OAuth login fails with "Invalid code. Please make sure the full code was copied" despite entering the correct code

Environment:

• OS: Windows 11 Pro (10.0.26200)
• Shell: PowerShell / Git Bash (MSYS2)
• Claude Code invoked via: /login

Steps to reproduce:

1. Run /login in Claude Code
2. Complete the browser-based auth flow and receive a verification code via email
3. Copy the code from the email and paste it into the terminal prompt
4. Submit the code

Expected behavior:
Login completes successfully.

Actual behavior:
Login fails with:

OAuth error: Invalid code. Please make sure the full code was copied

This happens even when the code is copied correctly and entered promptly. I've retried multiple times (/login interrupted and restarted each time) with the same result, including careful re-copying of the code to rule out stray whitespace/formatting issues.

Additional notes:

• Tried both retyping manually and pasting via plain text to rule out smart-quote/whitespace corruption.
• Multiple /login attempts in the same session were interrupted before this — unclear if a stale/previous auth session could be interfering.