feat(protocol): freeze M4 native session RC6 contract

tools/validate_gateway_envelopes.py

@@ -44,6 +44,10 @@ def classify_input(raw: bytes) -> str:
         return "valid" if width and height and x < width and y < height else "invalid:field"
     if kind == 7:
         return "valid" if len(body) == 4 else "invalid:length"
+    if kind == 8:
+        if len(body) != 8:
+            return "invalid:length"
+        return "valid" if body[0] <= 15 and body[3] <= 3 else "invalid:field"
     return "invalid:kind"
 
 
@@ -68,6 +72,14 @@ def classify_feedback(raw: bytes) -> str:
             return "valid" if valid_fec_status(body) else "invalid:field"
         if kind == 3:
             return "valid" if not body else "invalid:length"
+        if kind == 4:
+            if len(body) != 24:
+                return "invalid:length"
+            return "valid" if any(body[:16]) and int.from_bytes(body[16:24], "big") > 0 else "invalid:field"
+        if kind == 5:
+            if len(body) != 16:
+                return "invalid:length"
+            return "valid" if any(body) else "invalid:field"
         return "invalid:type"
     if kind in (1, 2, 3):
         return "invalid:direction"