[BUG] Claude Code freezes with memory leak when processing output with extremely long lines (minified files)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

Related Issue

This is related to but distinct from #17394 (Session Freeze on Large File Read Error). That issue was about file size exceeding 256KB. This issue is about line length regardless of file size.

Description

Claude Code freezes with 100%+ CPU and memory leak (~30MB/sec) when processing files or command output containing extremely long lines, such as minified JSON, JS, CSS, SVG, or XML.

Steps to Reproduce

# Create a minified file (few lines, very long)
cd /tmp && mkdir test-line-length && cd test-line-length
python3 -c "print('x' * 600000)" > minified.txt
wc -l minified.txt  # Shows: 1 line
ls -lh minified.txt  # Shows: ~600KB

claude
# Ask: "read minified.txt"

What happens

1. Read tool fails with "exceeds maximum size" error
2. Claude falls back to head -100 minified.txt
3. Since file has only 1 line, head returns the entire 600KB line
4. Claude freezes in "Baking..." state
5. CPU spikes to 140%+, memory leaks at ~30MB/sec
6. Terminal unresponsive, Ctrl+C ignored

Root Cause

The issue is line count ≠ byte count. Commands like head -N limit by lines, not bytes. A minified file can have millions of characters on a single line.

Real-world example

- File size: 2.9MB
- Line count: 5
- Average line length: ~580KB

head -100 would return nearly the entire file.

Diagnostic data (from strace)

futex(..., FUTEX_WAIT_PRIVATE, ...) = -1 EAGAIN (spinning)
mmap(...) allocating new memory repeatedly

Process state: No TCP connections (not waiting on API), pure CPU spin loop.

Environment

• Claude Code: v2.1.12
• Platform: Linux (Fedora)
• Terminal: Standard

Expected behavior

• Detect long lines before processing
• Truncate by bytes, not just lines
• Fail gracefully without freezing