[BUG] Process spins at 100% CPU after terminal disconnect (macOS)

Description

After a terminal disconnects (e.g., closing terminal window, laptop sleep), Claude Code keeps running at 100% CPU indefinitely instead of exiting gracefully. The process consumed 30+ hours of CPU time over ~2 days before I noticed and killed it.

Note: The process was NOT consuming API tokens - it appeared to be stuck in a local busy loop, not making API calls. The conversation had completed successfully before the terminal was closed.

Note: This was observed once and is not reproducible on demand. Filing for awareness in case others encounter the same issue.

Reproduction

1. Start a Claude Code session in a terminal
2. Complete a task (conversation ends naturally)
3. Close the terminal window (or disconnect via sleep/SSH drop)
4. Process continues running, spinning at 100% CPU

Evidence

$ ps aux | grep claude
mycrobe  92827 101.9  0.9 445612048 289376   ??  R    Fri12PM 1804:13.31 claude

$ lsof -p 92827 | head -20
COMMAND   PID     USER   FD      TYPE   ...  NAME
node    92827 mycrobe  cwd       DIR   ...  /Users/mycrobe/tmp
node    92827 mycrobe    0            (revoked)
node    92827 mycrobe    1            (revoked)
node    92827 mycrobe    2            (revoked)

• stdin/stdout/stderr are "revoked" (terminal gone)
• Process is in R (running) state, not sleeping
• Regular kill didn't work, required kill -9

Environment

• Claude Code Version: 2.1.2
• OS: macOS Darwin 24.6.0 (Sequoia)
• Node.js Version: v20.19.4
• Node Path: /opt/n/bin/node (via n version manager)
• Terminal: iTerm2 (window was closed)

Expected Behavior

When the terminal disconnects (SIGHUP or revoked FDs), Claude Code should detect this and exit cleanly.

Related Issues

• #11339 - 100% CPU in interactive mode (similar symptom, different trigger)
• #8570 - Process behavior on disconnect (process pauses vs spins)
• #11707 - Windows node.exe hangs after terminal close