Plugin cache: old versions never garbage collected on autoUpdate

Summary

When a plugin has autoUpdate: true in known_marketplaces.json, Claude Code downloads each new version into a fresh hash-named directory under ~/.claude/plugins/cache/<marketplace>/<plugin>/<hash>/, and updates installed_plugins.json to point to the new directory. However, the old version directories are never deleted, causing unbounded cache growth over time.

Reproduction

1. Install a plugin from a marketplace with autoUpdate: true
2. Let the plugin receive several updates over days/weeks
3. Check the cache directory:

``
ls ~/.claude/plugins/cache/<marketplace>/<plugin>/
``

1. Observe multiple hash directories, each a full copy of the repo

Impact observed

On a real user setup with the agent-deck plugin (~135 MB per version):

• 9 cached versions accumulated over ~3 months
• 1.2 GB of dead cache (only the latest version is referenced by installed_plugins.json)
• 301 stale temp_git_* directories (~420 MB) also accumulated in the plugin cache root, which are temporary git clones from the download step that are never cleaned up

Total wasted disk: ~1.5 GB

This likely contributes to slower session startup as Claude Code scans the plugin cache directory to discover skills, hooks, and agents.

Expected behavior

After a successful plugin update:

1. The old version directory should be removed from the cache once the new version is confirmed working
2. temp_git_* temporary directories should be cleaned up after successful installation

Additional context

• Affects all plugins with autoUpdate: true, but most visible with larger repos
• Manually deleting old cache directories during a live session causes breakage (Claude Code appears to hold in-memory references). Cleanup is only safe between sessions.
• A claude plugins gc command or automatic post-update cleanup would solve this

Environment

• Claude Code CLI (latest as of 2026-03-19)
• macOS (Apple Silicon)