Claude.app leaks PTY master fds (/dev/ptmx) — exhausts macOS kern.tty.ptmx_max after long Bash-heavy sessions

Summary

Claude.app (macOS desktop) leaks one open /dev/ptmx master fd per Bash tool invocation. The fds accumulate until macOS PTY limit (kern.tty.ptmx_max = 511) is exhausted, causing all terminal emulators on the system to fail with "cannot allocate any more pty devices".

Environment

• macOS Darwin 25.5.0
• Claude.app (desktop, Electron)
• Ghostty terminal emulator
• kern.tty.ptmx_max = 511 (macOS default)

Reproduction

1. Start a Claude Code session in Claude.app (desktop).
2. Run many Bash tool calls over several hours (e.g., a complex multi-step engineering task with 100+ Bash invocations).
3. Observe: /dev/ttys* accumulates without bound, never shrinks.
4. Eventually, opening a new terminal tab/window fails with: "Your system cannot allocate any more pty devices."

Evidence

After a ~5-hour session with ~500 Bash tool calls:

$ ls /dev/ttys* | wc -l
527

$ lsof -p <Claude.app PID> | grep ptmx | wc -l
510

$ lsof -p <Claude.app PID> | grep ptmx | head -3
Claude  34050 elihu   43u  CHR 15,218  0t0  605 /dev/ptmx
Claude  34050 elihu   73u  CHR 15,229  0t0  605 /dev/ptmx
Claude  34050 elihu   80u  CHR 15,401  0t0  605 /dev/ptmx

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

PTY creation rate correlates 1:1 with Bash tool invocations (verified via stat timestamps on /dev/ttys*).

Root Cause

Each Bash tool call opens a PTY master via /dev/ptmx but the fd is never closed after the child process exits. On macOS, the slave device (/dev/ttysXXX) is not reclaimed until the master fd is released.

Impact

Exhausts system-wide PTY slots. All processes on the machine that need a new terminal (Ghostty, iTerm2, Terminal.app, ssh, tmux) fail until Claude.app is restarted.

Workaround

Restart Claude.app — releases all leaked fds, kernel immediately reclaims the zombie PTY devices.