[BUG] issues #57053

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?

cowork and code not working, crash error

What Should Happen?

it should work

Error Messages/Logs

## Description

Claude Code / Cowork crashes with `Claude Code process exited with code 3` every time a **new** conversation is started. The bundled Bun runtime segfaults within ~15ms of process start. **Resuming or continuing an existing conversation works fine, every time** — the crash is isolated to the new-conversation code path.

This started today without any changes on my end. It worked fine yesterday; Claude Code auto-updated in the background, and the crash began appearing right after.

## Environment

- OS: Windows 10, build 26200
- Claude Code version: 2.1.219
- Bundled Bun version: 1.4.0
- Architecture: Windows x64 (baseline), CPU features: sse42 avx avx2

## Steps to reproduce

1. Open Claude Code / Cowork desktop app.
2. Start a **new** conversation.
3. Process crashes immediately (~15ms elapsed) with a Bun segmentation fault.
4. Start (or resume) an **existing** conversation instead → works normally, no crash.

## Expected behavior

New conversations should start without crashing, same as resuming existing ones.

## Actual behavior

100% reproducible crash on new-conversation creation. Existing conversations are unaffected, which suggests the fault is in whatever code path runs on first-time session/state-file creation (e.g. new session ID generation, new log/state file creation, or initial IPC handshake) rather than a general runtime incompatibility.

## stderr / crash log


============================================================
Bun v1.4.0 (f6d0fcd24) Windows x64 (baseline)
Windows v10.26200
CPU: sse42 avx avx2
Args: "<home>\AppData\Roaming\Claude\claude-code\2.1.219\claude.exe" "--output-format" "stream-json" "--verbose" "--input-format" "stream-json" "--effort" "high" "--model" "claude-sonnet-5" "--permission-prompt-tool" "stdio" "--all"...
Features: jsc standalone_executable claude_code
Elapsed: 15ms | User: 31ms | Sys: 0ms
RSS: 14.64 MB | Peak: 14.64 MB | Commit: 51.0 MB | Faults: 4211
panic(main thread): Segmentation fault at address 0x8
oh no: Bun has crashed. This indicates a bug in Bun, not your code.
To send a redacted crash report to Bun's team,
please file a GitHub issue using the link below:
 https://bun.report/1.4.0/<blob>.DLLurmLCSntdll.dll422qBA2AQ
============================================================

(Identical panic repeats twice in the log, both showing the same "Segmentation fault at address 0x8".)

## What I've tried

- Full uninstall and reinstall (same version reinstalled, v2.1.219) — did not fix the crash, since it's the same binary being restored, not a local corruption issue.
- Confirmed resuming/continuing existing conversations works reliably; only *new* conversations crash.

## Additional notes

- Windows build 26200 also appears in a similar report (#57053) involving Cowork's Hyper-V VM crashing on session start with a Bun segfault, which may be related.
- Possible relevant factor: antivirus/EDR software intercepting the new-file-creation step of session initialization (reported elsewhere as a contributing cause for similar Bun segfaults on Windows, e.g. Trend Micro hook DLLs). Have not yet confirmed whether an AV exclusion resolves this on my machine.

Steps to Reproduce

new conversation in claude cowork or claude code

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.24

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_