fix(chat): scope keyboard fallback to Xiaomi Facebook IAB

src/hooks/use-keyboard-height.ts

@@ -2,17 +2,17 @@
 /**
  * 软键盘避让 hook。
  *
- * 目标环境：Facebook IAB / 小米 WebView 等软键盘覆盖页面但 viewport 信号不稳定的浏览器。
+ * 目标环境：小米系设备上的 Facebook IAB 等软键盘覆盖页面但 viewport 信号不稳定的浏览器。
  *
  * 策略：
  *   1. 持续写入 --app-viewport-height，聊天页高度不再只依赖 100dvh。
  *   2. 优先使用 visualViewport 计算键盘高度。
  *   3. 输入框聚焦后测量目标元素是否越过可见底部，计算额外抬升。
- *   4. Android 应用内浏览器若 viewport 未可靠变化，启用保守 fallback 抬升。
+ *   4. 小米系 Android + Facebook IAB 若 viewport 未可靠变化，启用保守 fallback 抬升。
  */
 import { type RefObject, useEffect, useRef } from "react";
 
-import { BrowserDetector, Logger } from "@/utils";
+import { BrowserDetector, Logger, PlatformDetector } from "@/utils";
 
 const KEYBOARD_VAR = "--keyboard-height";
 const VIEWPORT_VAR = "--app-viewport-height";
@@ -57,11 +57,12 @@ export function useKeyboardHeight({
       const metrics = readViewportMetrics();
       const keyboardHeight = Math.round(metrics.keyboardHeight);
       const viewportHeight = Math.round(metrics.visibleHeight);
+      const fallbackLift = computeFallbackLift(metrics);
       const inputLift = Math.round(
         activeRef.current
           ? Math.max(
               computeTargetOverlap(targetRef?.current, metrics.visibleBottom),
-              computeFallbackLift(metrics),
+              fallbackLift,
             )
           : 0,
       );
@@ -93,6 +94,7 @@ export function useKeyboardHeight({
           keyboardHeight,
           viewportHeight,
           inputLift,
+          fallbackLift,
           visualViewport: metrics.hasVisualViewport,
         });
       }
@@ -198,7 +200,11 @@ function computeFallbackLift(metrics: ViewportMetrics): number {
 function shouldUseInAppKeyboardFallback(): boolean {
   if (typeof navigator === "undefined") return false;
   const ua = navigator.userAgent;
-  return /Android/i.test(ua) && BrowserDetector.isInAppBrowser(ua);
+  return (
+    PlatformDetector.isAndroid(ua) &&
+    PlatformDetector.isXiaomiFamilyDevice(ua) &&
+    BrowserDetector.isFacebookInAppBrowser(ua)
+  );
 }
 
 function clamp(value: number, min: number, max: number): number {

src/utils/platform-detect.ts

@@ -85,6 +85,12 @@ export class PlatformDetector {
     return PlatformDetector.getPlatformInfo(ua).isDesktop;
   }
 
+  static isXiaomiFamilyDevice(ua: string | null = null): boolean {
+    const info = PlatformDetector.getPlatformInfo(ua);
+    const target = `${info.deviceVendor} ${info.deviceModel} ${info.userAgent}`;
+    return /\b(Xiaomi|Redmi|POCO|Mi\s|MIX|MIUI)\b/i.test(target);
+  }
+
   private static getUserAgent(ua: string | null = null): string {
     if (ua) return ua;
     if (typeof navigator === "undefined") return "";