GitHub write access fails with 403 despite connected GitHub integration (read access works)

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 GitHub integration is connected under Settings → Connectors → GitHub-Integration (shows "Disconnect" option). Read access to my own repository (SelRider/crumbcake) works fine — cloning, listing branches, reading files all succeed. However, write access consistently fails.

What Should Happen?

Push / branch creation should succeed since the GitHub integration is connected and shows as active.

Error Messages/Logs

git push fails: "fatal: unable to access '...': The requested URL returned error: 403"
GitHub API call fails: "403 Resource not accessible by integration"

This happens consistently across:
- Multiple Claude Code sessions
- A freshly created session
- A Cloud environment explicitly configured with "Trusted" network access

Tried disconnecting and reconnecting the GitHub integration in Settings → Connectors — no new GitHub authorization/permissions dialog appeared, and the issue persisted.

On the GitHub side, under github.com/settings/installations:
- "Installed GitHub Apps" shows no Claude/Anthropic app
- "Authorized OAuth Apps" shows no Claude/Anthropic app

Steps to Reproduce

1. Connect GitHub integration under claude.ai Settings → Connectors
2. Start a Claude Code session with a repository (SelRider/crumbcake) attached
3. Attempt to push a commit via git push origin <branch>
4. Attempt to create a branch/push via the GitHub MCP tools (create_branch, push_files)

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.220 (Claude Code)

Platform

Anthropic API

Operating System

Windows 10 10.0.19045 Build 19045

Terminal/Shell

Terminal.app (windows 10)

Additional Information

Claude Code on the web (Cloud Code), repository: SelRider/crumbcake (public repo, personal GitHub account)