🐛 fix(window): 修复 Windows 恢复焦点后界面缩放异常

Fixes #315

frontend/src/utils/windowsScaleFix.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, it } from 'vitest';
+import {
+  computeWindowsViewportScaleRatio,
+  getWindowsScaleFixNudgedWidth,
+  hasWindowsViewportScaleDrift,
+} from './windowsScaleFix';
+
+describe('windowsScaleFix', () => {
+  it('treats matching window and viewport metrics as stable', () => {
+    const ratio = computeWindowsViewportScaleRatio({
+      windowWidth: 1920,
+      innerWidth: 1280,
+      devicePixelRatio: 1.5,
+    });
+
+    expect(ratio).toBeCloseTo(1, 5);
+    expect(hasWindowsViewportScaleDrift({
+      windowWidth: 1920,
+      innerWidth: 1280,
+      devicePixelRatio: 1.5,
+    })).toBe(false);
+  });
+
+  it('detects zoom drift from viewport width mismatch', () => {
+    expect(hasWindowsViewportScaleDrift({
+      windowWidth: 1920,
+      innerWidth: 1100,
+      devicePixelRatio: 1.5,
+    })).toBe(true);
+  });
+
+  it('detects zoom drift from visual viewport scale', () => {
+    expect(hasWindowsViewportScaleDrift({
+      windowWidth: 1600,
+      innerWidth: 1600,
+      devicePixelRatio: 1,
+      visualViewportScale: 1.12,
+    })).toBe(true);
+  });
+
+  it('returns a one-pixel nudge width for normal windows', () => {
+    expect(getWindowsScaleFixNudgedWidth(960)).toBe(959);
+    expect(getWindowsScaleFixNudgedWidth(420)).toBe(421);
+  });
+});