diff --git a/src/hooks/use-keyboard-height/__tests__/environment.test.ts b/src/hooks/use-keyboard-height/__tests__/environment.test.ts
new file mode 100644
index 00000000..5e28b450
--- /dev/null
+++ b/src/hooks/use-keyboard-height/__tests__/environment.test.ts
@@ -0,0 +1,73 @@
+import { describe, expect, it } from "vitest";
+
+import { shouldEnableKeyboardAdaptation } from "../environment";
+import type { KeyboardAdaptEnvironment } from "../types";
+
+function makeEnvironment(
+  overrides: Partial<KeyboardAdaptEnvironment> = {},
+): KeyboardAdaptEnvironment {
+  return {
+    platform: "android",
+    osName: "Android",
+    osVersion: "16",
+    deviceVendor: "Xiaomi",
+    deviceModel: "2211133C",
+    isAndroid: true,
+    isIOS: false,
+    isMobile: true,
+    browserName: "Facebook",
+    browserVersion: "566.0.0.48.73",
+    isInAppBrowser: true,
+    inAppBrowserName: "facebook",
+    isXiaomiFamilyDevice: true,
+    isFacebookInAppBrowser: true,
+    hasVisualViewport: true,
+    hasVirtualKeyboard: true,
+    usesXiaomiFacebookFallback: true,
+    ...overrides,
+  };
+}
+
+describe("shouldEnableKeyboardAdaptation", () => {
+  it("enables only for Xiaomi Android Facebook in-app browser fallback", () => {
+    expect(shouldEnableKeyboardAdaptation(makeEnvironment())).toBe(true);
+
+    expect(
+      shouldEnableKeyboardAdaptation(
+        makeEnvironment({
+          platform: "ios",
+          osName: "iOS",
+          osVersion: "18",
+          deviceVendor: "Apple",
+          deviceModel: "iPhone",
+          isAndroid: false,
+          isIOS: true,
+          isXiaomiFamilyDevice: false,
+          usesXiaomiFacebookFallback: false,
+        }),
+      ),
+    ).toBe(false);
+
+    expect(
+      shouldEnableKeyboardAdaptation(
+        makeEnvironment({
+          browserName: "Instagram",
+          inAppBrowserName: "instagram",
+          isFacebookInAppBrowser: false,
+          usesXiaomiFacebookFallback: false,
+        }),
+      ),
+    ).toBe(false);
+
+    expect(
+      shouldEnableKeyboardAdaptation(
+        makeEnvironment({
+          deviceVendor: "Samsung",
+          deviceModel: "SM-G991B",
+          isXiaomiFamilyDevice: false,
+          usesXiaomiFacebookFallback: false,
+        }),
+      ),
+    ).toBe(false);
+  });
+});
diff --git a/src/hooks/use-keyboard-height/environment.ts b/src/hooks/use-keyboard-height/environment.ts
index c16277ae..0b2d3736 100644
--- a/src/hooks/use-keyboard-height/environment.ts
+++ b/src/hooks/use-keyboard-height/environment.ts
@@ -37,10 +37,11 @@ export function getKeyboardAdaptEnvironment(
 export function shouldEnableKeyboardAdaptation(
   environment: KeyboardAdaptEnvironment,
 ): boolean {
-  return environment.isInAppBrowser;
+  return environment.usesXiaomiFacebookFallback;
 }
 
 export function shouldUseInAppKeyboardFallback(): boolean {
   if (typeof navigator === "undefined") return false;
-  return getKeyboardAdaptEnvironment(navigator.userAgent).usesXiaomiFacebookFallback;
+  return getKeyboardAdaptEnvironment(navigator.userAgent)
+    .usesXiaomiFacebookFallback;
 }
diff --git a/src/hooks/use-keyboard-height/index.ts b/src/hooks/use-keyboard-height/index.ts
index 256d9f95..922e4d1e 100644
--- a/src/hooks/use-keyboard-height/index.ts
+++ b/src/hooks/use-keyboard-height/index.ts
@@ -2,7 +2,7 @@
 /**
  * 软键盘避让 hook。
  *
- * 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。
+ * 目标环境：小米系 Android 设备上的 Facebook IAB。
  *
  * 策略：
  *   1. 持续写入 --app-viewport-height，聊天页高度不再只依赖 100dvh。
@@ -87,7 +87,7 @@ export function useKeyboardHeight({
     if (!shouldEnableKeyboardAdaptation(environment)) {
       resetKeyboardVars();
       log.debug("[keyboard] disabled", {
-        reason: "regular-browser",
+        reason: "not-xiaomi-facebook-iab",
         environment,
       });
       return;