Unresolvable TypeError: fetch failed on Clean WSL Installation

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Environment

• Platform (select one):
• [x] Anthropic API
• Claude CLI version: 1.0.30 (Claude Code)
• Operating System: Windows 11 with WSL 2 (Ubuntu)
• Terminal: Windows Terminal (Ubuntu Profile)

Bug Description

The claude CLI tool consistently fails with API Error (Connection error.) which traces to a TypeError: fetch failed on any command that requires a network connection (e.g., /init). This occurs on a completely clean, fresh WSL (Ubuntu) installation with a correct Node.js environment, and persists after all known WSL networking workarounds have been applied.

Steps to Reproduce

1. On a Windows 11 machine, install a fresh instance of WSL (Ubuntu).
2. Install Node.js v20.x via the official NodeSource repository (curl -fsSL https://deb.nodesource.com/setup_20.x | sudo -E bash - && sudo apt-get install -y nodejs).
3. Configure npm to use a local directory: npm config set prefix '~/.npm-global' and add ~/.npm-global/bin to the PATH.
4. Install the CLI: npm install -g @anthropic-ai/claude-code.
5. Navigate to any project directory.
6. Run claude.
7. At the > prompt, run /init.

Expected Behavior

The /init command should successfully connect to the Anthropic API, analyze the codebase, and generate a CLAUDE.md file.

Actual Behavior

The command fails with repeated API Error (Connection error.) messages. The underlying error is a TypeError: fetch failed.

Additional Context

This appears to be a critical application-level issue specific to the WSL environment, as all underlying system and Node.js network diagnostics succeed.

Key Diagnostic Information:

• curl -v https://api.anthropic.com/v1/health succeeds.
• node -e "fetch('https://api.anthropic.com/v1/health')" succeeds.

Failed Mitigation Attempts:
We have exhaustively tried every common solution, none of which resolved the application's specific error:

• Forcing Node.js DNS to ipv4first via NODE_OPTIONS.
• A full WSL network reconfiguration (wsl --shutdown, .wslconfig set to networkingMode=mirrored).
• System-wide disabling of IPv6 in WSL via sysctl.
• Running on a fresh WSL instance with a correct Node.js installation (no nvm).

This indicates a probable application-level issue (e.g., a bundled undici version, a custom network agent, or a certificate problem) that is incompatible with the WSL environment.