[BUG] Claude Code crashes with PAC trap (EXC_BREAKPOINT) when opening large monorepo on macOS 26

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

What's Wrong?

Claude Code crashes within ~2-5 seconds of opening in a large monorepo root directory. The crash is a pointer authentication trap (PAC) in the Bun runtime's worker pool threads.

The crash occurs consistently when launching claude from the monorepo root, but works fine when launching from subdirectories of the same repo.

What Should Happen?

Claude Code should start successfully regardless of the directory size.

Error Messages/Logs

From the crash report (~/Library/Logs/DiagnosticReports/claude-*.ips):

"exception" : {"codes":"0x0000000000000001, 0x0000000104328178","rawCodes":[1,4365386104],"type":"EXC_BREAKPOINT","signal":"SIGTRAP"}
"termination" : {"flags":0,"code":5,"namespace":"SIGNAL","indicator":"Trace/BPT trap: 5","byProc":"exc handler"}
"faultingThread" : 33
"legacyInfo" : { "threadTriggered" : { "name" : "Bun Pool 7" } }

ESR description: "(Breakpoint) pointer authentication trap IB"

Steps to Reproduce

1. Have a large monorepo (Rails + Node.js, ~70 top-level directories, 1GB .git, large node_modules)
2. Run cd /path/to/large-monorepo && claude
3. Claude Code opens briefly then crashes within 2-5 seconds
4. Crash report is generated in ~/Library/Logs/DiagnosticReports/

Workaround: Opening Claude from a subdirectory works fine:

cd /path/to/large-monorepo/apps/subproject && claude  # Works
cd /path/to/large-monorepo && claude                   # Crashes

Troubleshooting attempted (none fixed the issue):

• Clearing project cache (rm -rf ~/.claude/projects/-Users-*-src-intercom)
• Disabling plugins (CLAUDE_CODE_DISABLE_PLUGINS=1 claude)
• Removing .claude directory from the repo
• No broken symlinks found

Claude Model

Opus

Is this a regression?

I don't know

Claude Code Version

2.1.15

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

• macOS version: 26.2 (25C56) - Apple Silicon (ARM64)
• The crash is in "Bun Pool" worker threads, suggesting it happens during async initialization
• Multiple crash reports generated over short period indicate consistent reproduction
• System has plenty of resources (48GB RAM, 63% CPU idle at time of crash)
• File descriptor limits are unlimited

The PAC (Pointer Authentication Code) trap suggests possible memory corruption or a race condition in the Bun runtime when handling large directory structures on macOS 26.