Plugin from personal marketplace disappears after every app restart (Cowork desktop)

Bug description

Plugins installed from a personal GitHub marketplace disappear after every Claude desktop app restart. The plugin installs fine and works during the session, but on quit + reopen it's gone. The toggle in the top-right also becomes non-functional. Multiple users on the same marketplace experience this.

Steps to reproduce

1. Add a personal marketplace via Customize → Plugins → Add marketplace → cruciate-hub/marketing-team
2. Install the product-marketing-team plugin
3. Use it — works fine
4. Quit Claude (Cmd+Q) and reopen
5. Plugin is gone, marketplace tab shows it as uninstalled

What I've tried

• Reinstalling 3+ times via the UI — same result every time
• Manually adding enabledPlugins and extraKnownMarketplaces to ~/.claude/settings.json:

{
  "extraKnownMarketplaces": {
    "cruciate-hub": {
      "source": {
        "source": "github",
        "repo": "cruciate-hub/marketing-team"
      }
    }
  },
  "enabledPlugins": {
    "product-marketing-team@cruciate-hub": true
  }
}

• Verified ~/.claude/plugins/known_marketplaces.json has the marketplace registered with correct installLocation
• Verified ~/.claude/plugins/marketplaces/cruciate-hub/ is fully cloned with correct marketplace.json and plugin.json
• Plugin is not in blocklist.json
• Repo is public, GitHub Pages works, all file paths resolve

Despite all config files being correct on disk, the app does not load the plugin on startup.

Environment

• Claude desktop app (Cowork), macOS
• Marketplace: public GitHub repo with .claude-plugin/marketplace.json at root
• Plugin: 9 skills, plugin.json in skills/.claude-plugin/
• Two users affected (different machines, same marketplace)

Possibly related

• #10565 (closed but same symptom)
• #20661 (duplicate of #17832 — enabledPlugins not synced)
• #17089 (local plugins don't persist after 2.1.x)