UI freezes completely when Bash tool blocks on named pipes (FIFO) - unrecoverable without external kill

Description

Claude Code UI becomes completely unresponsive when a Bash command blocks on reading from a named pipe (FIFO). The UI freezes entirely - no scrolling, no cancel button works, nothing responds until the blocking process is manually killed from another terminal.

Environment

• Claude Code version: 2.0.76
• OS: Linux 6.8.0-59-generic (Ubuntu)
• Shell: Bash

Steps to Reproduce

1. Create a named pipe: mkfifo /tmp/test_pipe
2. In Claude Code, ask it to read from the pipe: "read /tmp/test_pipe" or "show me what's in /tmp/test_pipe"
3. Claude executes cat /tmp/test_pipe or similar
4. Result: Entire UI freezes indefinitely

Expected Behavior

• Bash commands should have a reasonable default timeout
• UI should remain responsive during command execution
• Cancel/interrupt functionality should work
• Or at minimum: warning when attempting to read from FIFO devices

Actual Behavior

• UI completely freezes (no scrolling, no input, no cancel)
• Only way to recover is to kill the blocking process from another terminal
• Child bash process becomes zombie - parent Claude never reaps it
• The FIFO file descriptor stays open on the Claude process

Verified Technical Details

Frozen session still running:

samurax  5872  6.6  1.7 74849296 507376 ?  Sl  11:09  2:05 claude

FIFO still held open by frozen Claude:

claude  5872 samurax  25r  FIFO  259,2  0t0  18481334  /inkode/ports/PESA

Child bash is zombie (never reaped):

samurax  7602  0.0  0.0  0  0 ?  Zs  11:13  0:00 [bash] <defunct>

Process tree showing zombie child:

claude(5872)-+-bash(7602)  # <-- zombie
             |-{claude}(5901)
             |-{claude}(5902)
             ...

Workaround

Use explicit timeouts when reading from pipes:

timeout 1 cat /path/to/pipe

Impact

• High - Complete loss of session control
• Cannot save work or gracefully exit
• Requires external intervention to recover
• Zombie processes accumulate
• First observed on 2.0.76 (Dec 25, 2024)

Suggestions

1. Run Bash commands with a configurable default timeout
2. Keep UI event loop separate from command execution
3. Add non-blocking I/O or polling for command output
4. Detect FIFO/device special files before reading
5. Ensure proper child process reaping (wait/waitpid)