fix: harden channel retry attribution and operations UI

gateway/internal/queue/messages.go

@@ -79,6 +79,7 @@ type Retry struct {
 
 type SubmitResult struct {
 	Envelope
+	SubmitID         string                `json:"submitId"`
 	SequenceID       uint32                `json:"sequenceId"`
 	GatewayMessageID string                `json:"gatewayMessageId"`
 	SubmitStatus     string                `json:"submitStatus"`

gateway/internal/queue/messages_test.go

@@ -67,3 +67,20 @@ func TestSubmitCommandUnmarshalsQueuePriority(t *testing.T) {
 		t.Fatalf("unexpected extension digits: %d", command.CMPP.ExtensionDigits)
 	}
 }
+
+func TestSubmitResultMarshalsSubmitID(t *testing.T) {
+	payload, err := json.Marshal(SubmitResult{SubmitID: "submit-1"})
+	if err != nil {
+		t.Fatalf("marshal submit result: %v", err)
+	}
+	if string(payload) == "" || !json.Valid(payload) {
+		t.Fatalf("invalid submit result JSON: %s", payload)
+	}
+	var decoded map[string]any
+	if err := json.Unmarshal(payload, &decoded); err != nil {
+		t.Fatalf("unmarshal submit result: %v", err)
+	}
+	if decoded["submitId"] != "submit-1" {
+		t.Fatalf("submitId = %v, want submit-1", decoded["submitId"])
+	}
+}