perf: batch gateway submits and isolate callbacks

gateway/internal/upstream/manager.go

@@ -23,6 +23,7 @@ const (
 
 type Manager struct {
 	APIBaseURL             string
+	EventAPIBaseURL        string
 	HTTPClient             *http.Client
 	SubmitSegmentPublisher SubmitSegmentPublisher
 
@@ -170,11 +171,15 @@ func (m *Manager) ConnectionCounts() (desired int, connected int) {
 }
 
 func (m *Manager) newConnectionPool(channelID string, connectionID string, config queue.UpstreamConfig) *connectionPool {
+	eventAPIBaseURL := m.EventAPIBaseURL
+	if eventAPIBaseURL == "" {
+		eventAPIBaseURL = m.APIBaseURL
+	}
 	return &connectionPool{
 		channelID:    channelID,
 		connectionID: connectionID,
 		config:       config,
-		apiBaseURL:   m.APIBaseURL,
+		apiBaseURL:   eventAPIBaseURL,
 		httpClient:   m.HTTPClient,
 		reporter: func(ctx context.Context, state ConnectionState) error {
 			return m.post(ctx, "/admin/gateway/connections", state)

gateway/internal/upstream/pool_test.go

@@ -85,6 +85,17 @@ func TestNormalizeUpstreamConfigDefaults(t *testing.T) {
 	}
 }
 
+func TestManagerSeparatesConnectionStateAndSupplierEventAPIs(t *testing.T) {
+	manager := &Manager{APIBaseURL: "http://main-api/api", EventAPIBaseURL: "http://callback-api/api"}
+	pool := manager.newConnectionPool("channel-1", "channel-1:primary", queue.UpstreamConfig{DesiredConnections: 1})
+	if pool.apiBaseURL != manager.EventAPIBaseURL {
+		t.Fatalf("supplier events must use callback API, got %q", pool.apiBaseURL)
+	}
+	if manager.APIBaseURL == pool.apiBaseURL {
+		t.Fatal("connection-state control API must remain separate from supplier events")
+	}
+}
+
 func queueUpstreamConfigForTest() queue.UpstreamConfig {
 	return queue.UpstreamConfig{
 		GatewayHost:    "127.0.0.1",