Claude Desktop leaks pty (ptmx) fds -> system-wide pty exhaustion (terminals die with 'forkpty: Device not configured')

Environment

• Claude Desktop: 1.11187.4
• claude-code: 2.1.165
• macOS: 26.3 (25D125), Mac16,7 (Apple Silicon)

Summary

The Claude Desktop main process (/Applications/Claude.app/Contents/MacOS/Claude) accumulates pty master file descriptors (/dev/ptmx) without releasing them. Over a ~2-hour session it leaked to 509 open ptmx handles, hitting the macOS limit kern.tty.ptmx_max=511. Once exhausted, no application on the machine can allocate a new pty — every terminal (Terminal.app, iTerm2) fails to start a shell and the window closes instantly; tmux/script also fail.

Evidence

$ lsof -n /dev/ptmx | awk 'NR>1{print $2}' | sort | uniq -c | sort -rn
 509 4065     # /Applications/Claude.app/Contents/MacOS/Claude  (single main process)
   1 16467    # VS Code

$ sysctl kern.tty.ptmx_max
kern.tty.ptmx_max: 511

$ python3 -c "import pty; pty.openpty()"
OSError: out of pty devices

# Terminal.app window content right before it closes:
[forkpty: Device not configured]

All 509 handles are held by the single main process (pid 4065), not spread across child session processes — killing individual claude-code subprocesses does not free them; only quitting the main app does. This points to a leak in the parent process's pty management, not per-session cleanup.

Reproduction

1. Run Claude Desktop with Claude Code executing shell/Bash tools over a long session (multiple sessions / agents).
2. Each tool invocation opens a pty whose master fd is never closed after the child exits.
3. Leaked ptmx handles climb to the ptmx_max ceiling (511) over a few hours.
4. Open Terminal.app / iTerm2 -> window opens then closes instantly (forkpty fails).

Impact

System-wide: all terminals on the machine become unusable, not just Claude's. The symptom is highly misleading — it looks like a zsh/tmux startup crash, which makes it very hard to diagnose.

Workaround

• Temporary: sudo sysctl -w kern.tty.ptmx_max=999 (raises the ceiling above the leak; lost on reboot; 999 is the macOS hard cap).
• Real recovery: fully quit & relaunch Claude Desktop to release all leaked handles.

Expected

pty master fds should be closed when the corresponding tool invocation / child process ends.