[BUG] Claude Code Web: Proxy blocks CONNECT tunnel to npm.pkg.github.com (403), preventing yarn install of private packages

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?

yarn install fails on Claude Code Web when the project depends on private packages from npm.pkg.github.com. The proxy blocks the HTTPS CONNECT tunnel with statusCode=403, preventing yarn from reaching the registry at all.

This is related to #11078, which was marked as resolved on 2026-01-22. However, the issue persists with a different error pattern — instead of 401/403 from the registry, the proxy itself rejects the tunnel before the request reaches the registry.

Error

➤ YN0001: │ RequestError: tunneling socket could not be established, statusCode=403
    at ClientRequest.<anonymous> (/home/user/web-app/.yarn/releases/yarn-4.0.2.cjs:147:14258)

Root Cause

The Claude Code Web container forces all HTTP(S) traffic through a JWT-authenticated proxy via environment variables:

GLOBAL_AGENT_HTTP_PROXY=http://container_container_<id>--claude_code_remote--<hash>:jwt_<token>@...

When yarn attempts to create a CONNECT tunnel through this proxy to npm.pkg.github.com, the proxy returns 403 Forbidden — indicating these domains are not in the proxy's allowlist.

What Should Happen?

yarn install should be able to fetch packages from npm.pkg.github.com when proper authentication is configured in .yarnrc.yml, just as it works on a local machine.

Steps to Reproduce

1. Open a Claude Code Web session for a repository with private @org/* packages on GitHub Packages
2. The .yarnrc.yml should have:

``yaml
npmScopes:
org-name:
npmAlwaysAuth: true
npmAuthToken: '${NODE_AUTH_TOKEN}'
npmRegistryServer: 'https://npm.pkg.github.com'
``

1. Run yarn install
2. Observe tunneling socket could not be established, statusCode=403

Attempted Workarounds (All Failed)

| Attempt | Result |
|---------|--------|
| yarn install | tunneling socket could not be established, statusCode=403 |
| yarn install --mode skip-build | Same 403 tunneling error |
| yarn install --immutable | Same 403 tunneling error |
| unset HTTP_PROXY HTTPS_PROXY && yarn install | Same error — GLOBAL_AGENT_HTTP_PROXY is set at container level and cannot be unset |
| HTTPS_PROXY= HTTP_PROXY= yarn install | Same error — proxy is enforced via global agent |
| yarn config unset httpProxy/httpsProxy | "Configuration doesn't contain setting" — proxy is injected via env vars, not yarn config |
| yarn config set enableNetwork false && yarn install | YN0080 — private packages not in local .yarn/cache |

Key Observation

The proxy cannot be bypassed from within the container. The GLOBAL_AGENT_HTTP_PROXY environment variable intercepts all outbound HTTPS connections at the Node.js level, and the proxy returns 403 for any CONNECT tunnel to npm.pkg.github.com.

Claude Model

Other

Is this a regression?

Related to #11078 which was closed as resolved on 2026-01-22, but the underlying issue persists with a different symptom (proxy tunnel rejection instead of auth header stripping).

Claude Code Version

Claude Code Web (latest)

Platform

Web

Operating System

N/A (Claude Code Web)

Terminal/Shell

N/A (Claude Code Web)

Additional Information

• Yarn version: 4.0.2 (Berry, with Plug'n'Play)
• Node linker: node-modules
• Cached packages: 2,747 packages exist in .yarn/cache, but private packages from npm.pkg.github.com are not among them
• The proxy successfully handles git operations (push/pull to GitHub) but does not allow tunneling to npm.pkg.github.com