claude-code - 💡(How to fix) Fix Native update/install fails with 'socket connection was closed unexpectedly' behind proxy — undici TLS incompatibility

Description

claude update and claude install consistently fail with:

Error: The socket connection was closed unexpectedly. For more information, pass `verbose: true` in the second argument to fetch()

This occurs when running behind a proxy (system proxy enabled). The issue is specific to the bundled undici fetch() inside claude.exe — all other methods of accessing the same URL work fine.

Environment

• OS: Windows 11
• Claude Code version: 2.1.153 (native install)
• System Node.js: v24.15.0
• Proxy: HTTP/HTTPS proxy on localhost

Reproduction

1. Run behind a proxy
2. Execute claude update or claude install
3. Fails immediately with the socket error

What works vs. what doesn't

Root cause analysis

The TLS handshake fails specifically inside the bundled undici in claude.exe. This was confirmed by:

# System Node.js fetch works fine
node -e "fetch('https://downloads.claude.ai/claude-code-releases/latest').then(r => r.text()).then(console.log)"
# Output: 2.1.153 ✅

# But claude.exe fails on the same URL
claude update
# Error: socket connection was closed unexpectedly ❌

Setting NODE_TLS_REJECT_UNAUTHORIZED=0 does not resolve the issue for claude.exe, suggesting the problem is deeper than certificate validation — likely an incompatibility between the bundled undici version's TLS implementation and certain proxy configurations.

Additional context

• The same claude.exe version (2.1.153) works on one machine but fails on another with the same system Node.js version (v24.15.0), suggesting the bundled Node.js/undici version may differ or there's a subtle environmental difference in how the binary interacts with the proxy.
• Related issues: #60133 (SO_KEEPALIVE analysis), #37801 (update fails but curl works), #13498 (GCS timeout)

Suggestion

Consider adding proxy support to the native updater (respecting HTTP_PROXY/HTTPS_PROXY environment variables) or falling back to https.get when fetch() fails.