100% CPU freeze on any input in large project directory (macOS 26.3)

Environment

• Claude Code: 2.1.27
• macOS: 26.3 (Tahoe beta, build 25D5087f)
• Node: v20.19.6

Symptom

Claude Code instantly freezes at 100% CPU on any input (even pwd) when launched in a specific large project directory. The process enters R (running/spinning) state and does not respond to SIGTERM - requires kill -9 to terminate.

Directory characteristics

• 173,844 files
• 12GB total size
• Has .claudeignore excluding data/, node_modules/, .venv/, etc.

Attempted fixes (none worked)

• Disabled all plugins (enabledPlugins: {})
• Disabled all MCP servers (mcpServers: {})
• Removed all hooks (PostToolUse, Stop, etc.)
• Removed hookify plugin and cleared its cache
• Updated .claudeignore with comprehensive exclusions
• Launched with --no-config flag

Observations

• Same user, same machine works fine in smaller directories
• Multiple Claude instances can freeze simultaneously
• Freeze happens immediately on first input, before any tool use
• Process state shows R+ (running, foreground) instead of S+ (sleeping)

Reproduction

1. Have a large project directory (100k+ files)
2. Launch claude in that directory
3. Type any input (e.g., pwd)
4. Process freezes at 100% CPU

Workaround

Working in smaller directories works fine. Issue is specific to large project directories.