feat: 完善 MVP-2 演示和进度体验

app/static/app.js

@@ -114,21 +114,43 @@ function pollTaskListStatus() {
 
 async function downloadExport(url, defaultFilename, event) {
   if (event) event.preventDefault();
-  const resp = await fetch(url);
-  if (!resp.ok) {
-    alert("导出失败，请稍后重试。");
-    return;
+  const button = event ? event.currentTarget : null;
+  const originalText = button ? button.textContent : "";
+  if (button) {
+    button.disabled = true;
+    button.textContent = "下载中...";
+  }
+  try {
+    const resp = await fetch(url, { cache: "no-store" });
+    if (!resp.ok) {
+      let message = "导出失败，请稍后重试。";
+      try {
+        const data = await resp.json();
+        if (data.detail) message = data.detail;
+      } catch (_error) {
+        message = resp.status === 503 ? "数据库暂时不可用，请稍后重试。" : message;
+      }
+      alert(message);
+      return;
+    }
+    const blob = await resp.blob();
+    const disposition = resp.headers.get("Content-Disposition") || "";
+    const match = disposition.match(/filename\*=UTF-8''([^;]+)/);
+    const filename = match ? decodeURIComponent(match[1]) : defaultFilename;
+    const blobUrl = URL.createObjectURL(blob);
+    const link = document.createElement("a");
+    link.href = blobUrl;
+    link.download = filename;
+    document.body.appendChild(link);
+    link.click();
+    document.body.removeChild(link);
+    URL.revokeObjectURL(blobUrl);
+  } catch (_error) {
+    alert("网络异常，导出未完成。");
+  } finally {
+    if (button) {
+      button.disabled = false;
+      button.textContent = originalText;
+    }
   }
-  const blob = await resp.blob();
-  const disposition = resp.headers.get("Content-Disposition") || "";
-  const match = disposition.match(/filename\*=UTF-8''([^;]+)/);
-  const filename = match ? decodeURIComponent(match[1]) : defaultFilename;
-  const blobUrl = URL.createObjectURL(blob);
-  const link = document.createElement("a");
-  link.href = blobUrl;
-  link.download = filename;
-  document.body.appendChild(link);
-  link.click();
-  document.body.removeChild(link);
-  URL.revokeObjectURL(blobUrl);
 }