diff --git a/README.md b/README.md
index c1a4254..7c18174 100644
--- a/README.md
+++ b/README.md
@@ -89,7 +89,7 @@ Pug automatically loads variables from a .tfvars file. It looks for a file named
 
 ### Explorer
 
-The explorer pane a tree of [modules](#module) and [workspaces](#workspace) discovered on your filesystem. From here, terraform commands can be carried out on both modules and workspaces.
+The explorer pane shows a tree of [modules](#module) and [workspaces](#workspace) discovered on your filesystem. From here, terraform commands can be carried out on both modules and workspaces.
 
 You can select multiple modules or workspaces; you cannot select a combination of the two. Any terraform commands are then carried out on the selection.
 
diff --git a/internal/pubsub/broker.go b/internal/pubsub/broker.go
index 470d4d4..5c07f9d 100644
--- a/internal/pubsub/broker.go
+++ b/internal/pubsub/broker.go
@@ -7,7 +7,7 @@ import (
 	"github.com/leg100/pug/internal/resource"
 )
 
-const bufferSize = 1024
+const bufferSize = 1024 * 1024
 
 type Logger interface {
 	Debug(msg string, args ...any)
diff --git a/internal/tui/border.go b/internal/tui/border.go
index e078e68..56ccb6a 100644
--- a/internal/tui/border.go
+++ b/internal/tui/border.go
@@ -90,8 +90,8 @@ func borderize(content string, active bool, embeddedText map[BorderPosition]stri
 		// Add the corners
 		return style.Render(leftCorner) + s + style.Render(rightCorner)
 	}
-	// Stack top border onto remaining borders
-	return lipgloss.JoinVertical(lipgloss.Top,
+	// Stack top border, content and horizontal borders, and bottom border.
+	return strings.Join([]string{
 		buildHorizontalBorder(
 			embeddedText[TopLeftBorder],
 			embeddedText[TopMiddleBorder],
@@ -111,5 +111,5 @@ func borderize(content string, active bool, embeddedText map[BorderPosition]stri
 			border.Bottom,
 			border.BottomRight,
 		),
-	)
+	}, "\n")
 }
diff --git a/internal/tui/explorer/messages.go b/internal/tui/explorer/messages.go
index e56227f..8a4ecad 100644
--- a/internal/tui/explorer/messages.go
+++ b/internal/tui/explorer/messages.go
@@ -1,3 +1,6 @@
 package explorer
 
-type builtTreeMsg *tree
+type builtTreeMsg struct {
+	tree     *tree
+	rendered string
+}
diff --git a/internal/tui/explorer/model.go b/internal/tui/explorer/model.go
index b450ed5..369e06d 100644
--- a/internal/tui/explorer/model.go
+++ b/internal/tui/explorer/model.go
@@ -10,7 +10,6 @@ import (
 	"github.com/charmbracelet/bubbles/textinput"
 	tea "github.com/charmbracelet/bubbletea"
 	"github.com/charmbracelet/lipgloss"
-	lgtree "github.com/charmbracelet/lipgloss/tree"
 	"github.com/leg100/pug/internal"
 	"github.com/leg100/pug/internal/module"
 	"github.com/leg100/pug/internal/resource"
@@ -34,16 +33,17 @@ func (mm *Maker) Make(id resource.ID, width, height int) (tui.ChildModel, error)
 		moduleService:    mm.ModuleService,
 		workspaceService: mm.WorkspaceService,
 	}
-	tree := builder.newTree("")
 	filter := textinput.New()
 	filter.Prompt = "Filter: "
+	tree, lgtree := builder.newTree("")
 	m := &model{
-		Helpers:     mm.Helpers,
-		Workdir:     mm.Workdir,
-		treeBuilder: builder,
-		tree:        tree,
-		tracker:     newTracker(tree, height),
-		filter:      filter,
+		Helpers:      mm.Helpers,
+		Workdir:      mm.Workdir,
+		treeBuilder:  builder,
+		tree:         tree,
+		renderedTree: lgtree,
+		tracker:      newTracker(tree, height),
+		filter:       filter,
 	}
 	m.common = &tui.ActionHandler{
 		Helpers:     mm.Helpers,
@@ -61,11 +61,21 @@ type model struct {
 	treeBuilder   *treeBuilder
 	tree          *tree
 	tracker       *tracker
+	renderedTree  string
 	width, height int
 	filter        textinput.Model
+	status        buildTreeStatus
 }
 
-func (m model) Init() tea.Cmd {
+type buildTreeStatus int
+
+const (
+	notBuildingTree buildTreeStatus = iota
+	buildingTree
+	queueBuildTree
+)
+
+func (m *model) Init() tea.Cmd {
 	return tea.Batch(
 		m.buildTree,
 		reload(true, m.Modules),
@@ -136,10 +146,15 @@ func (m *model) Update(msg tea.Msg) tea.Cmd {
 			return m.common.Update(msg)
 		}
 	case builtTreeMsg:
-		m.tree = (*tree)(msg)
+		m.tree = msg.tree
+		m.renderedTree = msg.rendered
 		// TODO: perform this in a cmd
 		m.tracker.reindex(m.tree, m.treeHeight())
-		return nil
+		if m.status == queueBuildTree {
+			return m.buildTree
+		} else {
+			m.status = notBuildingTree
+		}
 	case resource.Event[*module.Module]:
 		return m.buildTree
 	case resource.Event[*workspace.Workspace]:
@@ -209,12 +224,7 @@ func (m model) View() string {
 		Width(m.width - tui.ScrollbarWidth).
 		MaxWidth(m.width - tui.ScrollbarWidth).
 		Inline(true)
-	to := lgtree.New().
-		Enumerator(enumerator).
-		Indenter(indentor)
-	m.tree.render(true, to)
-	s := to.String()
-	lines := strings.Split(s, "\n")
+	lines := strings.Split(m.renderedTree, "\n")
 	numVisibleLines := clamp(m.treeHeight(), 0, len(lines))
 	visibleLines := lines[m.tracker.start : m.tracker.start+numVisibleLines]
 	for i := range visibleLines {
@@ -273,9 +283,18 @@ func (m model) BorderText() map[tui.BorderPosition]string {
 	}
 }
 
-func (m model) buildTree() tea.Msg {
-	tree := m.treeBuilder.newTree(m.filter.Value())
-	return builtTreeMsg(tree)
+func (m *model) buildTree() tea.Msg {
+	switch m.status {
+	case notBuildingTree:
+		tree, rendered := m.treeBuilder.newTree(m.filter.Value())
+		return builtTreeMsg{
+			tree:     tree,
+			rendered: rendered,
+		}
+	case buildingTree:
+		m.status = queueBuildTree
+	}
+	return nil
 }
 
 func (m model) filterVisible() bool {
diff --git a/internal/tui/explorer/nodes.go b/internal/tui/explorer/nodes.go
index d80b12a..201d2b0 100644
--- a/internal/tui/explorer/nodes.go
+++ b/internal/tui/explorer/nodes.go
@@ -11,9 +11,10 @@ import (
 
 type node interface {
 	fmt.Stringer
-
 	// ID uniquely identifies the node
 	ID() any
+	// Value returns a value for lexicographic sorting
+	Value() string
 }
 
 type dirNode struct {
@@ -26,14 +27,18 @@ func (d dirNode) ID() any {
 	return d.path
 }
 
-func (d dirNode) String() string {
+func (d dirNode) Value() string {
 	if d.root {
-		return fmt.Sprintf("%s %s", tui.DirIcon, d.path)
+		return d.path
 	} else {
-		return fmt.Sprintf("%s %s", tui.DirIcon, filepath.Base(d.path))
+		return filepath.Base(d.path)
 	}
 }
 
+func (d dirNode) String() string {
+	return fmt.Sprintf("%s %s", tui.DirIcon, d.Value())
+}
+
 type moduleNode struct {
 	id   resource.ID
 	path string
@@ -43,8 +48,12 @@ func (m moduleNode) ID() any {
 	return m.id
 }
 
+func (m moduleNode) Value() string {
+	return filepath.Base(m.path)
+}
+
 func (m moduleNode) String() string {
-	return tui.ModulePathWithIcon(filepath.Base(m.path), false)
+	return tui.ModulePathWithIcon(m.Value(), false)
 }
 
 type workspaceNode struct {
@@ -59,6 +68,10 @@ func (w workspaceNode) ID() any {
 	return w.id
 }
 
+func (w workspaceNode) Value() string {
+	return w.name
+}
+
 func (w workspaceNode) String() string {
 	name := lipgloss.NewStyle().
 		Render(w.name)
diff --git a/internal/tui/explorer/tree.go b/internal/tui/explorer/tree.go
index 5cec3b3..e3ece27 100644
--- a/internal/tui/explorer/tree.go
+++ b/internal/tui/explorer/tree.go
@@ -37,7 +37,7 @@ type treeBuilderHelpers interface {
 	WorkspaceCost(ws *workspace.Workspace) string
 }
 
-func (b *treeBuilder) newTree(filter string) *tree {
+func (b *treeBuilder) newTree(filter string) (*tree, string) {
 	t := &tree{
 		value: dirNode{root: true, path: b.wd.PrettyString()},
 	}
@@ -78,7 +78,16 @@ func (b *treeBuilder) newTree(filter string) *tree {
 			modTree.addChild(ws)
 		}
 	}
-	return t.filter(filter)
+	// Apply filter if there is one.
+	filtered := t.filter(filter)
+	// Now render the corresponding lipgloss tree. We do this here rather than
+	// in View() because it's quite expensive and thus best kept out of the
+	// bubble event loop.
+	to := lgtree.New().
+		Enumerator(enumerator).
+		Indenter(indentor)
+	filtered.render(true, to)
+	return filtered, to.String()
 }
 
 func (t *tree) filter(text string) *tree {
@@ -133,9 +142,21 @@ func (t *tree) addChild(child node) *tree {
 	}
 	newTree := &tree{value: child}
 	t.children = append(t.children, newTree)
-	// keep children lexicographically ordered
+	// keep children ordered
 	slices.SortFunc(t.children, func(a, b *tree) int {
-		if internal.StripAnsi(a.value.String()) < internal.StripAnsi(b.value.String()) {
+		// directories come before modules
+		if _, ok := a.value.(dirNode); ok {
+			if _, ok := b.value.(moduleNode); ok {
+				return -1
+			}
+		}
+		if _, ok := a.value.(moduleNode); ok {
+			if _, ok := b.value.(dirNode); ok {
+				return 1
+			}
+		}
+		// otherwise order lexicographically.
+		if a.value.Value() < b.value.Value() {
 			return -1
 		}
 		return 1
diff --git a/internal/tui/explorer/tree_test.go b/internal/tui/explorer/tree_test.go
index f744732..fbcf1fe 100644
--- a/internal/tui/explorer/tree_test.go
+++ b/internal/tui/explorer/tree_test.go
@@ -52,7 +52,7 @@ func TestTree(t *testing.T) {
 		helpers: &fakeTreeBuilderHelpers{},
 	}
 
-	got := builder.newTree("")
+	got, _ := builder.newTree("")
 
 	want := &tree{
 		value: dirNode{path: builder.wd.String(), root: true},
diff --git a/internal/tui/top/model.go b/internal/tui/top/model.go
index 7b2f3a6..0292f5b 100644
--- a/internal/tui/top/model.go
+++ b/internal/tui/top/model.go
@@ -361,7 +361,7 @@ func (m model) View() string {
 		Width(m.width).
 		Render(footer),
 	)
-	return lipgloss.JoinVertical(lipgloss.Top, components...)
+	return strings.Join(components, "\n")
 }
 
 var (
diff --git a/internal/tui/workspace/resource.go b/internal/tui/workspace/resource.go
index 83570be..ea4fd5a 100644
--- a/internal/tui/workspace/resource.go
+++ b/internal/tui/workspace/resource.go
@@ -125,19 +125,17 @@ func (m *resourceModel) View() string {
 }
 
 func (m *resourceModel) BorderText() map[tui.BorderPosition]string {
-	var tainted string
+	topLeft := fmt.Sprintf("%s %s",
+		tui.Bold.Render("resource"),
+		m.resource,
+	)
 	if m.resource.Tainted {
-		tainted = lipgloss.NewStyle().
+		topLeft += lipgloss.NewStyle().
 			Foreground(tui.Red).
-			Render("(tainted)")
+			Render(" (tainted)")
 	}
 	return map[tui.BorderPosition]string{
-		tui.TopLeftBorder: fmt.Sprintf(
-			"%s %s %s",
-			tui.Bold.Render("resource"),
-			m.resource,
-			tainted,
-		),
+		tui.TopLeftBorder: topLeft,
 	}
 }