Add configured source validation and inspection

internal/app/run.go

@@ -310,6 +310,9 @@ func sshWarnings(pipeline config.Pipeline) []OutputWarning {
 }
 
 func writeWarnings(w io.Writer, warnings []OutputWarning) error {
+	if w == nil {
+		return nil
+	}
 	for _, warning := range warnings {
 		if _, err := fmt.Fprintf(w, "Warning: %s\n", warning.Message); err != nil {
 			return err