feat: support Responses to Chat (#5787)

* fix(openai): harden Chat-to-Responses compatibility

Add a shared Responses-to-Chat stream state machine and use it from the OpenAI relay path. Preserve assistant text alongside tool calls, bind tool argument deltas by output_index, map incomplete finish reasons, support reasoning/custom tool events, and buffer upstream SSE for non-stream Chat clients.

Add deterministic service tests and relay SSE tests for the conversion path.

Related to #5745.

* refactor: rename openaicompat to relayconvert for improved clarity

* feat(gemini): support responses request conversion

* feat: add responses to chat conversion support

* fix: harden responses chat conversion edge cases

relay/channel/advancedcustom/adaptor.go

@@ -104,10 +104,18 @@ func (a *Adaptor) ConvertOpenAIResponsesRequest(c *gin.Context, info *relaycommo
 	if err != nil {
 		return nil, err
 	}
-	if converter != dto.AdvancedCustomConverterNone {
+	switch converter {
+	case dto.AdvancedCustomConverterNone:
+		return a.convertOpenAICompatibleResponsesRequest(c, info, request)
+	case dto.AdvancedCustomConverterOpenAIResponsesToOpenAIChatCompletions:
+		chatReq, err := service.ResponsesRequestToChatCompletionsRequest(&request)
+		if err != nil {
+			return nil, err
+		}
+		return a.convertOpenAICompatibleRequest(c, info, chatReq)
+	default:
 		return nil, fmt.Errorf("converter %q does not support OpenAI Responses requests", converter)
 	}
-	return a.convertOpenAICompatibleResponsesRequest(c, info, request)
 }
 
 func (a *Adaptor) ConvertEmbeddingRequest(c *gin.Context, info *relaycommon.RelayInfo, request dto.EmbeddingRequest) (any, error) {
@@ -221,6 +229,11 @@ func (a *Adaptor) DoResponse(c *gin.Context, resp *http.Response, info *relaycom
 			return openai.OaiResponsesToChatStreamHandler(c, info, resp)
 		}
 		return openai.OaiResponsesToChatHandler(c, info, resp)
+	case dto.AdvancedCustomConverterOpenAIResponsesToOpenAIChatCompletions:
+		if info.IsStream {
+			return openai.OaiChatToResponsesStreamHandler(c, info, resp)
+		}
+		return openai.OaiChatToResponsesHandler(c, info, resp)
 	default:
 		return nil, types.NewOpenAIError(fmt.Errorf("unsupported advanced custom converter: %s", a.converter), types.ErrorCodeInvalidRequest, http.StatusBadRequest, types.ErrOptionWithSkipRetry())
 	}

relay/channel/advancedcustom/adaptor_test.go

@@ -6,6 +6,7 @@ import (
 	"net/url"
 	"testing"
 
+	"github.com/QuantumNous/new-api/common"
 	"github.com/QuantumNous/new-api/constant"
 	"github.com/QuantumNous/new-api/dto"
 	relaycommon "github.com/QuantumNous/new-api/relay/common"
@@ -279,6 +280,44 @@ func TestAdaptorMatchesGeminiIncomingPathTemplate(t *testing.T) {
 	}
 }
 
+func TestAdaptorConvertsResponsesRequestToOpenAIChatUpstream(t *testing.T) {
+	adaptor := &Adaptor{}
+	info := advancedCustomRelayInfo(&dto.AdvancedCustomConfig{
+		Routes: []dto.AdvancedCustomRoute{
+			{
+				IncomingPath: "/v1/responses",
+				UpstreamPath: "/v1/chat/completions",
+				Converter:    dto.AdvancedCustomConverterOpenAIResponsesToOpenAIChatCompletions,
+			},
+		},
+	})
+	info.RelayMode = relayconstant.RelayModeResponses
+	info.RequestURLPath = "/v1/responses"
+	c := advancedCustomGinContext("/v1/responses")
+
+	converted, err := adaptor.ConvertOpenAIResponsesRequest(c, info, dto.OpenAIResponsesRequest{
+		Model:        "gpt-test",
+		Instructions: mustAdvancedCustomRawMessage(t, "system rules"),
+		Input:        mustAdvancedCustomRawMessage(t, "hello"),
+	})
+	require.NoError(t, err)
+
+	chatReq, ok := converted.(*dto.GeneralOpenAIRequest)
+	require.True(t, ok)
+	assert.Equal(t, "gpt-test", chatReq.Model)
+	require.Len(t, chatReq.Messages, 2)
+	assert.Equal(t, "system", chatReq.Messages[0].Role)
+	assert.Equal(t, "system rules", chatReq.Messages[0].StringContent())
+	assert.Equal(t, "user", chatReq.Messages[1].Role)
+	assert.Equal(t, "hello", chatReq.Messages[1].StringContent())
+
+	requestURL, err := adaptor.GetRequestURL(info)
+	require.NoError(t, err)
+	parsedURL, err := url.Parse(requestURL)
+	require.NoError(t, err)
+	assert.Equal(t, "/v1/chat/completions", parsedURL.Path)
+}
+
 func advancedCustomRelayInfo(config *dto.AdvancedCustomConfig) *relaycommon.RelayInfo {
 	return &relaycommon.RelayInfo{
 		RelayFormat:    types.RelayFormatOpenAI,
@@ -302,3 +341,10 @@ func advancedCustomGinContext(path string) *gin.Context {
 	c.Request.Header.Set("Content-Type", "application/json")
 	return c
 }
+
+func mustAdvancedCustomRawMessage(t *testing.T, value any) []byte {
+	t.Helper()
+	raw, err := common.Marshal(value)
+	require.NoError(t, err)
+	return raw
+}