Severe PTY leak in qwen CLI causes tmux split/new-window failures (out of pty devices)

[Essviv]

Bug Description

After running qwen -y for long sessions, the process leaks PTY file descriptors (/dev/ptmx) and eventually exhausts system PTY capacity.
When this happens, tmux can no longer create panes/windows.

Environment

• OS: macOS 15.5 (Darwin 24.5.0)
• Shell: zsh
• tmux: 3.6a
• qwen CLI launched as: qwen -y
• Node runtime observed in process tree

Expected Behavior

qwen -y should not continuously accumulate PTY descriptors.
tmux should continue to split panes/create windows normally.

Actual Behavior

After long-running qwen sessions:

• tmux split-window / tmux new-window fails with:
  • create window failed: fork failed: Device not configured
• Python PTY test fails with:
  • OSError('out of pty devices')

Diagnostics

• Kernel PTY max observed: kern.tty.ptmx_max: 511
• One qwen -y node process held ~444 /dev/ptmx descriptors
• Another qwen -y process held ~50 /dev/ptmx descriptors
• Top PTY holders showed qwen dominating PTY usage
• After killing those qwen processes:
  • PTY allocation worked immediately (openpty ok)
  • tmux pane split worked again

Minimal Reproduction (long-run)

1. Start qwen -y and keep it running with multiple tool/task operations for many hours.
2. Periodically check PTY usage:

   lsof -nP /dev/ptmx | awk 'NR>1{c[$2]++; cmd[$2]=$1} END{for (p in c) printf "%5d %s %s\\n", c[p], p, cmd[p]}' | sort -nr | head

3. Observe qwen process PTY count continuously increasing.
4. Eventually tmux split-window fails with the error above.

Notes

This appears to be a PTY/FD cleanup leak in long-lived qwen sessions.
Please investigate PTY lifecycle management and child process teardown paths.

[Mingholy]

This is kind of tricky. I've tested around multiple attempts but none of them works. I suppose this is related to microsoft/node-pty#882 and cannot be fully resolved on the Qwen-Code side.