CLI hangs at 99% CPU on startup with large session .jsonl files

Bug Description

Claude Code CLI hangs indefinitely at 99% CPU usage on startup when the project has large session .jsonl files in ~/.claude/projects/<project-path>/.

Environment

• Claude Code version: 2.1.27
• OS: Ubuntu 24.04 LTS (kernel 6.8.0)
• Hardware: 8 cores, 24GB RAM
• Node.js: v24.13.0

Steps to Reproduce

1. Have a project with accumulated session files totaling ~19MB (one file was 11MB, another 4.7MB)
2. Run claude or claude --print "hello" from the project directory
3. The process immediately spikes to 99% CPU and never responds

Expected Behavior

Claude Code should start normally, possibly with a slight delay for large sessions, or gracefully skip/truncate oversized session files.

Actual Behavior

• The claude process enters an infinite CPU loop at 99%
• No output is produced (not even a prompt)
• The process never recovers — requires kill -9
• Happens consistently on every launch from the affected project directory

Isolation Testing Performed

Systematically tested by removing components one at a time:

| Test | Result |
|------|--------|
| Empty directory (/tmp/claude-test) | ✅ Works |
| Parent directory (~/Development) | ✅ Works |
| Project dir without plugins | ❌ Hangs |
| Project dir without MCP servers | ❌ Hangs |
| Project dir without .git | ❌ Hangs |
| Project dir without node_modules (77k files) | ❌ Hangs |
| Project dir without CLAUDE.md | ❌ Hangs |
| Project dir without session .jsonl files | ✅ Works |

Root cause: Removing all .jsonl session files from ~/.claude/projects/<project-path>/ immediately resolves the issue.

Workaround

rm ~/.claude/projects/<project-path>/*.jsonl
rm -rf ~/.claude/projects/<project-path>/<session-uuid>

Suggestion

• Add a timeout or size limit for session file loading on startup
• Gracefully handle corrupted or oversized session files instead of entering a CPU loop