fix(antigravity): trigger failover retry on empty stream caused by MALFORMED_FUNCTION_CALL

backend/internal/pkg/antigravity/stream_transformer.go

@@ -40,6 +40,7 @@ type StreamingProcessor struct {
 	outputTokens      int
 	cacheReadTokens   int
 	imageOutputTokens int
+	hasContent        bool
 }
 
 // NewStreamingProcessor 创建流式响应处理器
@@ -175,6 +176,11 @@ func (p *StreamingProcessor) MessageStartSent() bool {
 	return p.messageStartSent
 }
 
+// HasContent reports whether any substantive text, thinking, or tool calls were emitted.
+func (p *StreamingProcessor) HasContent() bool {
+	return p.hasContent
+}
+
 // emitMessageStart 发送 message_start 事件
 func (p *StreamingProcessor) emitMessageStart(v1Resp *V1InternalResponse) []byte {
 	if p.messageStartSent {
@@ -296,6 +302,7 @@ func (p *StreamingProcessor) processThinking(text, signature string) []byte {
 	}
 
 	if text != "" {
+		p.hasContent = true
 		_, _ = result.Write(p.emitDelta("thinking_delta", map[string]any{
 			"thinking": text,
 		}))
@@ -350,6 +357,7 @@ func (p *StreamingProcessor) processText(text, signature string) []byte {
 		}))
 	}
 
+	p.hasContent = true
 	_, _ = result.Write(p.emitDelta("text_delta", map[string]any{
 		"text": text,
 	}))
@@ -362,6 +370,7 @@ func (p *StreamingProcessor) processFunctionCall(fc *GeminiFunctionCall, signatu
 	var result bytes.Buffer
 
 	p.usedTool = true
+	p.hasContent = true
 
 	toolID := fc.ID
 	if toolID == "" {

backend/internal/service/antigravity_gateway_compat_stream.go

@@ -144,12 +144,15 @@ func (s *antigravityCompatStreamSession) hasMeaningfulData() bool {
 	return s.meaningfulData
 }
 
-func (s *antigravityCompatStreamSession) finish() *antigravityStreamResult {
+func (s *antigravityCompatStreamSession) finish() (*antigravityStreamResult, error) {
 	finalEvents, usage := s.processor.Finish()
 	mergeAntigravityCompatUsage(s.usage, usage)
 	s.consumeClaudeEvents(finalEvents)
+	if !s.hasMeaningfulData() && !s.writer.Disconnected() {
+		return nil, antigravityCompatEmptyStreamError()
+	}
 	s.adapter.Finalize(s.writer)
-	return s.result(s.writer.Disconnected())
+	return s.result(s.writer.Disconnected()), nil
 }
 
 func (s *antigravityCompatStreamSession) collectResult(clientDisconnect bool) *antigravityStreamResult {
@@ -236,8 +239,7 @@ func isMeaningfulAntigravityCompatEvent(event *apicompat.AnthropicStreamEvent) b
 		return delta.Text != "" ||
 			delta.PartialJSON != "" ||
 			delta.Thinking != "" ||
-			delta.Signature != "" ||
-			delta.StopReason != ""
+			delta.Signature != ""
 	}
 	return false
 }
@@ -295,7 +297,7 @@ func (s *AntigravityGatewayService) handleAntigravityCompatStream(
 				if !session.hasMeaningfulData() && !writer.Disconnected() {
 					return nil, antigravityCompatEmptyStreamError()
 				}
-				return session.finish(), nil
+				return session.finish()
 			}
 			if event.err != nil {
 				return s.handleAntigravityCompatReadError(c, session, event.err, maxLineSize, prefix)