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 {

tools/native_conformance.rs

@@ -143,10 +143,12 @@ fn classify_gateway_feedback(encoded: &str) -> &'static str {
             1 => "invalid:length",
             2 if valid_fec_status(body) => "valid",
             2 => "invalid:field",
+            3 if body.is_empty() => "valid",
+            3 => "invalid:length",
             _ => "invalid:type",
         };
     }
-    if kind == 1 || kind == 2 {
+    if kind == 1 || kind == 2 || kind == 3 {
         return "invalid:direction";
     }
     match kind {

tools/native_conformance.swift

@@ -101,10 +101,11 @@ func classifyGatewayFeedback(_ encoded: String) -> String {
         case 1: return body.isEmpty ? "valid" : "invalid:length"
         case 2:
             return validFECStatus(body) ? "valid" : "invalid:field"
+        case 3: return body.isEmpty ? "valid" : "invalid:length"
         default: return "invalid:type"
         }
     }
-    if kind == 1 || kind == 2 { return "invalid:direction" }
+    if kind == 1 || kind == 2 || kind == 3 { return "invalid:direction" }
     switch kind {
     case 0x10: return body.count == 4 ? "valid" : "invalid:length"
     case 0x11:

tools/validate_gateway_envelopes.py

@@ -59,8 +59,10 @@ def classify_feedback(raw: bytes) -> str:
             return "valid" if not body else "invalid:length"
         if kind == 2:
             return "valid" if valid_fec_status(body) else "invalid:field"
+        if kind == 3:
+            return "valid" if not body else "invalid:length"
         return "invalid:type"
-    if kind in (1, 2):
+    if kind in (1, 2, 3):
         return "invalid:direction"
     if kind == 0x10:
         return "valid" if len(body) == 4 else "invalid:length"