[BUG] MacOS: Failed to start OAuth callback server: Failed to start server. Is port 0 in use?

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?

Issue Summary:
Persistent "OAuth error: Failed to start OAuth callback server: Failed to start server. Is port 0 in use?" preventing authentication with Claude subscription account.

Environment:
macOS (Macbook Pro M2)
iTerm terminal
Claude Code version 2.0.37
Fresh installation completed
No VPN, firewall disabled, no proxy restrictions

Steps Taken:
Multiple fresh installations and reinstalls
Removed duplicate installations
Ran claude install --force and claude migrate-installer
Cleared authentication: rm -rf ~/.config/claude-code/auth.json
Complete terminal restarts
Complete computer restarts
Verified network connectivity to required endpoints

What Should Happen?

Expected Behavior:
Should successfully authenticate with Claude subscription account (option 1).

Actual Behavior:
OAuth callback server fails to start, preventing any authentication.
OAuth error: Failed to start OAuth callback server: Failed to start server. Is port 0 in use?

<img width="571" height="291" alt="Image" src="https://github.com/user-attachments/assets/ff95f0ac-9e51-4083-b28a-9941994861a1" />
<img width="571" height="254" alt="Image" src="https://github.com/user-attachments/assets/7891f70a-f7c5-4402-8b04-4dd1f4cda15f" />

Error Messages/Logs

OAuth error: Failed to start OAuth callback server: Failed to start server. Is port 0 in use?

When selecting option: 1. Claude account with subscription · Pro, Max, Team, or Enterprise

Steps to Reproduce

1. $ claude

1. Let's get started.

Choose the text style that looks best with your terminal
To change this later, run /theme

❯ 1. Dark mode ✔ <- select

1. Claude Code can be used with your Claude subscription or billed based on API usage through your

Console account.

Select login method:

❯ 1. Claude account with subscription · Pro, Max, Team, or Enterprise <- select

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.37

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_