Plugin installed with project scope becomes invisible in /plugin UI for all other projects

Bug Description

When a plugin is installed with scope: "project" from one project, it becomes completely invisible in the /plugin UI for all other projects. There is no way to install or enable the same plugin in a different project without manually editing installed_plugins.json.

Steps to Reproduce

1. Open Claude Code in Project A
2. Run /plugin and install a plugin (e.g., slack@claude-plugins-official)
3. The plugin gets installed with scope: "project" and projectPath pointing to Project A
4. Open Claude Code in Project B
5. Run /plugin — the slack plugin does not appear in the list at all

Expected Behavior

• The plugin should appear in the /plugin list for other projects, allowing the user to install/enable it there as well
• Or, there should be an option to install a plugin as scope: "user" (available globally) vs scope: "project"

Actual Behavior

• The plugin is completely absent from the /plugin UI in other projects
• The only workaround is to manually delete the plugin entry from ~/.claude/plugins/installed_plugins.json and reinstall it

Relevant Entry in installed_plugins.json

"slack@claude-plugins-official": [
  {
    "scope": "project",
    "installPath": "...",
    "version": "...",
    "projectPath": "/path/to/project-a"
  }
]

Once this entry exists, no other project can see or install this plugin via /plugin.

Environment

• Claude Code v2.1.45
• macOS (Darwin 24.6.0)