/plugin install creates recursive nested cache on repeated installs

Steps to reproduce

1. /plugin marketplace add easyfan/skill-review
2. /plugin install skill-review@skill-review
3. Repeat step 2 (or reinstall)

Result

~/.claude/plugins/cache/<plugin-name>/ grows with recursive nesting:

cache/skill-review/
  skill-review/
    67bcbae6ee97/
      skill-review/
        67bcbae6ee97/
          skill-review/          ← repeats 30+ levels deep
            ...

Observed size: 11 MB for a plugin whose actual content is ~332 KB.

Expected behavior

Reinstall should overwrite the existing cache entry, not nest a new copy inside it.

Workaround

Manually delete the nested directories:

rm -rf ~/.claude/plugins/cache/skill-review/skill-review

Environment

• Claude Code: 2.1.88
• OS: macOS Darwin 25.3.0 (arm64)