[BUG] User skill not appearing in Claude Desktop UI despite correct file placement (Windows, post-April 23 regression)

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)
• [ ] I am using the latest version of Claude Code

What's Wrong?

Environment
Platform: Windows
Claude Desktop version: Latest (updated May 13, 2026)
Date: May 13, 2026
Affected skill: uat-test-design
Issue
User skill correctly placed in /mnt/skills/user/uat-test-design/SKILL.md does not appear in Claude Desktop's Settings → Skills → Personal skills list, despite: - Correct file location - Correct permissions (600, identical to working skills) - Valid YAML frontmatter - Proper directory structure - Multiple restarts and updates

Working skills (for comparison)
These skills DO appear in the UI and were created on April 23, 2026:

-rw------- 1 root root 9911 Apr 23 10:10 functional-test-design/SKILL.md
-rw------- 1 root root 7433 Apr 23 10:04 release-notes/SKILL.md
Non-working skill
This skill does NOT appear in UI, created May 11, 2026:

-rw------- 1 root root 13326 May 11 15:33 uat-test-design/SKILL.md
Verification performed

1. File location verified

$ ls -la /mnt/skills/user/uat-test-design/
total 24
drwxr-xr-x 2 root root 4096 May 11 15:33 .
drwxr-xr-x 5 root root 4096 May 11 15:33 ..
-rw------- 1 root root 13326 May 11 15:33 SKILL.md

1. Permissions corrected to match working skills

Changed from 644 to 600 to match functional-test-design and release-notes

1. YAML frontmatter validated

✅ YAML is valid!
Name: uat-test-design
Description length: 693

1. File encoding verified

$ file /mnt/skills/user/*/SKILL.md
functional-test-design/SKILL.md: Unicode text, UTF-8 text
release-notes/SKILL.md: Unicode text, UTF-8 text
uat-test-design/SKILL.md: Unicode text, UTF-8 text

1. Multiple restarts performed

Closed and reopened Claude Desktop (3 times)
Updated Claude Desktop to latest version and restarted
No change in behavior
Related existing issues
This appears related to ongoing skill mounting/registration bugs: - #26254 - User skills metadata registered but files not mounted - #26998 - Skills not saving/loading on Windows, /mnt/skills/user/ empty - #31597 - Skills from ~/.claude/skills/ not shown in Customize panel

Timeline context
April 23, 2026: User successfully created functional-test-design and release-notes skills (both working)
May 11, 2026: User created uat-test-design skill (not working)
April 23 was the day Anthropic published the post-mortem about March-April regressions
Suggests NEW regression introduced after April 23 fix
Expected behavior
Skill should appear in Settings → Skills → Personal skills list alongside functional-test-design and release-notes.

Actual behavior
Skill file exists in correct location with correct permissions, but does not appear in UI.

Workaround
Manual upload via UI "+" button works, but defeats the purpose of programmatic skill creation during chat sessions.

Request
Please investigate why skills created after April 23, 2026 are not being registered in Claude Desktop's UI, while skills created on April 23 still work correctly.

What Should Happen?

The skills should be saved as expected

Error Messages/Logs

Steps to Reproduce

Everything is explained in the description

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.7196.0

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_