fix: preserve SSE event boundaries for Responses streams

sdk/api/handlers/openai/openai_responses_handlers.go

@@ -10,6 +10,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"io"
 	"net/http"
 
 	"github.com/gin-gonic/gin"
@@ -21,6 +22,21 @@ import (
 	"github.com/tidwall/sjson"
 )
 
+func writeResponsesSSEChunk(w io.Writer, chunk []byte) {
+	if w == nil || len(chunk) == 0 {
+		return
+	}
+	_, _ = w.Write(chunk)
+	switch {
+	case bytes.HasSuffix(chunk, []byte("\n\n")):
+		return
+	case bytes.HasSuffix(chunk, []byte("\n")):
+		_, _ = w.Write([]byte("\n"))
+	default:
+		_, _ = w.Write([]byte("\n\n"))
+	}
+}
+
 // OpenAIResponsesAPIHandler contains the handlers for OpenAIResponses API endpoints.
 // It holds a pool of clients to interact with the backend service.
 type OpenAIResponsesAPIHandler struct {
@@ -230,11 +246,7 @@ func (h *OpenAIResponsesAPIHandler) handleStreamingResponse(c *gin.Context, rawJ
 			handlers.WriteUpstreamHeaders(c.Writer.Header(), upstreamHeaders)
 
 			// Write first chunk logic (matching forwardResponsesStream)
-			if bytes.HasPrefix(chunk, []byte("event:")) {
-				_, _ = c.Writer.Write([]byte("\n"))
-			}
-			_, _ = c.Writer.Write(chunk)
-			_, _ = c.Writer.Write([]byte("\n"))
+			writeResponsesSSEChunk(c.Writer, chunk)
 			flusher.Flush()
 
 			// Continue
@@ -247,11 +259,7 @@ func (h *OpenAIResponsesAPIHandler) handleStreamingResponse(c *gin.Context, rawJ
 func (h *OpenAIResponsesAPIHandler) forwardResponsesStream(c *gin.Context, flusher http.Flusher, cancel func(error), data <-chan []byte, errs <-chan *interfaces.ErrorMessage) {
 	h.ForwardStream(c, flusher, cancel, data, errs, handlers.StreamForwardOptions{
 		WriteChunk: func(chunk []byte) {
-			if bytes.HasPrefix(chunk, []byte("event:")) {
-				_, _ = c.Writer.Write([]byte("\n"))
-			}
-			_, _ = c.Writer.Write(chunk)
-			_, _ = c.Writer.Write([]byte("\n"))
+			writeResponsesSSEChunk(c.Writer, chunk)
 		},
 		WriteTerminalError: func(errMsg *interfaces.ErrorMessage) {
 			if errMsg == nil {