Stop hook timeout does not kill child process tree

Bug description

When a Stop hook spawns a child process (e.g., Start-Process in PowerShell), Claude Code waits for the entire process tree to finish, ignoring the configured timeout value.

Reproduction steps

1. Configure a Stop hook in ~/.claude/settings.json:

{
  "hooks": {
    "Stop": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "powershell -ExecutionPolicy Bypass -File \"some-script.ps1\"",
            "timeout": 15
          }
        ]
      }
    ]
  }
}

1. The script spawns a child process (e.g., calling claude -p --model haiku for session summarization):

Start-Process -FilePath "powershell" -ArgumentList $args -NoNewWindow

1. End a Claude Code session (Ctrl+C or /exit)

Expected behavior

Claude Code should respect the timeout value (15s in this case), kill the hook process and its children, then exit cleanly.

Actual behavior

Claude Code hangs for 15+ minutes after the session ends, waiting for the child process (claude -p --model haiku) to complete. The timeout appears to have no effect on the child process tree.

Workaround

Use -WindowStyle Hidden instead of -NoNewWindow in the hook script to detach child processes from the parent's process tree. This way the hook script exits immediately and Claude Code doesn't wait.

Environment

• OS: Windows 11
• Shell: PowerShell
• Claude Code: latest (as of Feb 2026)