[CAP-9371] show loading spinner in content pane only, keeping header and footer visible (#315)

Previously, the loading spinner took over the entire screen (including header and footer), which created a jarring effect when navigating between models. Now, the loading spinner only uses the content pane, allowing the header and footer to remain in place during loading. This also allows the breadcrumbs (the header) to update and display immediately so users know what they're waiting for.

GitOrigin-RevId: 23ce64fe1dabff6b612a6e0118333927613029bc

Author: blue-keleher

pkg/tui/stack.go

@@ -244,19 +244,33 @@ func (m *StackModel) StackSizeMsg() StackSizeMsg {
 }
 
 func (m *StackModel) View() string {
+	if len(m.stack) == 0 {
+		if m.loadingSpinner != nil {
+			loadingTmpl := "%s Loading..."
+			if m.loadingMsg != "" {
+				loadingTmpl = m.loadingMsg
+			}
+			return lipgloss.Place(m.width, m.height, lipgloss.Center, lipgloss.Center, fmt.Sprintf(loadingTmpl, m.loadingSpinner.View()))
+		}
+		return ""
+	}
+
+	header := m.header()
+	footer := m.footer()
+
+	var content string
 	if m.loadingSpinner != nil {
 		loadingTmpl := "%s Loading..."
 		if m.loadingMsg != "" {
 			loadingTmpl = m.loadingMsg
 		}
-		return lipgloss.Place(m.width, m.height, lipgloss.Center, lipgloss.Center, fmt.Sprintf(loadingTmpl, m.loadingSpinner.View()))
-	}
-
-	if len(m.stack) == 0 {
-		return ""
+		contentHeight := m.height - lipgloss.Height(header) - lipgloss.Height(footer)
+		content = lipgloss.Place(m.width, contentHeight, lipgloss.Center, lipgloss.Center, fmt.Sprintf(loadingTmpl, m.loadingSpinner.View()))
+	} else {
+		content = m.stack[len(m.stack)-1].Model.View()
 	}
 
-	return lipgloss.JoinVertical(lipgloss.Left, m.header(), m.stack[len(m.stack)-1].Model.View(), m.footer())
+	return lipgloss.JoinVertical(lipgloss.Left, header, content, footer)
 }
 
 func (m *StackModel) header() string {
@@ -293,7 +307,7 @@ func (m *StackModel) footer() string {
 		commands = append(commands, prevCommand)
 	}
 
-	if m.stack[len(m.stack)-1].Cmd != "" {
+	if len(m.stack) > 0 && m.stack[len(m.stack)-1].Cmd != "" {
 		commands = append(commands, saveToClipboard)
 	}