The correct options are The same repository that contains the calling workflow, A public repository when organizational policy permits use of public reusable workflows, and A private repository that has been configured to allow access for reuse.

Calling from the same repository that contains the calling workflow is straightforward because the reusable workflow file lives in the same codebase and is enabled with the workflow_call trigger. You reference it by path and ref and GitHub enforces access within the repository boundary.

You can also call from a public repository when organizational policy permits use of public reusable workflows. This requires the organization or enterprise settings to allow actions and reusable workflows from public repositories. When permitted, you reference the workflow by owner and repository and ref and GitHub enforces the policy and permission checks.

It is additionally possible to call from a private repository that has been configured to allow access for reuse. The called private repository must explicitly grant access for reuse to the requesting repositories or to the organization scope. With that configuration in place, the caller can reference the reusable workflow and GitHub honors the access controls and token permissions.

A Docker container image hosted on Docker Hub is not a valid source for a reusable workflow because workflows must reside in GitHub repositories under the .github/workflows directory and be invoked with workflow_call. A container image can host an action implementation but it does not host a reusable workflow.

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