feat(devtools): migrate devtools package into monorepo (#18936)

packages/devtools/esbuild.client.js

@@ -0,0 +1,30 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import esbuild from 'esbuild';
+import { mkdirSync, readFileSync, writeFileSync } from 'node:fs';
+
+mkdirSync('dist/client', { recursive: true });
+
+await esbuild.build({
+  entryPoints: ['client/src/main.tsx'],
+  bundle: true,
+  minify: true,
+  format: 'esm',
+  target: 'es2020',
+  jsx: 'automatic',
+  outfile: 'dist/client/main.js',
+});
+
+// Embed client assets as string constants so the devtools server can be
+// bundled into the CLI without needing readFileSync + __dirname at runtime.
+const indexHtml = readFileSync('client/index.html', 'utf-8');
+const clientJs = readFileSync('dist/client/main.js', 'utf-8');
+
+writeFileSync(
+  'src/_client-assets.ts',
+  `/**\n * @license\n * Copyright 2025 Google LLC\n * SPDX-License-Identifier: Apache-2.0\n */\n\n// Auto-generated by esbuild.client.js — do not edit\nexport const INDEX_HTML = ${JSON.stringify(indexHtml)};\nexport const CLIENT_JS = ${JSON.stringify(clientJs)};\n`,
+);