🐛 fix(connection): 修复失败连接高频重试并暂停后台自动元数据拉取 #331

- 后端为失败数据库连接增加冷却窗口，避免短时间内重复真实建连
- 补充失败冷却回归测试，覆盖重复失败、冷却后重试和成功后清理场景
- 前端在后台态暂停查询页、侧边栏和表概览的自动元数据拉取
- 保持手动刷新、手动展开等显式操作行为不变

frontend/src/utils/autoFetchVisibility.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from 'vitest';
+
+import { isAutoFetchVisible } from './autoFetchVisibility';
+
+describe('isAutoFetchVisible', () => {
+  it('allows auto fetch only when the document is visible and not hidden', () => {
+    expect(isAutoFetchVisible({ hidden: false, visibilityState: 'visible' })).toBe(true);
+  });
+
+  it('blocks auto fetch when the page is hidden even if visibilityState looks visible', () => {
+    expect(isAutoFetchVisible({ hidden: true, visibilityState: 'visible' })).toBe(false);
+  });
+
+  it('blocks auto fetch when visibilityState is not visible', () => {
+    expect(isAutoFetchVisible({ hidden: false, visibilityState: 'hidden' })).toBe(false);
+  });
+
+  it('defaults to allowing auto fetch when document visibility APIs are unavailable', () => {
+    expect(isAutoFetchVisible(undefined)).toBe(true);
+    expect(isAutoFetchVisible({})).toBe(true);
+  });
+});

frontend/src/utils/autoFetchVisibility.ts

@@ -0,0 +1,54 @@
+import { useEffect, useState } from 'react';
+
+type AutoFetchVisibilitySource = Partial<Pick<Document, 'hidden' | 'visibilityState'>> | undefined;
+
+export const isAutoFetchVisible = (source?: AutoFetchVisibilitySource): boolean => {
+  if (!source) {
+    return true;
+  }
+
+  if (source.hidden === true) {
+    return false;
+  }
+
+  if (source.visibilityState && source.visibilityState !== 'visible') {
+    return false;
+  }
+
+  return true;
+};
+
+const getDocumentAutoFetchVisibility = (): boolean => {
+  if (typeof document === 'undefined') {
+    return true;
+  }
+
+  return isAutoFetchVisible(document);
+};
+
+export const useAutoFetchVisibility = (): boolean => {
+  const [isVisible, setIsVisible] = useState<boolean>(() => getDocumentAutoFetchVisibility());
+
+  useEffect(() => {
+    if (typeof document === 'undefined') {
+      return undefined;
+    }
+
+    const syncVisibility = () => {
+      setIsVisible(getDocumentAutoFetchVisibility());
+    };
+
+    syncVisibility();
+    document.addEventListener('visibilitychange', syncVisibility);
+    window.addEventListener('focus', syncVisibility);
+    window.addEventListener('pageshow', syncVisibility);
+
+    return () => {
+      document.removeEventListener('visibilitychange', syncVisibility);
+      window.removeEventListener('focus', syncVisibility);
+      window.removeEventListener('pageshow', syncVisibility);
+    };
+  }, []);
+
+  return isVisible;
+};