fix: decouple AI completion from history save failures and improve history API errors

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/history/server-store.ts

@@ -15,6 +15,24 @@ function getDataDir(): string {
   return path.join(process.cwd(), "data", "history");
 }
 
+export function historyStoreErrorMessage(err: unknown): string {
+  if (!(err instanceof Error)) {
+    return "保存测算历史失败";
+  }
+  const code = (err as NodeJS.ErrnoException).code;
+  const dir = getDataDir();
+  if (code === "EACCES" || code === "EPERM") {
+    return `测算历史目录无写入权限（${dir}），请检查 HISTORY_DATA_DIR 或目录权限`;
+  }
+  if (code === "ENOENT") {
+    return `测算历史目录不存在（${dir}），请创建目录或配置 HISTORY_DATA_DIR`;
+  }
+  if (code === "ENOSPC") {
+    return "磁盘空间不足，无法保存测算历史";
+  }
+  return `保存测算历史失败：${err.message}`;
+}
+
 function sanitizeUsername(username: string): string {
   const safe = username.replace(/[^a-zA-Z0-9_-]/g, "_");
   return safe || "guest";