Mos 4.2.1 duplicates every physical keyboard key press system-wide on macOS 26.5.2

[BFlameSwift]

Summary | 摘要

When Mos 4.2.1 is running, a single press on the MacBook's built-in physical keyboard produces two identical characters system-wide. For example, pressing j once outputs jj.

Mos 4.2.1 运行时，MacBook 内置物理键盘单次按键会在系统范围内产生两个相同字符，例如只按一次 j 会输出 jj。

The behavior is independent of the selected input method. Quitting Mos immediately restores normal one-character-per-key behavior. Reopening Mos makes the duplicate input return. Removing the previous app and reinstalling Mos with the official Homebrew cask did not fix it.

该问题与当前输入法无关。退出 Mos 后立即恢复为一次按键输出一个字符；重新启动 Mos 后重复输入再次出现。删除原应用并通过官方 Homebrew cask 重新安装后问题仍然存在。

Steps to Reproduce | 如何重现

1. Launch Mos 4.2.1 with Accessibility permission granted.

2. Open any text field (TextEdit, browser, chat application, etc.).

3. Press a key once on the built-in MacBook keyboard, for example j.

4. Observe that jj is entered.

5. Quit Mos and press the same key once again.

6. Observe that only one j is entered.

7. Relaunch Mos; duplicate input returns.

8. 启动已获得辅助功能权限的 Mos 4.2.1。

9. 打开任意文本输入框。

10. 在 MacBook 内置键盘上轻按一次按键，例如 j。

11. 实际输入为 jj。

12. 退出 Mos，再按一次同一按键。

13. 输入恢复为单个 j。

14. 重新启动 Mos，重复输入再次出现。

Expected Behavior | 期望结果

Mos should not alter ordinary physical keyboard input. One physical key press should produce one character.

Mos 不应修改普通物理键盘输入；一次物理按键应只产生一个字符。

Actual Behavior | 实际结果

Every ordinary key press is processed twice while Mos is running. The issue affects the whole system and multiple input methods.

Mos 运行时，普通按键会被处理两次。问题影响整个系统，并且在不同输入法下均可复现。

Environment | 环境信息

• Mos version | Mos 版本: 4.2.1, build 20260531.1
• Installation | 安装方式: brew install --cask mos
• macOS version | macOS 版本: 26.5.2 (25F84)
• Mac model / chip | 机型 / 芯片: MacBook Pro (Mac14,9), Apple M2 Pro, 16 GB
• Keyboard | 键盘: Built-in Apple Internal Keyboard / Trackpad
• Mouse / trackpad model | 鼠标 / 触控板型号: Logitech MX Anywhere 3; built-in trackpad
• Connection type | 连接方式: Bluetooth / built-in
• Affected application | 受影响应用: Whole system
• Accessibility permission granted | 是否已授予辅助功能权限: Yes
• Input methods tested | 已测试输入法: ABC, Doubao IME, WeType
• Other input, mouse, keyboard, or window-management tools | 其他工具: Raycast Beta, uTools, Logi Options+, Mac Mouse Fix, Universal Control, UU Remote, and Codex Computer Use were isolated through controlled process-group ablation.

Mos Settings Involved | 涉及的 Mos 设置

No single Mos option has been isolated yet. The problem occurs when Mos is running and disappears when the Mos process is stopped.

尚未定位到某个具体 Mos 选项。现阶段确认：Mos 进程运行时问题出现，Mos 进程停止后问题消失。

Logs, Screenshots, or Recordings | 日志、截图或录屏

No recording is attached yet. Process-level ablation was used to isolate the cause:

1. Candidate input-hook processes were divided into two groups.
2. Disabling the non-Mos group did not fix duplicate typing.
3. Disabling the group containing Raycast Beta and Mos fixed it.
4. Re-enabling that group reproduced the problem.
5. Keeping Raycast Beta running but quitting only Mos fixed it.
6. Reinstalling Mos 4.2.1 from the official Homebrew cask and relaunching it reproduced the problem again.

暂未附录屏。已通过进程级二分消融定位：

1. 将可能处理输入事件的进程分为两组。
2. 关闭不包含 Mos 的一组后问题仍存在。
3. 关闭包含 Raycast Beta 和 Mos 的一组后恢复正常。
4. 重新开启该组后问题再次出现。
5. 保持 Raycast Beta 运行、只退出 Mos 后恢复正常。
6. 通过官方 Homebrew cask 重新安装 Mos 4.2.1 并启动后，问题仍然复现。

Duplicate Check | 重复 issue 检查

Searched open and closed issues for keyboard, duplicate input, double input, key press twice, keyboard repeat, 按键重复, 重复输入, and 键盘.

Related but different reports:

• mos与Logi options+同时使用时发生冲突 #498: Logi Options+ and Mos combine scroll distance.
• mos启动状态关闭系统隐私权限，导致鼠标、键盘无法正常操作 #903: mouse/keyboard become unusable after revoking Mos privacy permission.
• Problem with my Logitech MX Mechanical Keyboard for Mac #948: Logitech keyboard backlight remains on while Mos runs.
• Keyboard Maestro Conflicts #175 / 与 Keyboard Maestro 的兼容问题 #120: Keyboard Maestro affects Mos modifier-key state.
• 侧键冲突:绑定的操作与侧键默认的操作同时执行 #830: mouse side-button default and assigned actions both execute.

None describes every built-in keyboard key press producing two characters.

Additional Context | 额外说明

The previous Mos app bundle was removed, then Mos was installed and registered through the official Homebrew cask:

mos 4.2.1,20260531.1
/opt/homebrew/Caskroom/mos/4.2.1,20260531.1

Code-signing verification and Gatekeeper assessment both passed. User preferences were preserved during reinstall (--zap was not used), so a preference-related trigger remains possible.