[BUG] Claude Code inserts extra character into username when constructing ~/.claude/plans/ path

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 incorrectly constructs file paths by inserting an extra character into my macOS username, causing all plan file writes to fail with a permission error.

Correct username: user123udo (anonymized — ends in udo)
Claude Code constructs: user123undo with an extra n inserted before do

The cwd passed to each tool call is correct, but when Claude Code constructs the plans directory path independently — e.g. for the Write tool targeting ~/.claude/plans/ — it uses the wrong username.

Environment:

Claude Code version: 2.1.84–2.1.86 (reproducible across versions)
macOS
$HOME, $USER, whoami, and dscl RealName all return the correct username

Workaround:
None — plan files cannot be written, causing plan mode to silently fail every session.

What Should Happen?

Claude should be able to get and use the correct path when creating plan.md files

Error Messages/Logs

Error:
Write(/Users/<wrong-username>/.claude/plans/some-plan.md)
Error: EACCES: permission denied, mkdir '/Users/<wrong-username>'
Root cause hypothesis:
Claude Code derives the plans path from a source other than $HOME or cwd — possibly from the account display name, a cached value, or a separate username lookup that mangles the name. Environment variables $HOME, $USER, whoami, and dscl RealName all return the correct username.

Steps to Reproduce

Steps to reproduce:

macOS username containing a specific character sequence (details withheld for privacy)
Open Claude Code in any project
Trigger any task that causes plan file creation (plan mode)
Observe EACCES: permission denied, mkdir '/Users/<wrong-username>'

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.84–2.1.86 (reproducible across versions)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_