fix(ssa): harden spreadsheet upload recognition and guidance

Fix SSA data-context generation for Excel uploads by parsing xlsx/xls via extension-aware paths instead of UTF-8 fallback.
Add on-demand overview rebuild in Agent flow, align xls friendly prompts on frontend/backend, and surface backend upload errors to users.

Made-with: Cursor

frontend-v2/src/modules/ssa/components/SSAChatPane.tsx

@@ -137,6 +137,22 @@ export const SSAChatPane: React.FC = () => {
     const file = e.target.files?.[0];
     if (!file) return;
 
+    const ext = file.name.split('.').pop()?.toLowerCase() || '';
+    if (ext === 'xls') {
+      const msg = '系统为了保证表格解析的稳定性，当前仅支持 .xlsx / .csv 格式。请您在本地 Excel/WPS 中打开该文件，选择“另存为 -> Excel 工作簿 (.xlsx)”后再次上传。';
+      setUploadStatus('error');
+      setError(msg);
+      addToast(msg, 'error');
+      return;
+    }
+    if (!['csv', 'xlsx'].includes(ext)) {
+      const msg = `不支持的文件类型: .${ext || 'unknown'}。当前支持：.csv、.xlsx`;
+      setUploadStatus('error');
+      setError(msg);
+      addToast(msg, 'error');
+      return;
+    }
+
     setUploadStatus('uploading');
     setError(null);
 

frontend-v2/src/modules/ssa/hooks/useAnalysis.ts

@@ -91,7 +91,16 @@ export function useAnalysis(): UseAnalysisReturn {
         body: formData,
       });
 
-      if (!response.ok) throw new Error('上传失败');
+      if (!response.ok) {
+        let errMsg = '上传失败';
+        try {
+          const errData = await response.json();
+          errMsg = errData?.error || errData?.message || errMsg;
+        } catch {
+          // ignore parse error
+        }
+        throw new Error(errMsg);
+      }
       const result = await response.json();
       setUploadProgress(100);
       return result;