feat: Phase 2 — chat templates, reasoning parser, collapsible TUI, mouse support

- internal/llama/template.go: ChatML/Llama3 template engine with stop tokens
- internal/agent/reasoning.go: parse <think>/<reasoning> tags from LLM output
- companion/promptbuilder.go: output structured BuildResult, add date/time context
- agent/agent.go: wire templates + reasoning split into message loop
- storage: add reasoning TEXT column to messages table + migration
- channel/tui.go: collapsible reasoning (tab toggle), mouse scroll, polished dimmed style
- config: CHAT_TEMPLATE env var (chatml|llama3|none)
- plan.md: mark Phase 2 complete, add themes TODO

internal/channel/tui.go

@@ -23,6 +23,22 @@ var (
 			Foreground(lipgloss.Color("#10B981")).
 			Bold(true)
 
+	reasoningLabelStyle = lipgloss.NewStyle().
+				Foreground(lipgloss.Color("#6B7280")).
+				Background(lipgloss.Color("#1F2937")).
+				Padding(0, 1).
+				Italic(true)
+
+	reasoningContentStyle = lipgloss.NewStyle().
+				Foreground(lipgloss.Color("#6B7280")).
+				Italic(true)
+
+	reasoningHeaderStyle = lipgloss.NewStyle().
+				Foreground(lipgloss.Color("#6B7280")).
+				Background(lipgloss.Color("#1F2937")).
+				Padding(0, 1).
+				Bold(true)
+
 	inputStyle = lipgloss.NewStyle().
 			BorderStyle(lipgloss.NormalBorder()).
 			BorderForeground(lipgloss.Color("#374151"))
@@ -40,20 +56,23 @@ type model struct {
 	ctx    context.Context
 	cancel context.CancelFunc
 
-	viewport viewport.Model
-	input    string
-	state    sessionState
-	messages []types.Message
-	ready    bool
+	viewport          viewport.Model
+	input             string
+	state             sessionState
+	messages          []types.Message
+	reasoningExpanded map[string]bool
+	reasoningOrder    []string
+	ready             bool
 }
 
 func NewTUIModel(a *agent.Agent) tea.Model {
 	ctx, cancel := context.WithCancel(context.Background())
 	return &model{
-		agent:  a,
-		ctx:    ctx,
-		cancel: cancel,
-		state:  stateReady,
+		agent:             a,
+		ctx:               ctx,
+		cancel:            cancel,
+		state:             stateReady,
+		reasoningExpanded: make(map[string]bool),
 	}
 }
 
@@ -74,6 +93,11 @@ func (m *model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		}
 		return m, nil
 
+	case tea.MouseMsg:
+		var cmd tea.Cmd
+		m.viewport, cmd = m.viewport.Update(msg)
+		return m, cmd
+
 	case tea.KeyMsg:
 		switch msg.String() {
 		case "ctrl+c", "ctrl+q":
@@ -88,6 +112,15 @@ func (m *model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				return m, m.sendMessage(input)
 			}
 
+		case "tab":
+			for i := len(m.messages) - 1; i >= 0; i-- {
+				if m.messages[i].Role == types.RoleAssistant && m.messages[i].Reasoning != "" {
+					id := m.messages[i].ID
+					m.reasoningExpanded[id] = !m.reasoningExpanded[id]
+					break
+				}
+			}
+
 		case "backspace":
 			if len(m.input) > 0 {
 				m.input = m.input[:len(m.input)-1]
@@ -107,7 +140,22 @@ func (m *model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				Content: fmt.Sprintf("error: %v", msg.err),
 			})
 		} else {
-			m.messages = m.agent.Messages()
+			newMsgs := m.agent.Messages()
+			for _, msg := range newMsgs {
+				if msg.Role == types.RoleAssistant && msg.Reasoning != "" {
+					found := false
+					for _, id := range m.reasoningOrder {
+						if id == msg.ID {
+							found = true
+							break
+						}
+					}
+					if !found {
+						m.reasoningOrder = append(m.reasoningOrder, msg.ID)
+					}
+				}
+			}
+			m.messages = newMsgs
 		}
 		m.viewport.GotoBottom()
 	}
@@ -134,14 +182,26 @@ func (m *model) View() string {
 		default:
 			prefix = "system"
 		}
-		b.WriteString(style.Render(prefix+": ") + msg.Content + "\n\n")
+		b.WriteString(style.Render(prefix+": ") + msg.Content + "\n")
+
+		if msg.Role == types.RoleAssistant && msg.Reasoning != "" {
+			if m.reasoningExpanded[msg.ID] {
+				b.WriteString(reasoningHeaderStyle.Render(" reasoning ") + "\n")
+				b.WriteString(reasoningContentStyle.Render(msg.Reasoning) + "\n")
+			} else {
+				label := reasoningLabelStyle.Render(" ` reasoning (tab)")
+				b.WriteString(label + "\n")
+			}
+		}
+
+		b.WriteString("\n")
 	}
 
 	m.viewport.SetContent(b.String())
 
 	prompt := "> "
 	if m.state == stateWaiting {
-		prompt = "waiting... "
+		prompt = "... "
 	}
 
 	return fmt.Sprintf("%s\n%s%s", m.viewport.View(), inputStyle.Render(prompt), m.input)