🐛 fix(external-sql): 修复外部 SQL 文件丢失后标签无法关闭

- 后端读取 SQL 文件失败时返回 file_not_found 结构化错误码
- 前端识别文件被删除或移动的场景，允许用户确认关闭标签
- 保留权限、网络盘异常等非缺失错误的关闭拦截，避免误丢草稿
- 补充前后端测试覆盖缺失文件识别与标签关闭提示
Close #566

frontend/src/utils/sqlFileTabDirty.test.ts

@@ -3,6 +3,8 @@ import { describe, expect, it } from 'vitest';
 import {
   getSQLFileTabPath,
   hasSQLFileTabUnsavedChanges,
+  isSQLFileMissingErrorMessage,
+  isSQLFileMissingReadResult,
   isSQLFileQueryTab,
   normalizeSQLFileReadContent,
 } from './sqlFileTabDirty';
@@ -34,4 +36,24 @@ describe('sqlFileTabDirty', () => {
       query: 'select 2;',
     } as any, 'select 1;')).toBe(true);
   });
+
+  it('detects missing SQL file read failures by structured error code', () => {
+    expect(isSQLFileMissingReadResult({
+      success: false,
+      message: '无法读取文件信息: stat /tmp/missing.sql: no such file or directory',
+      data: { errorCode: 'file_not_found', filePath: '/tmp/missing.sql' },
+    })).toBe(true);
+
+    expect(isSQLFileMissingReadResult({
+      success: false,
+      message: '无法读取文件信息: permission denied',
+      data: { filePath: '/tmp/report.sql' },
+    })).toBe(false);
+  });
+
+  it('keeps platform-specific missing file messages as a fallback', () => {
+    expect(isSQLFileMissingErrorMessage('GetFileAttributesEx C:\\Users\\me\\missing.sql: The system cannot find the file specified.')).toBe(true);
+    expect(isSQLFileMissingErrorMessage('stat /Users/me/missing.sql: no such file or directory')).toBe(true);
+    expect(isSQLFileMissingErrorMessage('无法读取文件信息: 权限不足')).toBe(false);
+  });
 });

frontend/src/utils/sqlFileTabDirty.ts

@@ -2,6 +2,8 @@ import type { TabData } from '../types';
 
 const toTrimmedString = (value: unknown): string => String(value ?? '').trim();
 
+export const SQL_FILE_NOT_FOUND_ERROR_CODE = 'file_not_found';
+
 export const getSQLFileTabPath = (tab: Pick<TabData, 'type' | 'filePath'> | null | undefined): string => {
   if (!tab || tab.type !== 'query') return '';
   return toTrimmedString(tab.filePath);
@@ -28,3 +30,35 @@ export const hasSQLFileTabUnsavedChanges = (
   if (!isSQLFileQueryTab(tab)) return false;
   return String(tab.query ?? '') !== diskContent;
 };
+
+const SQL_FILE_MISSING_MESSAGE_PATTERNS = [
+  'no such file or directory',
+  'cannot find the file specified',
+  'system cannot find the file specified',
+  'does not exist',
+  'not exist',
+  '系统找不到指定的文件',
+  '文件不存在',
+];
+
+export const isSQLFileMissingErrorMessage = (message: unknown): boolean => {
+  const normalizedMessage = toTrimmedString(message).toLowerCase();
+  if (!normalizedMessage) return false;
+  return SQL_FILE_MISSING_MESSAGE_PATTERNS.some((pattern) => normalizedMessage.includes(pattern));
+};
+
+export const isSQLFileMissingReadResult = (result: unknown): boolean => {
+  if (!result || typeof result !== 'object') return false;
+  const payload = result as Record<string, unknown>;
+  if (payload.success === true) return false;
+
+  const data = payload.data;
+  if (data && typeof data === 'object') {
+    const errorCode = toTrimmedString((data as Record<string, unknown>).errorCode).toLowerCase();
+    if (errorCode === SQL_FILE_NOT_FOUND_ERROR_CODE) {
+      return true;
+    }
+  }
+
+  return isSQLFileMissingErrorMessage(payload.message);
+};