[BUG] Desktop app bundled claude-code 2.1.219 (Bun 1.4.0) deterministic startup segfault 0xFFFFFFFFFFFFFFFF on Windows 10 — Cowork "On your computer" unusable, no downgrade path

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?

Starting a Cowork task in "On your computer" mode spawns the bundled claude-code harness (claude.exe), which dies 68–112 ms after launch — before doing any work — with a Bun panic, exit code 3. The app retries and the second spawn crashes identically. 100% reproducible across multiple days.

Environment:

• Claude desktop app 1.24012.9 (Electron 42.7.0, Node 24.18.0)
• Bundled claude-code 2.1.219 at %APPDATA%\Claude\claude-code\2.1.219\claude.exe
• Bun v1.4.0 (f6d0fcd24) Windows x64 (baseline build)
• Windows 10 22H2 (build 19045), CPU: sse42/avx/avx2, 68 GB RAM

Full stderr:

Bun v1.4.0 (f6d0fcd24) Windows x64 (baseline)
Windows v10.19045
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" "--permission-prompt-tool" "stdio" ...
Features: jsc standalone_executable claude_code
Elapsed: 112ms | User: 31ms | Sys: 93ms
RSS: 0.14 GB | Peak: 0.14 GB | Commit: 0.17 GB | Faults: 34003
panic(main thread): Segmentation fault at address 0xFFFFFFFFFFFFFFFF

Ruled out:

• Corrupted download: deleted the entire %APPDATA%\Claude folder; the app recreated it and re-downloaded 2.1.219 fresh → identical crash on first use.
• User state/config: crash happens at startup on a clean, recreated data folder.
• Antivirus: no Defender detection/remediation events tied to the crash.
• App otherwise healthy: cloud Cowork sessions, chat and the Chrome native host all work normally on the same install.

Notes: signature matches the known 0xFFFFFFFFFFFFFFFF Bun startup-crash family on Windows (regression from the 2.1.110 → 2.1.114 switch to the Bun standalone). Related: #55219, #51477, #21469, #25630, oven-sh/bun#27003, oven-sh/bun#32586. This is the desktop-app-bundled variant: unlike the CLI (which can pin @anthropic-ai/claude-code@2.1.110 with DISABLE_AUTOUPDATER=1), the desktop app chooses the bundled version itself — no user-accessible downgrade, so local Cowork is fully unusable until a fixed build ships.

What Should Happen?

The bundled harness should start and run the local ("On your computer") Cowork session normally. Request: bundle a Bun build with the Windows startup-segfault fix (or a pure-Node fallback) for the desktop runner, or expose a version pin for the bundled component.

Error Messages/Logs

Claude Code process exited with code 3.
Bun v1.4.0 (f6d0fcd24) Windows x64 (baseline)
Windows v10.19045
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" "--permission-prompt-tool" "stdio" "--all"...
Features: jsc standalone_executable claude_code
Builtins: "bun:main"
Elapsed: 112ms | User: 31ms | Sys: 93ms
RSS: 0.14 GB | Peak: 0.14 GB | Commit: 0.17 GB | Faults: 34003 | Machine: 68.64 GB
panic(main thread): Segmentation fault at address 0xFFFFFFFFFFFFFFFF
(second consecutive spawn attempt crashes identically — Elapsed: 68ms, Faults: 33811)

Steps to Reproduce

1. Claude desktop app 1.24012.9 on Windows 10 22H2 (build 19045).
2. Start any Cowork task in "On your computer" mode (anything that spawns the bundled claude-code harness).
3. The harness (claude.exe 2.1.219, Bun v1.4.0) segfaults at 0xFFFFFFFFFFFFFFFF within 68–112 ms; the automatic retry crashes identically.
4. Reproduces 100% of the time — including after deleting %APPDATA%\Claude entirely and letting the app re-download the component fresh (rules out corrupted download).

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.110 (last pure-Node distribution; broken since the 2.1.114 switch to the Bun standalone)

Claude Code Version

2.1.219 (Claude Code) — desktop-app bundled component at %APPDATA%\Claude\claude-code\2.1.219\claude.exe. Version taken from the crash log/path; the binary itself segfaults on launch.

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

• The harness is spawned by the Claude desktop app (Cowork "On your computer" mode) over stdio — no terminal involved; Terminal/Shell field is N/A.
• Crash reproduces with a freshly re-downloaded component after deleting %APPDATA%\Claude entirely.
• Same-signature reports: #78436 (mid-session variant, Win11), #28789 (same address, auto-closed stale), #55219 (distinct 0x3C startup family; documents the 2.1.110→2.1.114 Bun regression), oven-sh/bun#27003, oven-sh/bun#32586.
• Cloud-mode Cowork on the same install works normally; only the local runner is affected.