fix: attachment download - remote opens in new tab (sync, no CORS fetch), local downloads get toast feedback

app/src/components/common/AttachmentPreview.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useState } from 'react';
 import { Download, Loader2 } from 'lucide-react';
-import { Button, Dialog } from '@/components/ui';
+import { Button, Dialog, useToast } from '@/components/ui';
 import { readFull } from '@/lib/att-cache';
 import type { Attachment } from '@/lib/types';
 
@@ -38,6 +38,7 @@ const KIND_LABEL: Record<AttKind, string> = {
 };
 
 export function AttachmentPreview({ att, onClose }: { att: Attachment | null; onClose: () => void }) {
+  const toast = useToast();
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState('');
   const [content, setContent] = useState<{ kind: AttKind; objectUrl?: string; html?: string; text?: string } | null>(null);
@@ -107,7 +108,28 @@ export function AttachmentPreview({ att, onClose }: { att: Attachment | null; on
       title={(att ? '附件预览 · ' + att.file_name : '附件预览') + (att ? '（' + KIND_LABEL[kind] + '）' : '')}
       footer={att ? (
         <>
-          <Button variant="secondary" className="mr-auto" onClick={() => { void readFull(att).then(r => forceDownload(att.file_name, att.mime ?? undefined, r.data_b64)); }}>
+          <Button variant="secondary" className="mr-auto" onClick={() => {
+            // 远程附件：同步新标签打开（用户手势内触发，不会被拦截；右键即可另存）
+            if (att.remote_url) {
+              const a = document.createElement('a');
+              a.href = att.remote_url;
+              a.target = '_blank';
+              a.rel = 'noopener';
+              a.click();
+              toast('success', '已在新的标签页打开，右键图片可「另存为」');
+              return;
+            }
+            // 本地附件：base64 下载，失败给出提示
+            void (async () => {
+              try {
+                toast('success', '已开始下载');
+                const r = await readFull(att);
+                forceDownload(att.file_name, att.mime ?? undefined, r.data_b64);
+              } catch (e) {
+                toast('error', '下载失败：' + (e as Error).message);
+              }
+            })();
+          }}>
             <Download size={13} /> 下载
           </Button>
           <Button variant="primary" onClick={onClose}>关闭</Button>