fix(cmpp): preserve inbound window after message registration

gateway/internal/inbound/server_test.go

@@ -346,6 +346,21 @@ func TestBoundedSubmitWindowAndAggregateSlotSnapshot(t *testing.T) {
 	if configured != 48 || inFlight != 4 {
 		t.Fatalf("slot snapshot configured=%d in_flight=%d, want 48/4", configured, inFlight)
 	}
+
+	conn := &cmpp.Conn{}
+	counter := &atomic.Int64{}
+	counter.Store(2)
+	rememberDownstream(downstreamSession{
+		messageID: "MSG-WINDOW-SNAPSHOT", account: "100030", conn: conn,
+		windowSize: 32, submitInFlight: counter,
+	})
+	if got := submitWindowByConn(conn); got != 32 {
+		t.Fatalf("message registration replaced connection window with %d, want 32", got)
+	}
+	configured, inFlight = SubmitSlotSnapshot()
+	if configured != 80 || inFlight != 6 {
+		t.Fatalf("post-message slot snapshot configured=%d in_flight=%d, want 80/6", configured, inFlight)
+	}
 }
 
 func TestDecodeInboundLongMessageStripsConcatUDHBeforeUCS2Decode(t *testing.T) {

gateway/internal/inbound/submit.go

@@ -169,6 +169,8 @@ func (s Server) handleSubmit(response *cmpp.Response, packet *cmpp.Packet, logge
 			applicationID:  result.ApplicationID,
 			enterpriseCode: session.enterpriseCode,
 			protocol:       clientProtocol,
+			windowSize:     session.windowSize,
+			submitInFlight: session.submitInFlight,
 			srcID:          strings.TrimSpace(req.srcID),
 			phoneNumber:    acceptedPhone,
 			gatewayMsgID:   gatewayMsgID,