agent: simplify loop — Run as function, fix stop condition

- Loop struct and New constructor removed; Run is now a package-level
  function taking (ctx, Config, State)
- Stop condition de-nested: natural stop (no tool calls → MarkComplete
  + break) and step-limit stop (step >= maxSteps-1 → break) are now
  separate, sequential checks instead of a redundant outer/inner pair

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agent/loop.go

@@ -29,28 +29,20 @@ type Config struct {
 	SystemPrompt string
 }
 
-type Loop struct {
-	cfg Config
-}
-
-func New(cfg Config) *Loop {
-	return &Loop{cfg: cfg}
-}
-
-func (l *Loop) Run(ctx context.Context, state State) error {
-	maxSteps := l.cfg.MaxSteps
+func Run(ctx context.Context, cfg Config, state State) error {
+	maxSteps := cfg.MaxSteps
 	if maxSteps <= 0 {
 		maxSteps = 1
 	}
 
 	for step := range maxSteps {
 		history := state.History()
-		if l.cfg.SystemPrompt != "" {
-			history = append([]backend.Message{{Role: "system", Content: l.cfg.SystemPrompt}}, history...)
+		if cfg.SystemPrompt != "" {
+			history = append([]backend.Message{{Role: "system", Content: cfg.SystemPrompt}}, history...)
 		}
 
 		// Stream the assistant's response.
-		ch, err := l.cfg.Backend.ChatStream(ctx, l.cfg.Model, history, l.cfg.Tools)
+		ch, err := cfg.Backend.ChatStream(ctx, cfg.Model, history, cfg.Tools)
 		if err != nil {
 			return fmt.Errorf("step %d: %w", step, err)
 		}
@@ -63,7 +55,7 @@ func (l *Loop) Run(ctx context.Context, state State) error {
 		for ev := range ch {
 			if ev.Content != "" {
 				content.WriteString(ev.Content)
-				l.emit(OutputMsg{Role: "assistant", Content: ev.Content})
+				emit(cfg, OutputMsg{Role: "assistant", Content: ev.Content})
 			}
 			toolCalls = append(toolCalls, ev.ToolCalls...)
 			if ev.Done {
@@ -82,12 +74,12 @@ func (l *Loop) Run(ctx context.Context, state State) error {
 		var results []ToolResult
 
 		for _, tc := range toolCalls {
-			l.emit(OutputMsg{Role: "call", Name: tc.Name, Content: string(tc.Arguments)})
+			emit(cfg, OutputMsg{Role: "call", Name: tc.Name, Content: string(tc.Arguments)})
 
 			var result string
 			var isErr bool
-			if l.cfg.Exec != nil {
-				out, err := l.cfg.Exec(tc.Name, tc.Arguments)
+			if cfg.Exec != nil {
+				out, err := cfg.Exec(tc.Name, tc.Arguments)
 				if err != nil {
 					result = fmt.Sprintf("error: %v", err)
 					isErr = true
@@ -105,34 +97,34 @@ func (l *Loop) Run(ctx context.Context, state State) error {
 				Content:    result,
 				IsError:    isErr,
 			})
-			l.emit(OutputMsg{Role: "tool", Name: tc.Name, Content: result})
+			emit(cfg, OutputMsg{Role: "tool", Name: tc.Name, Content: result})
 		}
 
 		// Emit usage when we have real token counts.
 		if usage.InputTokens > 0 || usage.OutputTokens > 0 {
-			l.emit(OutputMsg{Role: "usage", Usage: usage})
+			emit(cfg, OutputMsg{Role: "usage", Usage: usage})
 		}
 
 		if err := state.Update(msg, results); err != nil {
 			return fmt.Errorf("step %d update: %w", step, err)
 		}
 
-		// Stop when the model has nothing more to call.
-		if len(toolCalls) == 0 || step >= maxSteps-1 {
-			if len(toolCalls) == 0 {
-				if err := state.MarkComplete(); err != nil {
-					return fmt.Errorf("mark complete: %w", err)
-				}
+		if len(toolCalls) == 0 {
+			if err := state.MarkComplete(); err != nil {
+				return fmt.Errorf("mark complete: %w", err)
 			}
 			break
 		}
+		if step >= maxSteps-1 {
+			break
+		}
 	}
 
 	return nil
 }
 
-func (l *Loop) emit(msg OutputMsg) {
-	if l.cfg.Output != nil {
-		l.cfg.Output(msg)
+func emit(cfg Config, msg OutputMsg) {
+	if cfg.Output != nil {
+		cfg.Output(msg)
 	}
 }

main.go

@@ -570,7 +570,7 @@ func (m model) startAgent(session *agent.Session) (chan tea.Msg, context.CancelF
 			}
 		}
 
-		if err := agent.New(loopcfg).Run(ctx, session); err != nil {
+		if err := agent.Run(ctx, loopcfg, session); err != nil {
 			select {
 			case ch <- agentMsg{role: "error", content: err.Error()}:
 			case <-ctx.Done():