Guard Vite API proxy setup behind VUE_APP_API_URL and reuse it in preview

Co-Authored-By: Codex <codex@openai.com>

vite.config.js

@@ -14,8 +14,31 @@ import { fileURLToPath, URL } from "node:url";
 import { defineConfig, loadEnv } from "vite";
 import vue from "@vitejs/plugin-vue";
 
+/**
+ * Builds Vite proxy configuration when backend target is available.
+ * @param {Record<string, string>} env - Loaded environment variables.
+ * @returns {Record<string, object>|undefined} Proxy config, or undefined when no target is configured.
+ */
+function createApiProxy(env) {
+  if (!env.VUE_APP_API_URL) {
+    console.warn(
+      "[vite] VUE_APP_API_URL is not set; /api proxy is disabled for this run.",
+    );
+    return undefined;
+  }
+
+  return {
+    "/api": {
+      target: env.VUE_APP_API_URL,
+      changeOrigin: true,
+      rewrite: (path) => path.replace(/^\/api/, ""),
+    },
+  };
+}
+
 export default defineConfig(({ mode }) => {
   const env = loadEnv(mode, process.cwd());
+  const proxy = createApiProxy(env);
 
   return {
     cacheDir: env.VITE_CACHE_DIR || undefined,
@@ -31,13 +54,12 @@ export default defineConfig(({ mode }) => {
     server: {
       host: "localhost",
       port: 58249,
-      proxy: {
-        "/api": {
-          target: env.VUE_APP_API_URL,
-          changeOrigin: true,
-          rewrite: (path) => path.replace(/^\/api/, ""),
-        },
-      },
+      proxy,
+    },
+    preview: {
+      host: "localhost",
+      port: 4173,
+      proxy,
     },
     optimizeDeps: {
       include: ["vue", "vue-router", "pinia", "axios"],