feat: improve OpenAI messages compatibility for Claude Code

backend/internal/service/openai_oauth_passthrough_test.go

@@ -25,9 +25,12 @@ func f64p(v float64) *float64 { return &v }
 type httpUpstreamRecorder struct {
 	lastReq  *http.Request
 	lastBody []byte
+	requests []*http.Request
+	bodies   [][]byte
 
-	resp *http.Response
-	err  error
+	resp      *http.Response
+	responses []*http.Response
+	err       error
 }
 
 func (u *httpUpstreamRecorder) Do(req *http.Request, proxyURL string, accountID int64, accountConcurrency int) (*http.Response, error) {
@@ -35,12 +38,19 @@ func (u *httpUpstreamRecorder) Do(req *http.Request, proxyURL string, accountID
 	if req != nil && req.Body != nil {
 		b, _ := io.ReadAll(req.Body)
 		u.lastBody = b
+		u.bodies = append(u.bodies, append([]byte(nil), b...))
 		_ = req.Body.Close()
 		req.Body = io.NopCloser(bytes.NewReader(b))
 	}
+	u.requests = append(u.requests, req)
 	if u.err != nil {
 		return nil, u.err
 	}
+	if len(u.responses) > 0 {
+		resp := u.responses[0]
+		u.responses = u.responses[1:]
+		return resp, nil
+	}
 	return u.resp, nil
 }
 
@@ -91,6 +101,50 @@ func TestOpenAIGatewayService_ResponsesUnknownModelDoesNotFallbackToGPT54(t *tes
 	require.True(t, rec.Code >= http.StatusBadRequest)
 }
 
+func TestOpenAIGatewayService_OAuthMessagesBridgeDoesNotInjectDefaultInstructions(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	originalBody := []byte(`{"model":"gpt-5.5","stream":true,"prompt_cache_key":"anthropic-metadata-session-1","input":[{"type":"message","role":"developer","content":[{"type":"input_text","text":"<sub2api-claude-code-todo-guard>"}]},{"type":"message","role":"user","content":"hello"}]}`)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", bytes.NewReader(originalBody))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	upstream := &httpUpstreamRecorder{resp: &http.Response{
+		StatusCode: http.StatusBadRequest,
+		Header:     http.Header{"Content-Type": []string{"application/json"}, "x-request-id": []string{"rid_bridge"}},
+		Body:       io.NopCloser(strings.NewReader(`{"error":{"type":"invalid_request_error","message":"bridge stop"}}`)),
+	}}
+	svc := &OpenAIGatewayService{
+		cfg:          &config.Config{},
+		httpUpstream: upstream,
+	}
+	account := &Account{
+		ID:          123,
+		Name:        "acc",
+		Platform:    PlatformOpenAI,
+		Type:        AccountTypeOAuth,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"access_token":       "oauth-token",
+			"chatgpt_account_id": "chatgpt-acc",
+		},
+		Status:      StatusActive,
+		Schedulable: true,
+	}
+
+	result, err := svc.Forward(context.Background(), c, account, originalBody)
+	require.Error(t, err)
+	require.Nil(t, result)
+	require.NotNil(t, upstream.lastReq)
+	require.Equal(t, "", gjson.GetBytes(upstream.lastBody, "instructions").String())
+	require.False(t, gjson.GetBytes(upstream.lastBody, "prompt_cache_key").Exists())
+	require.NotEmpty(t, upstream.lastReq.Header.Get("Session_Id"))
+	require.Empty(t, upstream.lastReq.Header.Get("Conversation_Id"))
+	require.Empty(t, upstream.lastReq.Header.Get("OpenAI-Beta"))
+	require.Empty(t, upstream.lastReq.Header.Get("originator"))
+}
+
 type openAIPassthroughFailoverRepo struct {
 	stubOpenAIAccountRepo
 	rateLimitCalls []time.Time