diff --git a/backend/internal/handler/gateway_handler.go b/backend/internal/handler/gateway_handler.go
index 7eb7007e..bbc9c181 100644
--- a/backend/internal/handler/gateway_handler.go
+++ b/backend/internal/handler/gateway_handler.go
@@ -586,8 +586,20 @@ func (h *GatewayHandler) handleStreamingAwareError(c *gin.Context, status int, e
 		// Stream already started, send error as SSE event then close
 		flusher, ok := c.Writer.(http.Flusher)
 		if ok {
-			// Send error event in SSE format
-			errorEvent := fmt.Sprintf(`data: {"type": "error", "error": {"type": "%s", "message": "%s"}}`+"\n\n", errType, message)
+			// Send error event in SSE format with proper JSON marshaling
+			errorData := map[string]any{
+				"type": "error",
+				"error": map[string]string{
+					"type":    errType,
+					"message": message,
+				},
+			}
+			jsonBytes, err := json.Marshal(errorData)
+			if err != nil {
+				_ = c.Error(err)
+				return
+			}
+			errorEvent := fmt.Sprintf("data: %s\n\n", string(jsonBytes))
 			if _, err := fmt.Fprint(c.Writer, errorEvent); err != nil {
 				_ = c.Error(err)
 			}
@@ -737,8 +749,27 @@ func sendMockWarmupStream(c *gin.Context, model string) {
 	c.Header("Connection", "keep-alive")
 	c.Header("X-Accel-Buffering", "no")
 
+	// Build message_start event with proper JSON marshaling
+	messageStart := map[string]any{
+		"type": "message_start",
+		"message": map[string]any{
+			"id":            "msg_mock_warmup",
+			"type":          "message",
+			"role":          "assistant",
+			"model":         model,
+			"content":       []any{},
+			"stop_reason":   nil,
+			"stop_sequence": nil,
+			"usage": map[string]int{
+				"input_tokens":  10,
+				"output_tokens": 0,
+			},
+		},
+	}
+	messageStartJSON, _ := json.Marshal(messageStart)
+
 	events := []string{
-		`event: message_start` + "\n" + `data: {"message":{"content":[],"id":"msg_mock_warmup","model":"` + model + `","role":"assistant","stop_reason":null,"stop_sequence":null,"type":"message","usage":{"input_tokens":10,"output_tokens":0}},"type":"message_start"}`,
+		`event: message_start` + "\n" + `data: ` + string(messageStartJSON),
 		`event: content_block_start` + "\n" + `data: {"content_block":{"text":"","type":"text"},"index":0,"type":"content_block_start"}`,
 		`event: content_block_delta` + "\n" + `data: {"delta":{"text":"New","type":"text_delta"},"index":0,"type":"content_block_delta"}`,
 		`event: content_block_delta` + "\n" + `data: {"delta":{"text":" Conversation","type":"text_delta"},"index":0,"type":"content_block_delta"}`,
diff --git a/backend/internal/handler/gateway_helper.go b/backend/internal/handler/gateway_helper.go
index 4e049dbb..9d2e4a9d 100644
--- a/backend/internal/handler/gateway_helper.go
+++ b/backend/internal/handler/gateway_helper.go
@@ -144,6 +144,21 @@ func (h *ConcurrencyHelper) waitForSlotWithPingTimeout(c *gin.Context, slotType
 	ctx, cancel := context.WithTimeout(c.Request.Context(), timeout)
 	defer cancel()
 
+	// Try immediate acquire first (avoid unnecessary wait)
+	var result *service.AcquireResult
+	var err error
+	if slotType == "user" {
+		result, err = h.concurrencyService.AcquireUserSlot(ctx, id, maxConcurrency)
+	} else {
+		result, err = h.concurrencyService.AcquireAccountSlot(ctx, id, maxConcurrency)
+	}
+	if err != nil {
+		return nil, err
+	}
+	if result.Acquired {
+		return result.ReleaseFunc, nil
+	}
+
 	// Determine if ping is needed (streaming + ping format defined)
 	needPing := isStream && h.pingFormat != ""
 
diff --git a/backend/internal/pkg/antigravity/request_transformer_test.go b/backend/internal/pkg/antigravity/request_transformer_test.go
index ba07893f..56eebad0 100644
--- a/backend/internal/pkg/antigravity/request_transformer_test.go
+++ b/backend/internal/pkg/antigravity/request_transformer_test.go
@@ -96,7 +96,7 @@ func TestBuildTools_CustomTypeTools(t *testing.T) {
 				{
 					Type: "custom",
 					Name: "mcp_tool",
-					Custom: &CustomToolSpec{
+					Custom: &ClaudeCustomToolSpec{
 						Description: "MCP tool description",
 						InputSchema: map[string]any{
 							"type": "object",
@@ -121,7 +121,7 @@ func TestBuildTools_CustomTypeTools(t *testing.T) {
 				{
 					Type: "custom",
 					Name: "custom_tool",
-					Custom: &CustomToolSpec{
+					Custom: &ClaudeCustomToolSpec{
 						Description: "Custom tool",
 						InputSchema: map[string]any{"type": "object"},
 					},
@@ -148,7 +148,7 @@ func TestBuildTools_CustomTypeTools(t *testing.T) {
 				{
 					Type: "custom",
 					Name: "invalid_custom",
-					Custom: &CustomToolSpec{
+					Custom: &ClaudeCustomToolSpec{
 						Description: "Invalid",
 						// InputSchema 为 nil
 					},
diff --git a/backend/internal/repository/concurrency_cache.go b/backend/internal/repository/concurrency_cache.go
index 35296497..95370f51 100644
--- a/backend/internal/repository/concurrency_cache.go
+++ b/backend/internal/repository/concurrency_cache.go
@@ -151,11 +151,17 @@ var (
 			return 1
 		`)
 
-	// getAccountsLoadBatchScript - batch load query (read-only)
-	// ARGV[1] = slot TTL (seconds, retained for compatibility)
+	// getAccountsLoadBatchScript - batch load query with expired slot cleanup
+	// ARGV[1] = slot TTL (seconds)
 	// ARGV[2..n] = accountID1, maxConcurrency1, accountID2, maxConcurrency2, ...
 	getAccountsLoadBatchScript = redis.NewScript(`
 			local result = {}
+			local slotTTL = tonumber(ARGV[1])
+
+			-- Get current server time
+			local timeResult = redis.call('TIME')
+			local nowSeconds = tonumber(timeResult[1])
+			local cutoffTime = nowSeconds - slotTTL
 
 			local i = 2
 			while i <= #ARGV do
@@ -163,6 +169,9 @@ var (
 				local maxConcurrency = tonumber(ARGV[i + 1])
 
 				local slotKey = 'concurrency:account:' .. accountID
+
+				-- Clean up expired slots before counting
+				redis.call('ZREMRANGEBYSCORE', slotKey, '-inf', cutoffTime)
 				local currentConcurrency = redis.call('ZCARD', slotKey)
 
 				local waitKey = 'wait:account:' .. accountID
diff --git a/backend/internal/service/gateway_service.go b/backend/internal/service/gateway_service.go
index 3932c35c..bd6f59f7 100644
--- a/backend/internal/service/gateway_service.go
+++ b/backend/internal/service/gateway_service.go
@@ -204,7 +204,7 @@ func (s *GatewayService) GenerateSessionHash(parsed *ParsedRequest) string {
 
 // BindStickySession sets session -> account binding with standard TTL.
 func (s *GatewayService) BindStickySession(ctx context.Context, sessionHash string, accountID int64) error {
-	if sessionHash == "" || accountID <= 0 {
+	if sessionHash == "" || accountID <= 0 || s.cache == nil {
 		return nil
 	}
 	return s.cache.SetSessionAccountID(ctx, sessionHash, accountID, stickySessionTTL)
@@ -429,7 +429,7 @@ func (s *GatewayService) SelectAccountWithLoadAwareness(ctx context.Context, gro
 	}
 
 	// ============ Layer 1: 粘性会话优先 ============
-	if sessionHash != "" {
+	if sessionHash != "" && s.cache != nil {
 		accountID, err := s.cache.GetSessionAccountID(ctx, sessionHash)
 		if err == nil && accountID > 0 && !isExcluded(accountID) {
 			account, err := s.accountRepo.GetByID(ctx, accountID)