feat: add Responses API compatibility

apps/api/internal/httpapi/streaming.go

@@ -28,6 +28,8 @@ type compatibleStreamWriter struct {
 	sentRole          bool
 	sentFinish        bool
 	sentUsage         bool
+	responseSequence  int
+	sentResponseDone  bool
 }
 
 func newCompatibleStreamWriter(kind string, model string, includeUsage bool) *compatibleStreamWriter {
@@ -42,6 +44,19 @@ func newCompatibleStreamWriter(kind string, model string, includeUsage bool) *co
 
 func (s *compatibleStreamWriter) writeDelta(w http.ResponseWriter, event clients.StreamDeltaEvent) {
 	if s.kind == "responses" {
+		if event.Event != nil {
+			eventType, _ := event.Event["type"].(string)
+			if eventType != "" {
+				if sequence := intFromStreamValue(event.Event["sequence_number"]); sequence >= s.responseSequence {
+					s.responseSequence = sequence + 1
+				}
+				if eventType == "response.completed" {
+					s.sentResponseDone = true
+				}
+				sendSSE(w, eventType, event.Event)
+				return
+			}
+		}
 		if event.Text != "" {
 			sendSSE(w, "response.output_text.delta", map[string]any{"type": "response.output_text.delta", "delta": event.Text})
 		}
@@ -67,7 +82,11 @@ func (s *compatibleStreamWriter) writeDelta(w http.ResponseWriter, event clients
 
 func (s *compatibleStreamWriter) writeDone(w http.ResponseWriter, output map[string]any) {
 	if s.kind == "responses" {
-		sendSSE(w, "response.completed", map[string]any{"type": "response.completed", "response": output})
+		if s.sentResponseDone {
+			return
+		}
+		sendSSE(w, "response.completed", map[string]any{"type": "response.completed", "sequence_number": s.responseSequence, "response": output})
+		s.sentResponseDone = true
 		return
 	}
 	s.captureOutputMetadata(output)
@@ -88,6 +107,19 @@ func (s *compatibleStreamWriter) writeDone(w http.ResponseWriter, output map[str
 	s.writeDoneMarker(w)
 }
 
+func intFromStreamValue(value any) int {
+	switch typed := value.(type) {
+	case int:
+		return typed
+	case int64:
+		return int(typed)
+	case float64:
+		return int(typed)
+	default:
+		return -1
+	}
+}
+
 func (s *compatibleStreamWriter) writeChatChunk(w http.ResponseWriter, chunk map[string]any) {
 	chunk = clients.NormalizeChatCompletionStreamEvent(chunk)
 	s.captureChunkMetadata(chunk)