Custom skills deleted server-side — 404 on sync, UI delete button non-functional

Bug Description

Two custom user-created skills are returning 404 from Anthropic's servers during skills sync, but cannot be deleted from the Capabilities UI. The delete button appears to fire but does not remove the skills. This forced a multi-hour diagnostic and workaround session consuming significant Pro/pay-as-you-go context.

Environment

• Claude Desktop v1.1.4010 (Windows 11 Pro, 10.0.26200)
• Skills plugin with 13 active skills (mix of user-created and Anthropic-provided)

Steps to Reproduce

1. Create custom skills via skill-creator (these were created 2026-02-17)
2. Skills work normally for ~6 days
3. On 2026-02-23, skills sync fails with 404 for both skill IDs:

• skill_01WsLgRrYSShb9Jfuw3S4Kbm ("windows-mcp-protocols")
• skill_017QsUd6QVWeoT5Vg13YaUm9 ("amerix-tandem-operations")

1. Attempt to delete via Capabilities tab three-dot menu → "Delete" → skill remains in list
2. Toggle skills off → skills show as disabled but persist
3. Manually edit local manifest.json to remove entries → cloud sync re-adds them on next Desktop launch

Error Logs (from %APPDATA%\Claude\logs\main.log)

[error] [SkillsPlugin] Failed to download windows-mcp-protocols: 
  404 Not Found: skill_01WsLgRrYSShb9Jfuw3S4Kbm
[error] [SkillsPlugin] Failed to download amerix-tandem-operations: 
  404 Not Found: skill_017QsUd6QVWeoT5Vg13YaUm9

What Happened

• Skills content was deleted server-side without user action
• Skills were never cached locally (no folder in skills-plugin cache)
• UI delete button fails silently — no error, no removal
• Cloud sync overwrites local manifest edits, re-adding dead skill entries
• "Replace" via skill-creator with same name prompts for overwrite but does not update the dead skill IDs with new content

Impact

• ~2 hours of diagnostic time across two agents (Claude Code + Claude Desktop)
• Significant Pro subscription context consumed troubleshooting
• Pay-as-you-go API tokens used on failed skill-creator replace attempts
• Had to rebuild both skills from scratch with new names as workaround
• Dead skills permanently visible in Capabilities UI (toggled off, cannot be removed)

Workaround

Created replacement skills with "-v2" suffix names to bypass the dead skill IDs. Original dead entries remain as cosmetic ghosts in the Capabilities tab — disabled but undeletable.

Expected Behavior

1. User-created skills should not be deleted server-side without user action
2. The delete button in Capabilities should actually delete skills
3. If a skill 404s, the sync should offer to remove the dead reference rather than silently failing and re-adding it
4. Local manifest edits should not be overwritten by cloud sync for skills that no longer exist server-side

Request

Please remove the two dead skill IDs from my account registry so they stop appearing in the Capabilities UI. And please investigate why user-created skill content was deleted server-side.