Fixing GitHub Actions 'reusable workflow was not found' errors

This error means a uses: reference was correctly formatted but could not be resolved to a workflow file. GitHub checks the file path, the ref on the target repository, read access for the caller, and whether the file declares workflow_call, stopping at the first failure. Runs with this error end instantly with no jobs or logs, and the annotation shows a chain of references where the last entry is the one that failed. That failing reference is often inside a nested workflow the user did not write. Developers are advised to read the chain bottom-up and verify the path, ref, and access against the owning repository.