[BUG] Plugin marketplace sync error "Claude GitHub App is not installed on this repository" despite app being correctly installed

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The Cowork plugin marketplace at duet-labs/aix started failing to sync on 2026-05-06 with the
error:

▎ Authentication with GitHub failed. Check that the Claude GitHub App is installed on this
▎ repository.
▎ GitHub authentication failed. The Claude GitHub App is not installed on this repository.
▎ Install it to grant access.

The Claude GitHub App is installed on the repository with appropriate read access. The repo is
private, owned by the duet-labs GitHub org, hosted on github.com (not Enterprise Server).

Environment:

• Platform: Cowork plugin marketplace (claude.ai)
• GitHub repo: duet-labs/aix (private, org-owned)
• App installed: Claude / Anthropic GitHub App
• Repository access: granted to duet-labs/aix

What I've already tried:

• Uninstalled and reinstalled the GitHub App on the repo
• Confirmed duet-labs/aix appears in the app's allowed repository list
• Validated marketplace.json and plugin.json against the official schemas at

https://code.claude.com/docs/en/plugin-marketplaces — both conform

What Should Happen?

Cowork should sync the marketplace and recognize the three plugins (aix, people, finance).

Error Messages/Logs

Persistent "Claude GitHub App is not installed" sync error, even though the app is correctly     
  installed and configured.

Steps to Reproduce

Steps to Reproduce:

1. Open Cowork on claude.ai
2. Navigate to plugin marketplaces
3. Locate duet-labs/aix
4. Sync banner shows "1 sync error" with the message above
5. All three plugins show "Not available" in the access column

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.132 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

This appears to be the same backend indexing issue described in #21377, #30872, #12839, #16256,
#18467. Other users in those threads report the symptom resolved after Anthropic engineers
manually reset the affected repo's index server-side.
Request: could you reset the plugin-marketplace backend index for duet-labs/aix?