perf(cmpp): decouple supplier result callbacks

gateway/internal/upstream/manager.go

@@ -22,13 +22,21 @@ const (
 )
 
 type Manager struct {
-	APIBaseURL string
-	HTTPClient *http.Client
+	APIBaseURL             string
+	HTTPClient             *http.Client
+	SubmitSegmentPublisher SubmitSegmentPublisher
 
 	mu    sync.Mutex
 	conns map[string]*connectionPool
 }
 
+// SubmitSegmentPublisher persists each supplier response before the next long-message
+// segment is sent. The boundary is intentionally storage-only: HTTP callbacks belong to
+// the result Outbox worker and must not consume a supplier Submit window slot.
+type SubmitSegmentPublisher interface {
+	PublishSubmitSegment(context.Context, queue.SubmitCommand, queue.SubmitSegmentResult) error
+}
+
 type ConnectionState struct {
 	ChannelID              string `json:"channelId"`
 	ConnectionID           string `json:"connectionId"`