ax(node): add missing _Bad and _Ugly test variants for TestMessage_NewMessage

AX Principle 10 (CLI tests as artifact validation) requires all three
test categories — Good, Bad, Ugly — to be mandatory. TestMessage_NewMessage
had only _Good; add _Bad (unmarshalable payload returns error) and _Ugly
(empty From/To fields succeed and produce a valid message ID).

Co-Authored-By: Charon <charon@lethean.io>

pkg/node/message_test.go

@@ -60,6 +60,37 @@ func TestMessage_NewMessage_Good(t *testing.T) {
 	})
 }
 
+// TestMessage_NewMessage_Bad verifies that NewMessage returns an error when the payload cannot be marshalled.
+//
+//	_, err := NewMessage(MsgPing, "sender", "receiver", make(chan int))
+//	if err == nil { t.Error("expected error for unmarshalable payload") }
+func TestMessage_NewMessage_Bad(t *testing.T) {
+	// A channel cannot be marshalled to JSON — NewMessage must propagate the error.
+	_, err := NewMessage(MsgPing, "sender-id", "receiver-id", make(chan int))
+	if err == nil {
+		t.Error("expected error when payload cannot be marshalled, got nil")
+	}
+}
+
+// TestMessage_NewMessage_Ugly verifies that NewMessage succeeds with empty From/To fields.
+//
+//	msg, err := NewMessage(MsgPing, "", "", nil)
+//	if err != nil { t.Fatalf("unexpected error: %v", err) }
+//	if msg.ID == "" { t.Error("message ID should not be empty even with empty from/to") }
+func TestMessage_NewMessage_Ugly(t *testing.T) {
+	// Empty From/To should not cause an error — callers control routing.
+	msg, err := NewMessage(MsgPing, "", "", nil)
+	if err != nil {
+		t.Fatalf("unexpected error with empty from/to: %v", err)
+	}
+	if msg.ID == "" {
+		t.Error("message ID should not be empty even with empty from/to")
+	}
+	if msg.Type != MsgPing {
+		t.Errorf("expected type MsgPing, got %s", msg.Type)
+	}
+}
+
 func TestMessage_Reply_Good(t *testing.T) {
 	original, _ := NewMessage(MsgPing, "sender", "receiver", PingPayload{SentAt: 12345})