[gabisonia]

Description

A root-owned Erlang cookie in the native-delay image prevents RabbitMQ from starting as rabbitmq, leaving the native-delay tests without a broker.

Remove any cookie after offline plugin setup so RabbitMQ creates its own at startup. Run the Compose fixture as rabbitmq and check the runtime user and broker health in CI. Document the separate Docker Hub credentials error reported in the issue.

Related Issues

Fixes #4566

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the Contributing Guide
• I have checked the relevant fixture documentation in docker/RabbitMQ/README.md
• I have added/updated XML documentation for any public API changes — no public API changes
• I have added/updated tests as appropriate
• My changes follow the existing code style and conventions

Validation

• Docker and Podman 5.8.2 with applehv on macOS: nonroot startup, cookie ownership, plugin availability, and restart passed.
• Native-delay suites on each engine: 54 sync tests and 103 async tests passed on each of .NET 9 and .NET 10. Total: 628 executions, no failures or skips.
• A temporary build with a root-owned cookie reproduced the exact eacces error on both engines; the same build with this fix started successfully.
• The CI startup commands passed locally. The startup check rejected the image containing the unreadable cookie.
• git diff --check passed. Workflow lint has no new findings compared with master.

Additional Notes

Clean builds of the unchanged image also started successfully here. The controlled reproduction verifies the reported cookie-permission condition, but the original trigger for cookie creation remains unconfirmed. This change does not repair cookies in existing volumes.

Please merge with a merge commit, as requested by the contributing guide.

[iancooper]

Thanks @gabisonia