feat: add validation for Claude streaming responses

- Implemented `validateClaudeStreamingResponse` to ensure upstream streaming data integrity.
- Added new tests to verify response validation, including empty streams, error events, incomplete streams, and valid streams.
- Integrated validation logic into the Claude executor's streaming handler, returning detailed errors for malformed upstream data.

Fixed: #2193

internal/runtime/executor/claude_executor.go

@@ -285,6 +285,10 @@ func (e *ClaudeExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, r
 	}
 	helps.AppendAPIResponseChunk(ctx, e.cfg, data)
 	if stream {
+		if errValidate := validateClaudeStreamingResponse(data); errValidate != nil {
+			helps.RecordAPIResponseError(ctx, e.cfg, errValidate)
+			return resp, errValidate
+		}
 		lines := bytes.Split(data, []byte("\n"))
 		for _, line := range lines {
 			if detail, ok := helps.ParseClaudeStreamUsage(line); ok {
@@ -533,6 +537,64 @@ func (e *ClaudeExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.A
 	return &cliproxyexecutor.StreamResult{Headers: httpResp.Header.Clone(), Chunks: out}, nil
 }
 
+func validateClaudeStreamingResponse(data []byte) error {
+	scanner := bufio.NewScanner(bytes.NewReader(data))
+	scanner.Buffer(nil, 52_428_800)
+
+	hasData := false
+	hasMessageStart := false
+	hasMessageDelta := false
+
+	for scanner.Scan() {
+		line := bytes.TrimSpace(scanner.Bytes())
+		if len(line) == 0 || !bytes.HasPrefix(line, []byte("data:")) {
+			continue
+		}
+		payload := bytes.TrimSpace(line[len("data:"):])
+		if len(payload) == 0 || bytes.Equal(payload, []byte("[DONE]")) {
+			continue
+		}
+		hasData = true
+		if !gjson.ValidBytes(payload) {
+			return statusErr{code: http.StatusBadGateway, msg: "claude executor: upstream returned malformed stream data"}
+		}
+
+		root := gjson.ParseBytes(payload)
+		switch root.Get("type").String() {
+		case "error":
+			message := strings.TrimSpace(root.Get("error.message").String())
+			if message == "" {
+				message = strings.TrimSpace(root.Get("error.type").String())
+			}
+			if message == "" {
+				message = "unknown upstream error"
+			}
+			return statusErr{code: http.StatusBadGateway, msg: "claude executor: upstream returned error event: " + message}
+		case "message_start":
+			message := root.Get("message")
+			if strings.TrimSpace(message.Get("id").String()) == "" || strings.TrimSpace(message.Get("model").String()) == "" {
+				return statusErr{code: http.StatusBadGateway, msg: "claude executor: upstream stream message_start is missing id or model"}
+			}
+			hasMessageStart = true
+		case "message_delta":
+			hasMessageDelta = true
+		}
+	}
+	if errScan := scanner.Err(); errScan != nil {
+		return errScan
+	}
+	if !hasData {
+		return statusErr{code: http.StatusBadGateway, msg: "claude executor: upstream returned empty stream response"}
+	}
+	if !hasMessageStart {
+		return statusErr{code: http.StatusBadGateway, msg: "claude executor: upstream stream response is missing message_start"}
+	}
+	if !hasMessageDelta {
+		return statusErr{code: http.StatusBadGateway, msg: "claude executor: upstream stream response ended before message completion"}
+	}
+	return nil
+}
+
 func (e *ClaudeExecutor) CountTokens(ctx context.Context, auth *cliproxyauth.Auth, req cliproxyexecutor.Request, opts cliproxyexecutor.Options) (cliproxyexecutor.Response, error) {
 	baseModel := thinking.ParseSuffix(req.Model).ModelName