Problem: Registry login fails silently if secrets aren't configured - Empty FORGEJO_REGISTRY_USER/TOKEN → docker login hangs/fails - No clear error message about missing credentials Solution: Add validation step that checks credentials exist - Fails early with clear error if secrets missing - Shows how to configure in repo settings - Uses direct secret injection (not via env vars) - Isolates docker config to /tmp/docker-config Result: CI will fail fast with actionable error if credentials missing