[BUG]

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 crashes immediately on startup across all Windows entry points (VS Code extension, Claude Desktop app, CLI) with a Bun runtime panic: integer does not fit in destination type. The crash occurs within 1-2 seconds of launch, before any user interaction.

The bundled Bun v1.3.14 triggers this known bug on Windows 11 x64 machines with 16 GB RAM. Fresh reinstalls (npm and extension) do not resolve the issue since they all ship the same affected Bun version.

Crash log (CLI):
Bun v1.3.14 (2a41ca97) Windows x64 (baseline)
Windows v.win11_dt
CPU: sse42 avx avx2
RSS: 0.31GB | Peak: 0.31GB | Commit: 0.48GB | Machine: 16.86GB
panic(main thread): integer does not fit in destination type
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

Affected entry points:

• CLI (claude via npm @anthropic-ai/claude-code@latest, v2.1.172)
• VS Code extension (exit code 3)
• Claude Desktop app (claude.exe v2.1.170)

Root cause: Bun PR [oven-sh/bun#29327](https://github.com/oven-sh/bun/pull/29327) (merged April 15, 2026) fixes the uv_fs_read ssize_t-to-int truncation, but Claude Code has not yet shipped a build with this fix.

What Should Happen?

Voici un texte prêt à coller :

Claude Code should start normally without crashing. The bundled Bun runtime (currently v1.3.14) should include the fix from Bun PR #29327 (merged April 15, 2026), which resolves the uv_fs_read ssize_t-to-int truncation causing the "integer does not fit in destination type" panic on Windows x64 machines with 16 GB RAM. This affects both the VS Code extension, the Claude Desktop app, and the standalone CLI — all three bundle the same unfixed Bun binary.

Error Messages/Logs

CLI (PowerShell):
Bun v1.3.14 (2a41ca97) Windows x64 (baseline)
Windows v.win11_dt
CPU: sse42 avx avx2
Args: "C:\Users\max_c\AppData\Roaming\npm\node_modules\@anthropic-ai\claude-code\bin\claude.exe"
Features: Bun.stderr(2) Bun.stdin(2) Bun.stdout(2) fetch(3) jsc spawn(8) standalone_executable yaml_parse(26) claude_code
Elapsed: 1779ms | User: 1187ms | Sys: 750ms
RSS: 0.31GB | Peak: 0.32GB | Commit: 0.47GB | Faults: 82465 | Machine: 16.86GB
panic(main thread): integer does not fit in destination type
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

Claude Desktop app:
Claude Code process exited with code 3
Bun v1.3.14 (521eedd6) Windows x64 (baseline)
Windows v.win11_dt
CPU: sse42 avx avx2
Args: "<home>\AppData\Roaming\Claude\claude-code\2.1.170\claude.exe" "--output-format" "stream-json" "--verbose" "--input-format" "stream-json" "--effort" "high" "--model" "claude-opus-4-8" "--permission-prompt-tool" "stdio" "--all"
Elapsed: 1284ms | User: 843ms | Sys: 562ms
RSS: 0.34GB | Peak: 0.34GB | Commit: 0.56GB | Faults: 86970 | Machine: 16.86GB
panic(main thread): integer does not fit in destination type
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

VS Code extension:
Error: Claude Code process exited with code 3
View output logs · Troubleshooting resources

Steps to Reproduce

1. Use a Windows 11 x64 machine with ~16 GB RAM
2. Install Claude Code via npm: npm install -g @anthropic-ai/claude-code@latest
3. Run claude in PowerShell
4. Bun crashes instantly with panic(main thread): integer does not fit in destination type

Alternative reproduction paths (same crash):

• Open VS Code → Claude Code extension panel → "Error: Claude Code process exited with code 3"
• Open Claude Desktop app → Claude Code feature → same Bun panic

No user interaction required — the crash occurs during Bun runtime initialization, before any prompt or API call.

Environment:

• Windows 11 x64 (native, build win11_dt)
• CPU: sse42 avx avx2
• RAM: 16.86 GB
• Bun: v1.3.14 (bundled in Claude Code)
• Node.js/npm: used only for installation

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

CLI: 2.1.172 Desktop app: 2.1.170 VS Code extension: latest (same Bun v1.3.14 bundled)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_