Cowork: artifact deletion from UI leaves orphaned folder on disk

Summary

When deleting an artifact from the Cowork UI, the entry is removed from artifacts.json but the corresponding folder in ~/Documents/Claude/Artifacts/ is not cleaned up. This causes create_artifact to fail with:

A folder for "lp-dashboard" already exists in Documents/Claude/Artifacts. It may be from a previous deletion or another account. Choose a different id.

Steps to reproduce

1. Create an artifact in Cowork (e.g., id lp-dashboard)
2. Delete it from the Cowork UI
3. Verify the entry is gone from artifacts.json
4. Verify ~/Documents/Claude/Artifacts/lp-dashboard/ still exists on disk
5. Try to create a new artifact with the same id → error

Expected behavior

Deleting an artifact from the UI should also remove the folder from ~/Documents/Claude/Artifacts/.

Actual behavior

• artifacts.json entry is removed ✅
• ~/Documents/Claude/Artifacts/<id>/ folder persists ❌
• Re-creating an artifact with the same id fails ❌

Environment

• macOS (Darwin 24.6.0)
• Claude Desktop with Cowork mode
• Session storage: ~/Library/Application Support/Claude/local-agent-mode-sessions/
• Artifact storage: ~/Documents/Claude/Artifacts/

Additional context

In one session, 11 artifacts were tracked in artifacts.json while 14 folders existed on disk — the 3 extra were orphans from prior UI deletions.