[BUG]: Claude Code VSCodium extension: login fails despite API key present in config.json

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?

The Claude Code extension in VSCodium shows "Not logged in - Please run /login" and will not proceed, despite the API key being correctly stored in ~/.claude/config.json. The OAuth login flow appears to complete successfully in the browser but does not signal back to VSCodium. Additionally, each failed login attempt silently generates a new API key in the Anthropic Console.

What Should Happen?

Either the OAuth callback should successfully signal VSCodium after browser login completes, or the API key already present in ~/.claude/config.json should be sufficient to authenticate without requiring the OAuth flow again.

Error Messages/Logs

None displayed. The extension silently returns to the three login options after the browser OAuth flow completes.

Steps to Reproduce

1. Install Claude Code extension in VSCodium on Windows
2. Open the Claude Code panel
3. Run /login and select "Anthropic Console"
4. Approve the browser link when prompted
5. Browser opens and displays "Build something great. You can now close this window."
6. Return to VSCodium — extension still shows "Not logged in - Please run /login"
7. Check ~/.claude/config.json — API key is present under primaryApiKey
8. Check Anthropic Console API Keys — a new key was generated by each login attempt
9. Repeat /login attempts produce the same result regardless

Claude Model

Other

Is this a regression?

I don't know

Last Working Version

N/A

Claude Code Version

Unknown — claude is not on PATH in VSCodium's integrated terminal

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

• The extension is partially functional — it displays the user's question in the panel title, suggesting it is reading input, but then returns to the login screen
• The Claude Code CLI (claude) is not accessible via PATH, so CLI-based workarounds are unavailable

Setting ANTHROPIC_API_KEY as a Windows User environment variable did not resolve the issue

• Issue #1253 touches on VSCodium support but describes a different problem (/ide detection rather than login)
• The root cause appears to be that VSCodium handles the vscode:// URI callback scheme differently than Microsoft VS Code, preventing the OAuth completion signal from reaching the extension

NOTE: This issue was mostly generated by Claude after a long session which it eventually described as "going in circles". It also recommended I generate a new API key and add that key to this issue, which is a bad idea.
:-)