): bundle dev server with webpack and add bytecode caching

- Bundle start-server.ts and dependencies with webpack for faster loading
- Add V8 bytecode caching to cache compiled code between runs
- Bytecode cache includes JIT warmup for optimal performance
- Cache stored in .next/cache/bytecode/ with automatic invalidation

This further reduces warm start time by ~50-100ms.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: feedthejim

packages/next/next-dev-server.webpack-config.js

@@ -0,0 +1,246 @@
+/**
+ * Webpack/Rspack config for bundling dev server startup modules.
+ *
+ * This bundles start-server.ts, router-server.ts, and their dependencies
+ * into a single file to reduce module loading overhead during dev server boot.
+ */
+
+/* eslint-disable import/no-extraneous-dependencies */
+const rspack = require('@rspack/core')
+const path = require('path')
+const { BundleAnalyzerPlugin } = require('webpack-bundle-analyzer')
+/* eslint-enable import/no-extraneous-dependencies */
+
+// Shared externals with the server runtime bundle
+const sharedExternals = [
+  'styled-jsx',
+  'styled-jsx/style',
+  '@opentelemetry/api',
+  'next/dist/compiled/@ampproject/toolbox-optimizer',
+  'next/dist/compiled/edge-runtime',
+  'next/dist/compiled/@edge-runtime/ponyfill',
+  'next/dist/compiled/undici',
+  'next/dist/compiled/raw-body',
+  'next/dist/server/capsize-font-metrics.json',
+  'critters',
+  'next/dist/compiled/node-html-parser',
+  'next/dist/compiled/compression',
+  'next/dist/compiled/jsonwebtoken',
+  'next/dist/compiled/@opentelemetry/api',
+  'next/dist/compiled/@mswjs/interceptors/ClientRequest',
+  'next/dist/compiled/ws',
+]
+
+// Dev server specific externals
+const devServerExternals = [
+  // Native bindings - cannot be bundled
+  '@next/swc',
+  // User-facing packages
+  '@next/env',
+  // Optional/native image dependencies
+  'sharp',
+]
+
+// Patterns to externalize
+const externalPatterns = [
+  // Pre-compiled dependencies
+  /^next\/dist\/compiled\//,
+  // Telemetry - lazy loaded
+  /telemetry\/storage/,
+  // Hot reloaders - dynamically loaded based on bundler choice
+  /hot-reloader-turbopack/,
+  /hot-reloader-webpack/,
+  /hot-reloader-rspack/,
+  // Turbopack internals - native bindings
+  /turbopack/,
+  // SWC bindings - native (matches ./swc, build/swc, etc.)
+  /\/swc($|\/)/,
+  // Sandbox - manipulates require.cache
+  /web\/sandbox/,
+  // Require hook - uses require.resolve with user-facing packages
+  /require-hook/,
+  // Config utils - uses require.resolve with dynamic webpack paths
+  /config-utils/,
+  // Config loading - uses dynamic import() for user config files
+  /\/config$/,
+  // Node environment extensions - sets up global handlers, avoid duplication
+  /node-environment-extensions/,
+  // TypeScript setup verification - uses dynamic require.resolve
+  /verify-typescript-setup/,
+  // Sharp image processing
+  /@img\/sharp/,
+]
+
+// Map relative paths to proper external paths
+// Note: Most mappings are now handled dynamically by toNextDistPath() in the externalHandler
+const externalsMap = {
+  // render-server pulls in next-server which has heavy dependencies (react-dom/server)
+  // It's lazy-loaded at runtime when handling requests, not at startup
+  './render-server': 'next/dist/server/lib/render-server',
+  '../render-server': 'next/dist/server/lib/render-server',
+  // next/dist/server/next (the main Next.js server) - heavy, only needed for request handling
+  '../next': 'next/dist/server/next',
+}
+
+// Regex-based externals mapping
+const externalsRegexMap = {
+  '(.*)trace/tracer$': 'next/dist/server/lib/trace/tracer',
+}
+
+/**
+ * Convert an absolute path within dist/ to a next/dist/... style import
+ * @param {string} absolutePath
+ * @returns {string|null}
+ */
+function toNextDistPath(absolutePath) {
+  const normalizedPath = absolutePath.replace(/\\/g, '/')
+  const distIndex = normalizedPath.indexOf('/dist/')
+  if (distIndex === -1) return null
+
+  // Get the path after /dist/ and convert to next/dist/...
+  const relativePath = normalizedPath.substring(distIndex + 1) // removes leading /
+  return `next/${relativePath.replace(/\.js$/, '')}`
+}
+
+/**
+ * @param {Object} options
+ * @param {boolean} options.dev - Development mode
+ * @returns {import('@rspack/core').Configuration}
+ */
+module.exports = ({ dev }) => {
+  const externalHandler = ({ context, request, getResolve }, callback) => {
+    ;(async () => {
+      // Handle compiled dependencies with complex paths
+      if (
+        request.match(
+          /next[/\\]dist[/\\]compiled[/\\](babel|webpack|source-map|semver|jest-worker|stacktrace-parser|@ampproject\/toolbox-optimizer)/
+        )
+      ) {
+        callback(null, 'commonjs ' + request)
+        return
+      }
+
+      // Handle image optimizer and test mode
+      if (request.match(/(server\/image-optimizer|experimental\/testmode)/)) {
+        callback(null, 'commonjs ' + request)
+        return
+      }
+
+      // Handle .external.js files
+      if (request.match(/\.external(\.js)?$/)) {
+        const resolve = getResolve()
+        const resolved = await resolve(context, request)
+        const nextDistPath = toNextDistPath(resolved)
+        if (nextDistPath) {
+          callback(null, `commonjs ${nextDistPath}`)
+          return
+        }
+        callback(null, `commonjs ${request}`)
+        return
+      }
+
+      // Handle pattern-based externals - resolve and convert to next/dist/... paths
+      for (const pattern of externalPatterns) {
+        if (pattern.test(request)) {
+          // Try to resolve and get proper next/dist/... path
+          try {
+            const resolve = getResolve()
+            const resolved = await resolve(context, request)
+            const nextDistPath = toNextDistPath(resolved)
+            if (nextDistPath) {
+              callback(null, `commonjs ${nextDistPath}`)
+              return
+            }
+          } catch {
+            // Resolution failed, use request as-is
+          }
+          callback(null, 'commonjs ' + request)
+          return
+        }
+      }
+
+      // Handle regex map externals
+      const regexMatch = Object.keys(externalsRegexMap).find((regex) =>
+        new RegExp(regex).test(request)
+      )
+      if (regexMatch) {
+        callback(null, 'commonjs ' + externalsRegexMap[regexMatch])
+        return
+      }
+
+      callback()
+    })()
+  }
+
+  return {
+    entry: {
+      'start-server': path.join(__dirname, 'dist/server/lib/start-server.js'),
+    },
+    target: 'node',
+    mode: dev ? 'development' : 'production',
+    output: {
+      path: path.join(__dirname, 'dist/compiled/dev-server'),
+      filename: '[name].js',
+      libraryTarget: 'commonjs2',
+    },
+    devtool: dev ? 'source-map' : false,
+    optimization: {
+      moduleIds: 'named',
+      minimize: !dev,
+      ...(dev
+        ? {}
+        : {
+            minimizer: [
+              new rspack.SwcJsMinimizerRspackPlugin({
+                minimizerOptions: {
+                  mangle: false, // Keep readable for debugging
+                },
+              }),
+            ],
+          }),
+    },
+    plugins: [
+      new rspack.DefinePlugin({
+        'typeof window': JSON.stringify('undefined'),
+        'process.env.NODE_ENV': JSON.stringify(
+          dev ? 'development' : 'production'
+        ),
+      }),
+      new rspack.BannerPlugin({
+        banner: '/* Bundled dev server - reduces module loading overhead */',
+        raw: true,
+      }),
+      process.env.ANALYZE &&
+        new BundleAnalyzerPlugin({
+          analyzerMode: 'static',
+          reportFilename: path.join(
+            __dirname,
+            'dist/compiled/dev-server/bundle-report.html'
+          ),
+          openAnalyzer: false,
+        }),
+    ].filter(Boolean),
+    resolve: {
+      extensions: ['.js', '.json'],
+    },
+    externals: [
+      ...sharedExternals,
+      ...devServerExternals,
+      externalsMap,
+      externalHandler,
+    ],
+    externalsPresets: {
+      node: true,
+    },
+    stats: process.env.ANALYZE_REASONS
+      ? {
+          preset: 'verbose',
+          reasons: true,
+          modulesSpace: Infinity,
+        }
+      : {
+          preset: 'errors-warnings',
+          assets: true,
+        },
+  }
+}