[BUG] Proxy CONNECT requests are missing the claude-cli User-Agent (inconsistent with tunneled requests)

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 identifies itself with User-Agent: claude-cli/<version> (external, cli) on its API requests — but when those requests go through an HTTP proxy, the CONNECT request that opens the tunnel carries no User-Agent at all. The unexpected behavior: a client that sets a UA everywhere else silently omits it on the one hop a non-intercepting proxy can actually read.

Example request as seen by proxy:

CONNECT api.anthropic.com:443 HTTP/1.1
Host: api.anthropic.com:443

The claude-cli UA is only sent on the real request inside the TLS tunnel, so a proxy that isn't doing full MITM interception cannot see it — and thus cannot attribute the connection to Claude Code at all.

Corporate/egress proxies that deliberately avoid TLS interception rely on the CONNECT preamble as the only visible layer. Because Claude Code is indistinguishable from a bare Node client there, allowlisting, auditing, and per-application routing of Claude Code traffic silently break.

What Should Happen?

The CONNECT request includes the same UA used for the API call, so the tunnel-establishment hop is attributable to Claude Code:

CONNECT api.anthropic.com:443 HTTP/1.1
Host: api.anthropic.com:443
User-Agent: claude-cli/2.1.197 (external, cli)

This is what other HTTP clients do — e.g. curl through the same proxy:

CONNECT api.anthropic.com:443 HTTP/1.1
Host: api.anthropic.com:443
User-Agent: curl/8.19.0
Proxy-Connection: Keep-Alive

Error Messages/Logs

Steps to Reproduce

1. Start a minimal logging proxy:

node -e 'require("net").createServer(c=>c.once("data",d=>console.log("\n--- CONNECT ---\n"+d.toString().trim()))).listen(8888,()=>console.log("listening 8888"))'

1. Point Claude Code at it (HTTPS_PROXY=http://127.0.0.1:8888) and make any request.
2. Observe the logged CONNECT preamble.

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.197 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Windows Terminal

Additional Information

_No response_