diff --git a/internal/ai/runtime/internal/impl/callbacks/runlog_callback.go b/internal/ai/runtime/internal/impl/callbacks/runlog_callback.go
index 9aeb47e..ee01ac3 100644
--- a/internal/ai/runtime/internal/impl/callbacks/runlog_callback.go
+++ b/internal/ai/runtime/internal/impl/callbacks/runlog_callback.go
@@ -18,9 +18,6 @@ func NewRuntimeTraceCollector() *RuntimeTraceCollector {
 }
 
 func (c *RuntimeTraceCollector) Marshal() string {
-	if c == nil {
-		return ""
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	buf, err := json.Marshal(c.Data)
@@ -31,9 +28,6 @@ func (c *RuntimeTraceCollector) Marshal() string {
 }
 
 func (c *RuntimeTraceCollector) SetTooling(staticToolCodes []string, dynamicToolCodes []string, toolSearchEnabled bool) {
-	if c == nil {
-		return
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.Data.Input.StaticToolCodes = append([]string(nil), staticToolCodes...)
@@ -42,9 +36,6 @@ func (c *RuntimeTraceCollector) SetTooling(staticToolCodes []string, dynamicTool
 }
 
 func (c *RuntimeTraceCollector) SetInstructionSummary(summary InstructionTraceSummary) {
-	if c == nil {
-		return
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.Data.Instruction.SectionTitles = append([]string(nil), summary.SectionTitles...)
@@ -54,9 +45,6 @@ func (c *RuntimeTraceCollector) SetInstructionSummary(summary InstructionTraceSu
 }
 
 func (c *RuntimeTraceCollector) SetSkillMiddleware(enabled bool, toolName string) {
-	if c == nil {
-		return
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.Data.Skill.MiddlewareEnabled = enabled
@@ -71,7 +59,7 @@ type SkillMetadata struct {
 }
 
 func (c *RuntimeTraceCollector) SetVisibleSkills(skills map[string]SkillMetadata) {
-	if c == nil || len(skills) == 0 {
+	if len(skills) == 0 {
 		return
 	}
 	c.mu.Lock()
@@ -87,9 +75,6 @@ func (c *RuntimeTraceCollector) SetVisibleSkills(skills map[string]SkillMetadata
 }
 
 func (c *RuntimeTraceCollector) ActivateSkill(skill SkillMetadata, routeReason string, routeTrace string) {
-	if c == nil {
-		return
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.Data.Skill.Code = skill.Code
@@ -101,18 +86,12 @@ func (c *RuntimeTraceCollector) ActivateSkill(skill SkillMetadata, routeReason s
 }
 
 func (c *RuntimeTraceCollector) SetFilteredToolCodes(toolCodes []string) {
-	if c == nil {
-		return
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.Data.Skill.FilteredToolCodes = append([]string(nil), toolCodes...)
 }
 
 func (c *RuntimeTraceCollector) SetRetrieverSummary(summary RetrieverTraceSummary) {
-	if c == nil {
-		return
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.Data.Retriever.TopK = summary.TopK
@@ -128,9 +107,6 @@ func (c *RuntimeTraceCollector) SetRetrieverSummary(summary RetrieverTraceSummar
 }
 
 func (c *RuntimeTraceCollector) AddToolItem(item ToolTraceItem) {
-	if c == nil {
-		return
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.Data.Tools.Count++
@@ -138,9 +114,6 @@ func (c *RuntimeTraceCollector) AddToolItem(item ToolTraceItem) {
 }
 
 func (c *RuntimeTraceCollector) AddToolSearchItem(item ToolSearchTraceItem) {
-	if c == nil {
-		return
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.Data.ToolSearch.Count++
@@ -148,9 +121,6 @@ func (c *RuntimeTraceCollector) AddToolSearchItem(item ToolSearchTraceItem) {
 }
 
 func (c *RuntimeTraceCollector) AddGraphToolItem(item GraphToolTraceItem) {
-	if c == nil {
-		return
-	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.Data.GraphTools.Count++
diff --git a/internal/ai/runtime/internal/impl/factory/agent_factory.go b/internal/ai/runtime/internal/impl/factory/agent_factory.go
index dc89c38..132b428 100644
--- a/internal/ai/runtime/internal/impl/factory/agent_factory.go
+++ b/internal/ai/runtime/internal/impl/factory/agent_factory.go
@@ -55,7 +55,7 @@ func NewAgentFactory() *AgentFactory {
 		chatModelFactory:   NewChatModelFactory(),
 		toolFactory:        NewToolFactory(),
 		instructionService: instruction.NewService(nil, nil, nil),
-		handlerService:     NewAgentHandlerService(nil),
+		handlerService:     NewAgentHandlerService(NewSkillMiddlewareService()),
 	}
 }
 
@@ -73,21 +73,19 @@ func (f *AgentFactory) BuildCustomerServiceAgent(ctx context.Context, input Buil
 	allTools = append(allTools, input.StaticTools...)
 	instructionResult := f.instructionService.Build(input.AIAgent, nil, input.InstructionToolDefinitions, input.StaticToolCodes)
 	handlers := make([]adk.ChatModelAgentMiddleware, 0, 3)
-	if f.handlerService != nil {
-		builtHandlers, err := f.handlerService.Build(ctx, BuildAgentHandlersInput{
-			AIAgent:                    input.AIAgent,
-			InstructionToolDefinitions: input.InstructionToolDefinitions,
-			DynamicToolDefinitions:     input.DynamicMCPToolDefinitions,
-			DynamicTools:               dynamicTools,
-			StaticToolMetadata:         input.StaticToolMetadata,
-			Collector:                  input.Collector,
-			InstructionSummary:         buildInstructionTraceSummary(instructionResult.Summary),
-		})
-		if err != nil {
-			return nil, err
-		}
-		handlers = append(handlers, builtHandlers...)
+	builtHandlers, err := f.handlerService.Build(ctx, BuildAgentHandlersInput{
+		AIAgent:                    input.AIAgent,
+		InstructionToolDefinitions: input.InstructionToolDefinitions,
+		DynamicToolDefinitions:     input.DynamicMCPToolDefinitions,
+		DynamicTools:               dynamicTools,
+		StaticToolMetadata:         input.StaticToolMetadata,
+		Collector:                  input.Collector,
+		InstructionSummary:         buildInstructionTraceSummary(instructionResult.Summary),
+	})
+	if err != nil {
+		return nil, err
 	}
+	handlers = append(handlers, builtHandlers...)
 	inner, err := adk.NewChatModelAgent(ctx, &adk.ChatModelAgentConfig{
 		Name:        strings.TrimSpace(input.AIAgent.Name),
 		Description: strings.TrimSpace(input.AIAgent.Description),
diff --git a/internal/ai/runtime/internal/impl/factory/agent_handler_service.go b/internal/ai/runtime/internal/impl/factory/agent_handler_service.go
index 5783b33..8138342 100644
--- a/internal/ai/runtime/internal/impl/factory/agent_handler_service.go
+++ b/internal/ai/runtime/internal/impl/factory/agent_handler_service.go
@@ -31,7 +31,7 @@ type BuildAgentHandlersInput struct {
 
 func NewAgentHandlerService(skillMiddleware *SkillMiddlewareService) *AgentHandlerService {
 	if skillMiddleware == nil {
-		skillMiddleware = NewSkillMiddlewareService()
+		panic("skill middleware is required")
 	}
 	return &AgentHandlerService{skillMiddleware: skillMiddleware}
 }
diff --git a/internal/ai/runtime/internal/impl/factory/agent_handler_service_test.go b/internal/ai/runtime/internal/impl/factory/agent_handler_service_test.go
index e607634..ea4e9d9 100644
--- a/internal/ai/runtime/internal/impl/factory/agent_handler_service_test.go
+++ b/internal/ai/runtime/internal/impl/factory/agent_handler_service_test.go
@@ -9,7 +9,7 @@ import (
 
 func TestAgentHandlerServiceBuildWithCollectorOnly(t *testing.T) {
 	collector := einocallbacks.NewRuntimeTraceCollector()
-	service := NewAgentHandlerService(nil)
+	service := NewAgentHandlerService(NewSkillMiddlewareService())
 
 	handlers, err := service.Build(context.Background(), BuildAgentHandlersInput{
 		Collector: collector,
@@ -33,7 +33,7 @@ func TestAgentHandlerServiceBuildWithCollectorOnly(t *testing.T) {
 }
 
 func TestAgentHandlerServiceBuildWithEmptyInput(t *testing.T) {
-	service := NewAgentHandlerService(nil)
+	service := NewAgentHandlerService(NewSkillMiddlewareService())
 
 	handlers, err := service.Build(context.Background(), BuildAgentHandlersInput{})
 	if err != nil {
diff --git a/internal/ai/runtime/reply_interrupt_service.go b/internal/ai/runtime/reply_interrupt_service.go
index 99073be..51618b4 100644
--- a/internal/ai/runtime/reply_interrupt_service.go
+++ b/internal/ai/runtime/reply_interrupt_service.go
@@ -2,6 +2,7 @@ package runtime
 
 import (
 	"context"
+	"fmt"
 	"strings"
 
 	applicationruntime "cs-agent/internal/ai/application/runtime"
@@ -16,8 +17,8 @@ func newReplyInterruptService() *replyInterruptService {
 }
 
 func (s *replyInterruptService) ResumePendingInterrupt(ctx context.Context, owner *aiReplyService, replyCtx aiReplyContext) error {
-	if replyCtx.PendingInterrupt == nil || owner == nil {
-		return nil
+	if replyCtx.PendingInterrupt == nil {
+		return fmt.Errorf("pending interrupt is required")
 	}
 	summary, err := owner.executor.ResumePendingInterrupt(ctx, runtimeReplyResumeInput{
 		Conversation:     replyCtx.Conversation,
@@ -83,9 +84,6 @@ func (s *replyInterruptService) ResumePendingInterrupt(ctx context.Context, owne
 }
 
 func (s *replyInterruptService) HandleInterruptedSummary(owner *aiReplyService, replyCtx aiReplyContext, summary *applicationruntime.Summary) error {
-	if owner == nil {
-		return nil
-	}
 	pending := buildConversationInterrupt(replyCtx.Conversation, replyCtx.Message, replyCtx.AIAgent, summary)
 	if err := svc.ConversationInterruptService.CreateOrUpdatePending(pending); err != nil {
 		return err
@@ -110,8 +108,8 @@ func (s *replyInterruptService) HandleInterruptedSummary(owner *aiReplyService,
 }
 
 func (s *replyInterruptService) HandleInterruptedResume(owner *aiReplyService, replyCtx aiReplyContext, summary *applicationruntime.Summary) error {
-	if replyCtx.PendingInterrupt == nil || owner == nil {
-		return nil
+	if replyCtx.PendingInterrupt == nil {
+		return fmt.Errorf("pending interrupt is required")
 	}
 	replyText := resolveInterruptPrompt(summary)
 	replyMessage, err := owner.commit.CommitAIReply(replyCommitInput{
diff --git a/internal/ai/runtime/runtime_reply_executor.go b/internal/ai/runtime/runtime_reply_executor.go
index 9143812..e876324 100644
--- a/internal/ai/runtime/runtime_reply_executor.go
+++ b/internal/ai/runtime/runtime_reply_executor.go
@@ -55,7 +55,7 @@ func (e *runtimeReplyExecutor) Run(ctx context.Context, input runtimeReplyRunInp
 
 func (e *runtimeReplyExecutor) ResumePendingInterrupt(ctx context.Context, input runtimeReplyResumeInput) (*applicationruntime.Summary, error) {
 	if input.PendingInterrupt == nil {
-		return nil, nil
+		return nil, fmt.Errorf("pending interrupt is required")
 	}
 	aiConfig := svc.AIConfigService.Get(input.AIAgent.AIConfigID)
 	if aiConfig == nil {