[BUG] 2.1.143 regression: mouse wheel scrolls input history instead of chat transcript (Windows)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

After upgrading to 2.1.143, scrolling up with the mouse wheel cycles through my prior input history — i.e. it behaves as if I pressed the Up arrow — instead of scrolling the chat transcript / scrollback window.

Downgrading to 2.1.142 fully restores the expected behavior. The regression only occurs on 2.1.143 sessions.

What Should Happen?

Mouse wheel up should scroll the chat transcript (prior assistant/user messages, tool output) upward in the viewport. Cycling input history should remain bound to the Up arrow key only.

Error Messages/Logs

_No error messages — purely a UI input-handling regression._

Steps to Reproduce

1. On Windows 11 with Windows Terminal + PowerShell, install Claude Code 2.1.143.
2. Trigger condition (newly isolated): only background / agent-view sessions are affected. A freshly started foreground claude session does NOT exhibit the regression. To reproduce, do one of:

• Dispatch with claude --bg "<prompt>" then claude attach <id>, or
• Open any regular session, run /bg to background it, then claude agents and attach back to it.

1. Generate a multi-screen transcript (any long response works).
2. Place the cursor anywhere over the terminal and roll the mouse wheel up.
3. Observed: the prompt input field cycles backward through prior user messages (Up-arrow behavior).
4. Expected: the chat transcript scrolls upward in the viewport.
5. Run claude migrate-installer / reinstall 2.1.142 — bug disappears.
6. Reinstall 2.1.143 — bug returns.

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.142

Claude Code Version

2.1.143 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Possibly the same underlying change as #58364 (iTerm2 + tmux on macOS, mouse wheel hijacked to input history on 2.1.138 / 2.1.139). That report is mac-specific and lists 2.1.138 as the first bad version; this Windows reproduction first appears at 2.1.143, suggesting either the same mouse-input handler regression has now reached the Windows TUI path, or a fix on that earlier report did not generalize.

Related: #51393 (cannot scroll up in Windows Terminal — 2.1.x regression).

Update (after further isolation): the regression is confined to the agent-view / background-session code path. Foreground sessions on 2.1.143 do not exhibit the bug at all; only sessions reached via claude attach <id> or after a /bg → claude agents round-trip. This suggests the mouse-input handler is being remapped (or not properly restored) when a session passes through the supervisor-hosted bg path.