diff --git a/internal/executor/acp_executor.go b/internal/executor/acp_executor.go
index fd50f18..1c7666e 100644
--- a/internal/executor/acp_executor.go
+++ b/internal/executor/acp_executor.go
@@ -102,39 +102,8 @@ func (e *ACPExecutor) Execute(ctx context.Context, step *core.Step, execCtx *cor
 		Exports:   make(map[string]interface{}),
 	}
 
-	// Resolve agent name for the standalone function
-	agentName := step.Agent
-	var customCommand string
-	var customArgs []string
-	if agentName == "" && step.ACPConfig != nil && step.ACPConfig.Command != "" {
-		customCommand = step.ACPConfig.Command
-		customArgs = step.ACPConfig.Args
-	}
-
-	// For custom commands, use ResolveAgent + the old path
-	// For built-in agents, delegate to RunAgentACP
-	if customCommand != "" {
-		// Custom agent — validate command exists
-		_, err := exec.LookPath(customCommand)
-		if err != nil {
-			err = fmt.Errorf("agent command %q not found in PATH: %w", customCommand, err)
-			result.Status = core.StepStatusFailed
-			result.Error = err
-			result.EndTime = time.Now()
-			result.Duration = result.EndTime.Sub(result.StartTime)
-			return result, err
-		}
-		// Custom agents not supported by RunAgentACP — keep original error
-		_ = customArgs
-		err = fmt.Errorf("custom agent commands should use 'agent' field with a built-in agent name; use acp_config for custom agents via workflow steps only")
-		result.Status = core.StepStatusFailed
-		result.Error = err
-		result.EndTime = time.Now()
-		result.Duration = result.EndTime.Sub(result.StartTime)
-		return result, err
-	}
-
 	// Validate we have an agent
+	agentName := step.Agent
 	if agentName == "" {
 		err := fmt.Errorf("agent-acp step requires 'agent' field or 'acp_config.command'")
 		result.Status = core.StepStatusFailed
@@ -298,6 +267,7 @@ func RunAgentACP(ctx context.Context, prompt, agentName string, cfg *RunAgentACP
 	}()
 
 	defer func() {
+		_ = stdinPipe.Close()
 		_ = stderrWriter.Close()
 		stderrWg.Wait()
 		if cmd.Process != nil {
@@ -426,11 +396,13 @@ func resolveAgentName(step *core.Step) string {
 	return "unknown"
 }
 
+// IsBuiltinAgent returns true if the given name is a built-in ACP agent.
+func IsBuiltinAgent(name string) bool {
+	_, ok := builtinACPAgents[name]
+	return ok
+}
+
 // availableAgentNames returns a comma-separated list of built-in agent names.
 func availableAgentNames() string {
-	names := make([]string, 0, len(builtinACPAgents))
-	for name := range builtinACPAgents {
-		names = append(names, name)
-	}
-	return strings.Join(names, ", ")
+	return strings.Join(ListAgentNames(), ", ")
 }
diff --git a/pkg/cli/agent.go b/pkg/cli/agent.go
index 7be8c7b..3304aa8 100644
--- a/pkg/cli/agent.go
+++ b/pkg/cli/agent.go
@@ -75,17 +75,12 @@ func runAgent(cmd *cobra.Command, args []string) error {
 		StreamWriter: os.Stdout,
 	}
 
-	output, _, err := executor.RunAgentACP(ctx, message, agentName, cfg)
+	_, _, err = executor.RunAgentACP(ctx, message, agentName, cfg)
 	if err != nil {
 		printer.Error("Agent failed: %s", err)
 		return err
 	}
 
-	// If there was no stream writer, print output at the end
-	if cfg.StreamWriter == nil && output != "" {
-		fmt.Println(output)
-	}
-
 	return nil
 }
 
diff --git a/pkg/server/handlers/agent_chat.go b/pkg/server/handlers/agent_chat.go
index 98509f5..150aa36 100644
--- a/pkg/server/handlers/agent_chat.go
+++ b/pkg/server/handlers/agent_chat.go
@@ -165,10 +165,8 @@ func resolveAgentName(model string) string {
 	if model == "" {
 		return "claude-code"
 	}
-	for _, name := range executor.ListAgentNames() {
-		if name == model {
-			return model
-		}
+	if executor.IsBuiltinAgent(model) {
+		return model
 	}
 	return "claude-code"
 }