tui: scroll content view with output

clean up msgResponseChunk handling

pkg/tui/tui.go

@@ -125,19 +125,16 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		m.updateContent()
 	case msgResponseChunk:
 		chunk := string(msg)
-		if len(m.messages) > 0 {
-			i := len(m.messages) - 1
-			switch m.messages[i].Role {
-			case models.MessageRoleAssistant:
-				m.messages[i].Content += chunk
-			default:
+		last := len(m.messages) - 1
+		if last >= 0 && m.messages[last].Role == models.MessageRoleAssistant {
+			m.messages[last].Content += chunk
+		} else {
 			m.messages = append(m.messages, models.Message{
 				Role:    models.MessageRoleAssistant,
 				Content: chunk,
 			})
 		}
 		m.updateContent()
-		}
 		cmd = waitForChunk(m.replyChan) // wait for the next chunk
 	case msgResponseEnd:
 		m.replyCancelFunc = nil
@@ -315,7 +312,12 @@ func (m *model) updateContent() {
 			sb.WriteString("\n\n")
 		}
 	}
+	atBottom := m.content.AtBottom()
 	m.content.SetContent(sb.String())
+	if atBottom {
+		// if we were at bottom before the update, scroll with the output
+		m.content.GotoBottom()
+	}
 }
 
 func (m model) inputView() string {