diff --git a/agent/assistant/agent.go b/agent/assistant/agent.go
index dcdb15b5..6803da38 100644
--- a/agent/assistant/agent.go
+++ b/agent/assistant/agent.go
@@ -176,6 +176,7 @@ func (ast *Assistant) Stream(ctx *context.Context, inputMessages []context.Messa
 			ctx.Logger.Debug("Create hook delegating to agent: %s", createResponse.Delegate.AgentID)
 
 			// Delegate to target agent (reuse existing delegation logic from next.go)
+			// Note: User input is already buffered by root agent, delegated agent will skip buffering
 			delegateResponse, err := ast.handleDelegation(ctx, createResponse.Delegate, streamHandler)
 			if err != nil {
 				finalStatus = context.ResumeStatusFailed
diff --git a/agent/assistant/chat.go b/agent/assistant/chat.go
index 381472fe..f714950c 100644
--- a/agent/assistant/chat.go
+++ b/agent/assistant/chat.go
@@ -237,6 +237,12 @@ func (ast *Assistant) BufferUserInput(ctx *agentcontext.Context, inputMessages [
 		return
 	}
 
+	// Only root stack should buffer user input
+	// Delegated agents share the same buffer but should not duplicate user input
+	if ctx.Stack != nil && !ctx.Stack.IsRoot() {
+		return
+	}
+
 	// Convert input messages to buffer format
 	for _, msg := range inputMessages {
 		// Extract content from message
diff --git a/agent/assistant/next.go b/agent/assistant/next.go
index accacaab..779b36c2 100644
--- a/agent/assistant/next.go
+++ b/agent/assistant/next.go
@@ -15,6 +15,7 @@ func (ast *Assistant) processNextResponse(npc *NextProcessContext) (*agentContex
 	}
 
 	// Handle Delegate: call another agent
+	// Note: User input is already buffered by root agent, delegated agent will skip buffering
 	if npc.NextResponse.Delegate != nil {
 		return ast.handleDelegation(npc.Context, npc.NextResponse.Delegate, npc.StreamHandler)
 	}