v2.1.12: SIGTRAP/PAC crash on Apple Silicon (arm64) during startup

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code v2.1.12 crashes immediately on startup with zsh: trace trap error on Apple Silicon Mac (M3). The crash happens intermittently - sometimes it works after multiple retries.

The crash report shows:

• Exception type: EXC_BREAKPOINT with signal SIGTRAP
• ESR description: (Breakpoint) pointer authentication trap IB
• Faulting thread: "Bun Pool 2" (thread pool worker)

This is a PAC (Pointer Authentication Code) failure in the Bun runtime, where the CPU detects a corrupted/invalid function return address.

What Should Happen?

Claude Code should start normally without crashing.

Error Messages/Logs

zsh: trace trap  claude --dangerously-skip-permissions

Crash report excerpt:
{
  "exception": {"codes":"0x0000000000000001, 0x0000000101dc93b0","rawCodes":[1,4326200240],"type":"EXC_BREAKPOINT","signal":"SIGTRAP"},
  "termination": {"flags":0,"code":5,"namespace":"SIGNAL","indicator":"Trace/BPT trap: 5","byProc":"exc handler","byPid":50965},
  "faultingThread": 19,
  "threads": [...{"triggered":true,"id":10450031,"name":"Bun Pool 2","threadState":{..."esr":{"value":4060136561,"description":"(Breakpoint) pointer authentication trap IB"}...}...}]
}

Steps to Reproduce

1. Install Claude Code v2.1.12 on Apple Silicon Mac (M3)
2. Run claude or claude --dangerously-skip-permissions from terminal
3. Observe immediate crash with zsh: trace trap
4. Retry - sometimes works after 1-3 attempts

Note: The crash happens more frequently when launched from Terminal Spawner (Obsidian plugin) where the process runs under Obsidian's process coalition.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.9

Claude Code Version

2.1.12

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

System Info:

• macOS 15.6 (Build 24G84)
• Mac16,13 (M3 MacBook Air)
• ARM64 native binary (not Rosetta)
• Code signing verified: valid signature from Anthropic (TeamID: Q6L2SF6YDW)

Crash Details:

• 4 crashes occurred within ~35 seconds on 2026-01-20 around 07:12
• All crashes show identical PAC (Pointer Authentication Code) failure
• Crash happens in Bun thread pool worker during startup
• No crashes on v2.1.9 or v2.1.7

Full crash report available in: ~/Library/Logs/DiagnosticReports/2.1.12-2026-01-20-071249.ips