fix(openai): emit valid responses stream error chunks

When /v1/responses streaming fails after headers are sent, we now emit a type=error chunk instead of an HTTP-style {error:{...}} payload, preventing AI SDK chunk validation errors.

sdk/api/handlers/openai/openai_responses_handlers.go

@@ -265,8 +265,8 @@ func (h *OpenAIResponsesAPIHandler) forwardResponsesStream(c *gin.Context, flush
 			if errMsg.Error != nil && errMsg.Error.Error() != "" {
 				errText = errMsg.Error.Error()
 			}
-			body := handlers.BuildErrorResponseBody(status, errText)
+			chunk := handlers.BuildOpenAIResponsesStreamErrorChunk(status, errText, 0)
-			_, _ = fmt.Fprintf(c.Writer, "\nevent: error\ndata: %s\n\n", string(body))
+			_, _ = fmt.Fprintf(c.Writer, "\nevent: error\ndata: %s\n\n", string(chunk))
 		},
 		WriteDone: func() {
 			_, _ = c.Writer.Write([]byte("\n"))

sdk/api/handlers/openai/openai_responses_handlers_stream_error_test.go

@@ -0,0 +1,43 @@
+package openai
+
+import (
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/interfaces"
+	"github.com/router-for-me/CLIProxyAPI/v6/sdk/api/handlers"
+	sdkconfig "github.com/router-for-me/CLIProxyAPI/v6/sdk/config"
+)
+
+func TestForwardResponsesStreamTerminalErrorUsesResponsesErrorChunk(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	base := handlers.NewBaseAPIHandlers(&sdkconfig.SDKConfig{}, nil)
+	h := NewOpenAIResponsesAPIHandler(base)
+
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", nil)
+
+	flusher, ok := c.Writer.(http.Flusher)
+	if !ok {
+		t.Fatalf("expected gin writer to implement http.Flusher")
+	}
+
+	data := make(chan []byte)
+	errs := make(chan *interfaces.ErrorMessage, 1)
+	errs <- &interfaces.ErrorMessage{StatusCode: http.StatusInternalServerError, Error: errors.New("unexpected EOF")}
+	close(errs)
+
+	h.forwardResponsesStream(c, flusher, func(error) {}, data, errs)
+	body := recorder.Body.String()
+	if !strings.Contains(body, `"type":"error"`) {
+		t.Fatalf("expected responses error chunk, got: %q", body)
+	}
+	if strings.Contains(body, `"error":{`) {
+		t.Fatalf("expected streaming error chunk (top-level type), got HTTP error body: %q", body)
+	}
+}

sdk/api/handlers/openai_responses_stream_error.go

@@ -0,0 +1,119 @@
+package handlers
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+)
+
+type openAIResponsesStreamErrorChunk struct {
+	Type           string `json:"type"`
+	Code           string `json:"code"`
+	Message        string `json:"message"`
+	SequenceNumber int    `json:"sequence_number"`
+}
+
+func openAIResponsesStreamErrorCode(status int) string {
+	switch status {
+	case http.StatusUnauthorized:
+		return "invalid_api_key"
+	case http.StatusForbidden:
+		return "insufficient_quota"
+	case http.StatusTooManyRequests:
+		return "rate_limit_exceeded"
+	case http.StatusNotFound:
+		return "model_not_found"
+	case http.StatusRequestTimeout:
+		return "request_timeout"
+	default:
+		if status >= http.StatusInternalServerError {
+			return "internal_server_error"
+		}
+		if status >= http.StatusBadRequest {
+			return "invalid_request_error"
+		}
+		return "unknown_error"
+	}
+}
+
+// BuildOpenAIResponsesStreamErrorChunk builds an OpenAI Responses streaming error chunk.
+//
+// Important: OpenAI's HTTP error bodies are shaped like {"error":{...}}; those are valid for
+// non-streaming responses, but streaming clients validate SSE `data:` payloads against a union
+// of chunks that requires a top-level `type` field.
+func BuildOpenAIResponsesStreamErrorChunk(status int, errText string, sequenceNumber int) []byte {
+	if status <= 0 {
+		status = http.StatusInternalServerError
+	}
+	if sequenceNumber < 0 {
+		sequenceNumber = 0
+	}
+
+	message := strings.TrimSpace(errText)
+	if message == "" {
+		message = http.StatusText(status)
+	}
+
+	code := openAIResponsesStreamErrorCode(status)
+
+	trimmed := strings.TrimSpace(errText)
+	if trimmed != "" && json.Valid([]byte(trimmed)) {
+		var payload map[string]any
+		if err := json.Unmarshal([]byte(trimmed), &payload); err == nil {
+			if t, ok := payload["type"].(string); ok && strings.TrimSpace(t) == "error" {
+				if m, ok := payload["message"].(string); ok && strings.TrimSpace(m) != "" {
+					message = strings.TrimSpace(m)
+				}
+				if v, ok := payload["code"]; ok && v != nil {
+					if c, ok := v.(string); ok && strings.TrimSpace(c) != "" {
+						code = strings.TrimSpace(c)
+					} else {
+						code = strings.TrimSpace(fmt.Sprint(v))
+					}
+				}
+				if v, ok := payload["sequence_number"].(float64); ok && sequenceNumber == 0 {
+					sequenceNumber = int(v)
+				}
+			}
+			if e, ok := payload["error"].(map[string]any); ok {
+				if m, ok := e["message"].(string); ok && strings.TrimSpace(m) != "" {
+					message = strings.TrimSpace(m)
+				}
+				if v, ok := e["code"]; ok && v != nil {
+					if c, ok := v.(string); ok && strings.TrimSpace(c) != "" {
+						code = strings.TrimSpace(c)
+					} else {
+						code = strings.TrimSpace(fmt.Sprint(v))
+					}
+				}
+			}
+		}
+	}
+
+	if strings.TrimSpace(code) == "" {
+		code = "unknown_error"
+	}
+
+	data, err := json.Marshal(openAIResponsesStreamErrorChunk{
+		Type:           "error",
+		Code:           code,
+		Message:        message,
+		SequenceNumber: sequenceNumber,
+	})
+	if err == nil {
+		return data
+	}
+
+	// Extremely defensive fallback.
+	data, _ = json.Marshal(openAIResponsesStreamErrorChunk{
+		Type:           "error",
+		Code:           "internal_server_error",
+		Message:        message,
+		SequenceNumber: sequenceNumber,
+	})
+	if len(data) > 0 {
+		return data
+	}
+	return []byte(`{"type":"error","code":"internal_server_error","message":"internal error","sequence_number":0}`)
+}

sdk/api/handlers/openai_responses_stream_error_test.go

@@ -0,0 +1,48 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+)
+
+func TestBuildOpenAIResponsesStreamErrorChunk(t *testing.T) {
+	chunk := BuildOpenAIResponsesStreamErrorChunk(http.StatusInternalServerError, "unexpected EOF", 0)
+	var payload map[string]any
+	if err := json.Unmarshal(chunk, &payload); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if payload["type"] != "error" {
+		t.Fatalf("type = %v, want %q", payload["type"], "error")
+	}
+	if payload["code"] != "internal_server_error" {
+		t.Fatalf("code = %v, want %q", payload["code"], "internal_server_error")
+	}
+	if payload["message"] != "unexpected EOF" {
+		t.Fatalf("message = %v, want %q", payload["message"], "unexpected EOF")
+	}
+	if payload["sequence_number"] != float64(0) {
+		t.Fatalf("sequence_number = %v, want %v", payload["sequence_number"], 0)
+	}
+}
+
+func TestBuildOpenAIResponsesStreamErrorChunkExtractsHTTPErrorBody(t *testing.T) {
+	chunk := BuildOpenAIResponsesStreamErrorChunk(
+		http.StatusInternalServerError,
+		`{"error":{"message":"oops","type":"server_error","code":"internal_server_error"}}`,
+		0,
+	)
+	var payload map[string]any
+	if err := json.Unmarshal(chunk, &payload); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if payload["type"] != "error" {
+		t.Fatalf("type = %v, want %q", payload["type"], "error")
+	}
+	if payload["code"] != "internal_server_error" {
+		t.Fatalf("code = %v, want %q", payload["code"], "internal_server_error")
+	}
+	if payload["message"] != "oops" {
+		t.Fatalf("message = %v, want %q", payload["message"], "oops")
+	}
+}