fix(protocol): align terminal receipt conformance

tools/go-conformance/main.go

@@ -270,12 +270,16 @@ func classifyGatewayFeedback(encoded string) string {
 				return "valid"
 			}
 			return "invalid:field"
+		case 3:
+			if len(body) == 0 {
+				return "valid"
+			}
 		default:
 			return "invalid:type"
 		}
 		return "invalid:length"
 	}
-	if kind == 1 || kind == 2 {
+	if kind == 1 || kind == 2 || kind == 3 {
 		return "invalid:direction"
 	}
 	switch kind {