[BUG] Windows: stopShellPty on tab switch kills session with exit code 4294967295 — regression in May 27+ build

Preflight Checklist

• [x] I have searched existing issues and this is the Windows-specific counterpart of #62559 and #62985
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

On Windows, switching between session tabs in Claude Code Desktop kills the unfocused session's CLI process with exit code 4294967295 (= 0xFFFFFFFF = Windows equivalent of SIGTERM/exit 143 on macOS).

The user-visible error is:

세션이 중단되었습니다 / 메시지를 다시 보내보세요. Claude Code process exited with code 4294967295

This is the same regression as #62559 / #62985 but on Windows. Exit code 143 (SIGTERM) on macOS maps to 4294967295 (0xFFFFFFFF, i.e. -1 as signed 32-bit) on Windows when a process is forcibly terminated.

Log Signature (from %APPDATA%\Claude\logs\main.log)

[CCD] LocalSessions.setFocusedSession: sessionId=null
[CCD] LocalSessions.setFocusedSession: sessionId=local_<session-B>
LocalSessions.stopShellPty: sessionId=local_<session-A>   ← kills active session
[IdleManager:session] Starting idle timeout for local_<session-A>: 900s
Shell PTY for session local_<session-A> exited (stale — already replaced)

Matching the exact pattern described in #62559.

Steps to Reproduce

1. Open two or more local Code sessions in Claude Code Desktop (Windows)
2. Be active in session A
3. Click session B in the sidebar
4. Click back to session A
5. Session A shows "Claude Code process exited with code 4294967295"

What Should Happen?

Switching tabs should not kill the unfocused session's CLI process — it should stay alive in the background (as it did before the May 27 build).

Additional Context

• This causes multiple interruptions per hour during normal multi-session workflows
• ClaudeSessionWatch automation (task scheduler, 5-min polling) partially mitigates by restarting sessions, but there is a 5–10 min gap before recovery
• The 15-minute IdleManager session timeout also kills PTY on inactivity, compounding the issue
• Previously worked fine; regression started with the update received on 2026-05-31 (claude.exe timestamped 16:22 KST, Desktop app 21:36 KST)

Environment

• OS: Windows 11 (10.0.26200), HP laptop, Modern Standby (S0ix)
• Claude Code Desktop: 1.9659.2.0
• claude.exe: 2.1.156
• Platform: claude.ai (OAuth)

Related Issues

• #62559 — macOS counterpart (SIGTERM / exit 143), labeled regression
• #62985 — macOS counterpart, same stopShellPty root cause