feat(desktop): add client extension points

desktop/vite.config.ts

@@ -2,6 +2,25 @@ import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 import path from 'path'
 
+// '@product' resolves to the built-in default (empty). An alternate build
+// can set COW_PRODUCT_DIR to point at another module instead.
+const productDir =
+  process.env.COW_PRODUCT_DIR || path.resolve(__dirname, 'src/renderer/src/product/default')
+
+// When '@product' points outside this project, its files can't resolve shared
+// deps from their own tree. Alias the shared runtime deps to this project's
+// node_modules so an out-of-tree product module imports the same instances.
+const nodeModules = path.resolve(__dirname, 'node_modules')
+const sharedDepAliases = process.env.COW_PRODUCT_DIR
+  ? {
+      react: path.join(nodeModules, 'react'),
+      'react-dom': path.join(nodeModules, 'react-dom'),
+      'react/jsx-runtime': path.join(nodeModules, 'react/jsx-runtime'),
+      'react-router-dom': path.join(nodeModules, 'react-router-dom'),
+      'lucide-react': path.join(nodeModules, 'lucide-react'),
+    }
+  : {}
+
 export default defineConfig({
   plugins: [react()],
   root: path.resolve(__dirname, 'src/renderer'),
@@ -17,6 +36,8 @@ export default defineConfig({
   resolve: {
     alias: {
       '@': path.resolve(__dirname, 'src/renderer/src'),
+      '@product': productDir,
+      ...sharedDepAliases,
     },
   },
 })