diff --git a/backend/internal/service/antigravity_gateway_service_test.go b/backend/internal/service/antigravity_gateway_service_test.go
index dfca59619c..79ce35f596 100644
--- a/backend/internal/service/antigravity_gateway_service_test.go
+++ b/backend/internal/service/antigravity_gateway_service_test.go
@@ -1387,6 +1387,49 @@ func TestHandleClaudeStreamingResponse_NormalComplete(t *testing.T) {
 
 // TestHandleGeminiStreamingResponse_ThoughtsTokenCount
 // 验证：Gemini 流式转发时 thoughtsTokenCount 被计入 OutputTokens
+// 回归：上游事件之间的空分隔行不能再透传，否则下游看到的是 "data: ...\n\n\n"。
+// google-genai Go SDK 按 "\n\n" 切事件，多出的 "\n" 会让第二个事件的前缀变成
+// "\ndata" 而报 invalid stream chunk（Antigravity CLI 每条流都在第二个事件中断）。
+func TestHandleGeminiStreamingResponse_EventSeparatorIsExactlyOneBlankLine(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	svc := newAntigravityTestService(&config.Config{
+		Gateway: config.GatewayConfig{MaxLineSize: defaultMaxLineSize},
+	})
+
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/", nil)
+
+	pr, pw := io.Pipe()
+	resp := &http.Response{StatusCode: http.StatusOK, Body: pr, Header: http.Header{}}
+
+	first := `{"candidates":[{"content":{"role":"model","parts":[{"text":"Hello"}]}}],"usageMetadata":{"promptTokenCount":10,"candidatesTokenCount":3}}`
+	second := `{"candidates":[{"content":{"role":"model","parts":[{"thoughtSignature":"sig","text":""}]},"finishReason":"STOP"}],"usageMetadata":{"promptTokenCount":10,"candidatesTokenCount":3,"thoughtsTokenCount":5}}`
+
+	go func() {
+		defer func() { _ = pw.Close() }()
+		// 上游原样：每个 data 行后跟一个空分隔行（第二个事件用 CRLF，覆盖两种换行）
+		fmt.Fprintf(pw, "data: %s\n\n", first)
+		fmt.Fprintf(pw, "data: %s\r\n\r\n", second)
+	}()
+
+	result, err := svc.handleGeminiStreamingResponse(c, resp, time.Now())
+	_ = pr.Close()
+
+	require.NoError(t, err)
+	require.NotNil(t, result)
+
+	body := rec.Body.String()
+	require.Equal(t, "data: "+first+"\n\ndata: "+second+"\n\n", body)
+	require.NotContains(t, body, "\n\n\n", "events must be separated by exactly one blank line")
+
+	// 模拟 google-genai 的切帧方式：按 "\n\n" 切，每个非空 token 都必须以 "data" 为前缀
+	for _, token := range strings.Split(strings.TrimSuffix(body, "\n\n"), "\n\n") {
+		prefix, _, _ := strings.Cut(token, ":")
+		require.Equal(t, "data", prefix, "token %q would be rejected by a \\n\\n-delimited SSE parser", token)
+	}
+}
+
 func TestHandleGeminiStreamingResponse_ThoughtsTokenCount(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	svc := newAntigravityTestService(&config.Config{
diff --git a/backend/internal/service/antigravity_gateway_streaming.go b/backend/internal/service/antigravity_gateway_streaming.go
index 002543f9ec..5922554207 100644
--- a/backend/internal/service/antigravity_gateway_streaming.go
+++ b/backend/internal/service/antigravity_gateway_streaming.go
@@ -288,6 +288,14 @@ func (s *AntigravityGatewayService) handleGeminiStreamingResponse(c *gin.Context
 				continue
 			}
 
+			// 上游每个 data 事件后面跟一个空行作为事件分隔。上面已经把 data 行写成
+			// "data: ...\n\n"，若再把这个空行透传出去，事件之间就会变成 "\n\n\n"。
+			// google-genai 的 Go SDK（Antigravity CLI 在用）按 "\n\n" 切事件，多出的
+			// "\n" 会粘到下一个事件开头，前缀变成 "\ndata" 而被判成 invalid stream chunk。
+			if trimmed == "" {
+				continue
+			}
+
 			cw.Fprintf("%s\n", line)
 
 		case <-intervalCh: