- Add GhTokenProvider to read GitHub tokens via `gh auth token` - Extend TokenResolver policy: ENV → gh → keyring (validate) → prompt (overwrite) - Introduce provider-specific token validation for GitHub - Ensure invalid keyring tokens trigger interactive re-prompt and overwrite - Add end-to-end integration test covering gh → keyring → prompt flow - Clean up credentials package exports and documentation https://chatgpt.com/share/69418c81-6748-800f-8fec-616684746e3c