[BUG] False positive: macOS username ending in . triggers "suspicious Windows path pattern" on every write

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?

Environment

• OS: macOS (Darwin 24.3.0)
• Claude Code: <run claude --version and paste>
• macOS short username: blairco. (legitimately ends in a dot)
• Home directory: /Users/blairco.

Bug
Every Write/Edit tool call in any worktree under my home directory is blocked with:
"Claude requested permissions to write to /Users/blairco./Downloads/... which contains a
suspicious Windows path pattern that requires manual approval."

The heuristic appears to flag any path component ending in . as a Windows reserved-name
pattern. On macOS, a trailing dot in a username is legal and my real home is /Users/blairco.,
so every single path I touch trips the check.

Impact

• Cannot use Claude Code without manually approving every write.
• Adding the path to permissions.allow in ~/.claude/settings.json does NOT suppress it,

which suggests the heuristic runs before the allow-list is consulted.

• Affects every worktree, every project, every session.

Repro

1. macOS user with short name ending in . (e.g. blairco.)
2. cd ~/anything && claude
3. Ask Claude to edit any file → prompt fires.

Expected
The Windows-reserved-name check should only apply on Windows, or should validate the final
path component rather than any component containing a . followed by /.

Workaround
sudo ln -s /Users/blairco. /Users/blairco and launching from the dotless path silences it,
but that's a per-machine band-aid.

What Should Happen?

Environment

• OS: macOS (Darwin 24.3.0)
• Claude Code: <run claude --version and paste>
• macOS short username: blairco. (legitimately ends in a dot)
• Home directory: /Users/blairco.

Bug
Every Write/Edit tool call in any worktree under my home directory is blocked with:
"Claude requested permissions to write to /Users/blairco./Downloads/... which contains a
suspicious Windows path pattern that requires manual approval."

The heuristic appears to flag any path component ending in . as a Windows reserved-name
pattern. On macOS, a trailing dot in a username is legal and my real home is /Users/blairco.,
so every single path I touch trips the check.

Impact

• Cannot use Claude Code without manually approving every write.
• Adding the path to permissions.allow in ~/.claude/settings.json does NOT suppress it,

which suggests the heuristic runs before the allow-list is consulted.

• Affects every worktree, every project, every session.

Repro

1. macOS user with short name ending in . (e.g. blairco.)
2. cd ~/anything && claude
3. Ask Claude to edit any file → prompt fires.

Expected
The Windows-reserved-name check should only apply on Windows, or should validate the final
path component rather than any component containing a . followed by /.

Workaround
sudo ln -s /Users/blairco. /Users/blairco and launching from the dotless path silences it,
but that's a per-machine band-aid.

Error Messages/Logs

Steps to Reproduce

Open any new chat

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.128 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_