Auto-snap child viewport to bottom when typing into scrollback

Typing into a focused child while its emulator viewport was
scrolled up left the keystroke heading to the PTY but the input
box invisible below the visible region — it looked like typing
did nothing. processStdin's flushForward now sets
pendingViewportBottom whenever bytes are actually injected, so
the existing post-loop handler snaps the viewport and repaints.

Wheel events and Ctrl-B paths are untouched: both are intercepted
before reaching forward, so wheel still scrolls into history and
Ctrl-B is still the explicit escape hatch. Only bytes that would
actually reach the child PTY trigger the snap.

CHANGELOG.md

@@ -6,6 +6,29 @@ loosely follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Fixed
+- Typing into a focused child while its emulator viewport is
+  scrolled up into scrollback history now auto-snaps the viewport
+  back to the live area. Previously the keystroke reached the
+  child PTY but the input box was off-screen below the visible
+  region, so it looked like typing did nothing. Wheel scrolling
+  and Ctrl-B are unchanged; only forwarded keystrokes snap.
+- Top tab bar now keeps the top-level agent's tab highlighted
+  when focus is on one of its sub-agents (or on a Processes pane
+  entry, matching the existing agent-tree behavior). Previously
+  the tab would lose its highlight as soon as you stepped into a
+  child agent, even though you were still within that thread.
+
+### Changed
+- Sidebar rows (Processes, Agent Tree, Scratchpads) now truncate
+  overflowing names with a trailing `…` instead of spilling into
+  the main viewport. The focused row marquees its name when it
+  overflows — 1 s hold on the head, ~150 ms per cell scroll until
+  the tail is visible, 1 s hold on the tail, snap back. Row
+  position never moves while the marquee animates. When budget is
+  tight, the trailing timer indicator drops before the name
+  ellipses, since the name is the only identifier the row carries.
+
 ## [0.0.2] - 2026-05-15
 
 ### Added

internal/app/app.go

@@ -306,6 +306,28 @@ func Run(ctx context.Context, opts Options) error {
 		}
 	}()
 
+	// Marquee ticker: while a focused sidebar row's name overflows the
+	// rail width, advance the pause-scroll-pause animation by marking
+	// the sidebar dirty every marqueeStep. The chrome ticker above does
+	// the actual repaint. When no row is animating, this is a single
+	// cheap wakeup with no work.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		ticker := time.NewTicker(marqueeStep)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-ticker.C:
+			}
+			if st.marquee.active() {
+				st.markSidebarDirty()
+			}
+		}
+	}()
+
 	// External termination: SPEC §2 step 4 (SIGTERM/SIGHUP → graceful exit).
 	wg.Add(1)
 	sigCh := make(chan os.Signal, 1)
@@ -436,6 +458,11 @@ type uiState struct {
 	sidebarDirty atomic.Bool
 	chromeWake   chan struct{}
 
+	// marquee animates the focused sidebar row's name when it overflows
+	// the rail width. The dedicated 150ms ticker below flips
+	// sidebarDirty while a row is animating; idle case is free.
+	marquee marqueeState
+
 	// padsCacheMu guards the cached scratchpad listing. The sidebar
 	// and palette/sidebar nav helpers read it on every chunk-driven
 	// repaint; the cache invalidates in scratchpadsChanged() which is
@@ -476,6 +503,7 @@ func (st *uiState) focusProcess(processID string) {
 	if c == nil {
 		return
 	}
+	st.marquee.reset()
 	layout := st.layoutSnapshot()
 	onAlt := childIsOnAlt(c)
 	st.mu.Lock()
@@ -543,6 +571,7 @@ func (st *uiState) focusScratchpad(name string) {
 	if name == "" {
 		return
 	}
+	st.marquee.reset()
 	st.mu.Lock()
 	if st.padOffsetName != name {
 		st.padOffset = 0
@@ -586,6 +615,7 @@ func (st *uiState) restartFocusedCommand(processID string) {
 	if c == nil || c.Kind != KindCommand {
 		return
 	}
+	st.marquee.reset()
 	layout := st.layoutSnapshot()
 	renderer := newViewportRenderer(layout)
 	st.mu.Lock()
@@ -672,6 +702,7 @@ func (st *uiState) scratchpadsChanged() {
 
 // OnChildSpawned auto-focuses the new child.
 func (st *uiState) OnChildSpawned(c *Child) {
+	st.marquee.reset()
 	layout := st.layoutSnapshot()
 	onAlt := childIsOnAlt(c)
 	st.mu.Lock()
@@ -733,6 +764,7 @@ func (st *uiState) OnChildStateChanged(string, IdleState) {
 // focused child.
 func (st *uiState) OnChildExited(c *Child) {
 	st.lastExit.Store(int32(c.ExitCode()))
+	st.marquee.reset()
 	layout := st.layoutSnapshot()
 	renderEmpty := false
 	st.mu.Lock()
@@ -1291,6 +1323,15 @@ func (st *uiState) processStdin(chunk []byte) {
 	}
 
 	forward := make([]byte, 0, len(chunk))
+
+	var pendingAction *paletteAction
+	var pendingNav navEntry
+	var pendingRestartID string
+	var pendingViewportDelta int
+	var pendingViewportBottom bool
+	var pendingPadStep int
+	var pendingPadExit bool
+
 	flushForward := func() {
 		if len(forward) == 0 {
 			return
@@ -1305,19 +1346,16 @@ func (st *uiState) processStdin(chunk []byte) {
 				if prev != OwnerUser {
 					go st.drawStatusLine()
 				}
+				// Auto-snap the emulator viewport to the live area
+				// on any forwarded keystroke. Without this, typing
+				// while scrolled into history leaves the cursor /
+				// echoed bytes off-screen below the visible region.
+				pendingViewportBottom = true
 			}
 		}
 		forward = forward[:0]
 	}
 
-	var pendingAction *paletteAction
-	var pendingNav navEntry
-	var pendingRestartID string
-	var pendingViewportDelta int
-	var pendingViewportBottom bool
-	var pendingPadStep int
-	var pendingPadExit bool
-
 	// childOnPrimary captures whether the focused child is on its primary
 	// screen at the start of this chunk. Wheel events on the primary
 	// screen scroll the emulator viewport (inline scrollback); on the

internal/app/marquee.go

@@ -0,0 +1,123 @@
+package app
+
+import (
+	"sync"
+	"time"
+)
+
+// Phase ordering of the marquee state machine: hold the head, scroll
+// one cell per marqueeStep until the tail is visible, hold the tail,
+// snap back to the head.
+const (
+	phaseHoldStart = iota
+	phaseScroll
+	phaseHoldEnd
+)
+
+const (
+	marqueeHoldStart = time.Second
+	marqueeStep      = 150 * time.Millisecond
+	marqueeHoldEnd   = time.Second
+)
+
+// marqueeState drives the focused sidebar row's pause-scroll-pause
+// animation. State is wall-clock anchored (since), not tick-count
+// anchored, so a missed tick yields a slightly later frame rather
+// than a skipped one.
+type marqueeState struct {
+	mu      sync.Mutex
+	id      string
+	nameLen int
+	budget  int
+	state   int
+	offset  int
+	since   time.Time
+}
+
+// step advances the state machine for the row identified by id with
+// the given visible name length (in runes) and column budget. It
+// returns the current scroll offset, whether the row is animating
+// (i.e. nameLen > budget), and how long until the next visual change.
+//
+// When id changes, or nameLen <= budget, the state machine resets to
+// phaseHoldStart with offset 0 anchored at now.
+func (m *marqueeState) step(id string, nameLen, budget int, now time.Time) (offset int, animating bool, nextWake time.Duration) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if id != m.id || nameLen != m.nameLen || budget != m.budget {
+		m.id = id
+		m.nameLen = nameLen
+		m.budget = budget
+		m.state = phaseHoldStart
+		m.offset = 0
+		m.since = now
+	}
+
+	if nameLen <= budget || budget <= 0 {
+		return 0, false, 0
+	}
+
+	maxOffset := nameLen - budget
+
+	for {
+		elapsed := now.Sub(m.since)
+		switch m.state {
+		case phaseHoldStart:
+			if elapsed < marqueeHoldStart {
+				return 0, true, marqueeHoldStart - elapsed
+			}
+			m.state = phaseScroll
+			m.since = m.since.Add(marqueeHoldStart)
+			continue
+		case phaseScroll:
+			steps := int(elapsed / marqueeStep)
+			if steps >= maxOffset {
+				m.offset = maxOffset
+				m.state = phaseHoldEnd
+				m.since = m.since.Add(time.Duration(maxOffset) * marqueeStep)
+				continue
+			}
+			m.offset = steps
+			rem := marqueeStep - (elapsed % marqueeStep)
+			return m.offset, true, rem
+		case phaseHoldEnd:
+			if elapsed < marqueeHoldEnd {
+				return maxOffset, true, marqueeHoldEnd - elapsed
+			}
+			m.state = phaseHoldStart
+			m.offset = 0
+			m.since = m.since.Add(marqueeHoldEnd)
+			continue
+		default:
+			m.state = phaseHoldStart
+			m.offset = 0
+			m.since = now
+			return 0, true, marqueeHoldStart
+		}
+	}
+}
+
+// active reports whether the marquee currently has an overflowing row
+// to animate. The marquee ticker goroutine uses this to gate dirty
+// flag flips so an idle sidebar costs nothing.
+func (m *marqueeState) active() bool {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	return m.id != "" && m.nameLen > m.budget && m.budget > 0
+}
+
+// reset clears all state, forcing the next step() call to start a
+// fresh phaseHoldStart. Call this when focus changes so the newly
+// focused row begins with a full head-hold instead of inheriting
+// whatever phase the previous focus was in.
+func (m *marqueeState) reset() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.id = ""
+	m.nameLen = 0
+	m.budget = 0
+	m.state = phaseHoldStart
+	m.offset = 0
+	m.since = time.Time{}
+}

internal/app/marquee_test.go

@@ -0,0 +1,161 @@
+package app
+
+import (
+	"testing"
+	"time"
+)
+
+func TestMarqueeStepFits(t *testing.T) {
+	var m marqueeState
+	now := time.Unix(0, 0)
+	off, animating, _ := m.step("a", 5, 10, now)
+	if animating {
+		t.Fatalf("expected no animation when name fits in budget")
+	}
+	if off != 0 {
+		t.Fatalf("expected offset 0, got %d", off)
+	}
+}
+
+func TestMarqueePhaseProgression(t *testing.T) {
+	var m marqueeState
+	// name 10 runes, budget 5 → maxOffset = 5.
+	const nameLen, budget = 10, 5
+	t0 := time.Unix(0, 0)
+
+	// At t0: phaseHoldStart, offset 0, animating.
+	off, anim, wake := m.step("row", nameLen, budget, t0)
+	if off != 0 || !anim || wake != marqueeHoldStart {
+		t.Fatalf("t0: off=%d anim=%v wake=%v", off, anim, wake)
+	}
+
+	// Just before hold expires: still offset 0.
+	off, anim, _ = m.step("row", nameLen, budget, t0.Add(marqueeHoldStart-time.Millisecond))
+	if off != 0 || !anim {
+		t.Fatalf("pre-expiry hold: off=%d anim=%v", off, anim)
+	}
+
+	// At hold expiry + 1 step: should have transitioned to scroll, offset 1.
+	off, anim, _ = m.step("row", nameLen, budget, t0.Add(marqueeHoldStart+marqueeStep))
+	if !anim || off != 1 {
+		t.Fatalf("first scroll step: off=%d anim=%v", off, anim)
+	}
+
+	// Mid-scroll: offset == 3.
+	off, _, _ = m.step("row", nameLen, budget, t0.Add(marqueeHoldStart+3*marqueeStep))
+	if off != 3 {
+		t.Fatalf("mid scroll: off=%d", off)
+	}
+
+	// Tail reached: offset == maxOffset == 5.
+	off, _, _ = m.step("row", nameLen, budget, t0.Add(marqueeHoldStart+5*marqueeStep+time.Millisecond))
+	if off != 5 {
+		t.Fatalf("tail: off=%d", off)
+	}
+
+	// Hold-end window still pegged at maxOffset.
+	off, _, _ = m.step("row", nameLen, budget, t0.Add(marqueeHoldStart+5*marqueeStep+marqueeHoldEnd/2))
+	if off != 5 {
+		t.Fatalf("hold-end mid: off=%d", off)
+	}
+
+	// After hold-end: snap back to offset 0.
+	off, _, _ = m.step("row", nameLen, budget, t0.Add(marqueeHoldStart+5*marqueeStep+marqueeHoldEnd+time.Millisecond))
+	if off != 0 {
+		t.Fatalf("snap back: off=%d", off)
+	}
+}
+
+func TestMarqueeIDChangeResets(t *testing.T) {
+	var m marqueeState
+	t0 := time.Unix(0, 0)
+	_, _, _ = m.step("a", 10, 5, t0)
+	// Advance well into scroll for row "a".
+	_, _, _ = m.step("a", 10, 5, t0.Add(marqueeHoldStart+3*marqueeStep))
+	// Now focus moves to "b": offset must reset to 0 and phase to hold-start.
+	off, anim, wake := m.step("b", 10, 5, t0.Add(marqueeHoldStart+3*marqueeStep))
+	if off != 0 || !anim || wake != marqueeHoldStart {
+		t.Fatalf("id reset: off=%d anim=%v wake=%v", off, anim, wake)
+	}
+}
+
+func TestMarqueeActive(t *testing.T) {
+	var m marqueeState
+	if m.active() {
+		t.Fatalf("fresh marquee should not be active")
+	}
+	_, _, _ = m.step("row", 10, 5, time.Unix(0, 0))
+	if !m.active() {
+		t.Fatalf("expected active after overflow step")
+	}
+	_, _, _ = m.step("row", 4, 5, time.Unix(0, 0))
+	if m.active() {
+		t.Fatalf("should not be active when name fits")
+	}
+}
+
+func TestMarqueeReset(t *testing.T) {
+	var m marqueeState
+	_, _, _ = m.step("row", 10, 5, time.Unix(0, 0))
+	m.reset()
+	if m.active() {
+		t.Fatalf("expected inactive after reset")
+	}
+	// After reset, stepping the same id starts fresh.
+	off, _, wake := m.step("row", 10, 5, time.Unix(5, 0))
+	if off != 0 || wake != marqueeHoldStart {
+		t.Fatalf("post-reset start: off=%d wake=%v", off, wake)
+	}
+}
+
+func TestFitName(t *testing.T) {
+	cases := []struct {
+		name, in string
+		budget   int
+		want     string
+	}{
+		{"fits", "abc", 5, "abc"},
+		{"exact", "abcde", 5, "abcde"},
+		{"truncate", "abcdef", 5, "abcd…"},
+		{"budget1", "abcdef", 1, "…"},
+		{"budget0", "abc", 0, ""},
+		{"unicode", "αβγδεζη", 4, "αβγ…"},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			got := fitName(c.in, c.budget)
+			if got != c.want {
+				t.Fatalf("fitName(%q, %d) = %q want %q", c.in, c.budget, got, c.want)
+			}
+		})
+	}
+}
+
+func TestMarqueeWindow(t *testing.T) {
+	got := marqueeWindow("abcdefgh", 4, 2)
+	if got != "cdef" {
+		t.Fatalf("window = %q", got)
+	}
+	// Clamp end-of-string overflow.
+	got = marqueeWindow("abcdef", 4, 10)
+	if got != "cdef" {
+		t.Fatalf("clamped window = %q", got)
+	}
+}
+
+func TestClampVisible(t *testing.T) {
+	// Plain string longer than width.
+	if got := clampVisible("abcdef", 3); visibleLen(got) != 3 {
+		t.Fatalf("plain clamp visible = %d (%q)", visibleLen(got), got)
+	}
+	// Already-fitting string is unchanged.
+	if got := clampVisible("abc", 5); got != "abc" {
+		t.Fatalf("unchanged = %q", got)
+	}
+	// SGR-wrapped string: visible portion must be <= width.
+	in := "\x1b[1mhello\x1b[0m world"
+	got := clampVisible(in, 5)
+	if visibleLen(got) != 5 {
+		t.Fatalf("sgr clamp visible = %d (%q)", visibleLen(got), got)
+	}
+}

internal/app/sidebar.go

@@ -12,6 +12,128 @@ const (
 	statusRows  = 1
 )
 
+// fitName returns name truncated to fit budget visible cells, with a
+// trailing "…" when it overflows. Operates on RAW (unstyled) input;
+// the caller wraps the result in SGR. Returns "" when budget <= 0.
+func fitName(name string, budget int) string {
+	if budget <= 0 {
+		return ""
+	}
+	runes := []rune(name)
+	if len(runes) <= budget {
+		return name
+	}
+	if budget == 1 {
+		return "…"
+	}
+	return string(runes[:budget-1]) + "…"
+}
+
+// marqueeWindow returns the window of name starting at offset, exactly
+// budget cells wide. Pre: caller has decided the name overflows budget
+// and offset is in [0, len([]rune(name))-budget]. Operates on RAW
+// (unstyled) input.
+func marqueeWindow(name string, budget, offset int) string {
+	if budget <= 0 {
+		return ""
+	}
+	runes := []rune(name)
+	if len(runes) <= budget {
+		return name
+	}
+	if offset < 0 {
+		offset = 0
+	}
+	end := offset + budget
+	if end > len(runes) {
+		end = len(runes)
+		offset = end - budget
+		if offset < 0 {
+			offset = 0
+		}
+	}
+	return string(runes[offset:end])
+}
+
+// clampVisible truncates s so that its visible (non-SGR) length is at
+// most width cells, preserving any active style by appending a reset.
+// Used as a defensive net by write() so a row whose decoration was
+// mis-sized still cannot spill past the sidebar band into the PTY area.
+func clampVisible(s string, width int) string {
+	if width <= 0 {
+		return ""
+	}
+	if visibleLen(s) <= width {
+		return s
+	}
+	var b strings.Builder
+	b.Grow(len(s))
+	visible := 0
+	inEsc := false
+	for _, r := range s {
+		if inEsc {
+			b.WriteRune(r)
+			if r == 'm' || r == 'H' {
+				inEsc = false
+			}
+			continue
+		}
+		if r == 0x1b {
+			inEsc = true
+			b.WriteRune(r)
+			continue
+		}
+		if visible >= width {
+			break
+		}
+		b.WriteRune(r)
+		visible++
+	}
+	b.WriteString(styleReset)
+	return b.String()
+}
+
+// chooseSidebarSuffix decides whether to keep or drop the trailing
+// timer indicator from a sidebar row's suffix. When the row's name
+// would have to ellipsise with the timer present, but the budget
+// freed by dropping the timer still leaves at least 6 cells for the
+// name, the timer is dropped. The name is the only identifier the
+// user has for that row; the timer is recoverable from the status
+// line and palette.
+func chooseSidebarSuffix(nameRuneLen, width int, prefix, suffix, timer string) (string, int) {
+	prefixCost := visibleLen(prefix)
+	budget := width - prefixCost - visibleLen(suffix)
+	if nameRuneLen <= budget || timer == "" {
+		return suffix, budget
+	}
+	slim := strings.TrimSuffix(suffix, timer)
+	if slim == suffix {
+		return suffix, budget
+	}
+	slimBudget := width - prefixCost - visibleLen(slim)
+	if slimBudget >= 6 {
+		return slim, slimBudget
+	}
+	return suffix, budget
+}
+
+// rowNameSlot returns the unstyled name cell for a sidebar row.
+// Unfocused (or focused-and-fitting) rows get fitName with a trailing
+// "…" on overflow. The focused row, when its name overflows the
+// budget, gets the current marquee window — exactly budget cells
+// wide so the surrounding row geometry stays put while it animates.
+func (st *uiState) rowNameSlot(id, rawName string, budget int, focused bool) string {
+	if budget <= 0 {
+		return ""
+	}
+	runes := []rune(rawName)
+	if !focused || len(runes) <= budget {
+		return fitName(rawName, budget)
+	}
+	off, _, _ := st.marquee.step(id, len(runes), budget, time.Now())
+	return marqueeWindow(rawName, budget, off)
+}
+
 // formatShortDuration renders a duration as a short, sidebar-friendly
 // suffix: ms under 1s, "12s" under 60s, "3m" otherwise.
 func formatShortDuration(d time.Duration) string {
@@ -73,6 +195,9 @@ func (st *uiState) drawSidebar() {
 		if row > maxRow {
 			return
 		}
+		if visibleLen(content) > width {
+			content = clampVisible(content, width)
+		}
 		pad := width - visibleLen(content)
 		if pad < 0 {
 			pad = 0
@@ -154,14 +279,19 @@ func (st *uiState) drawSidebar() {
 		if c.AutoRestart() {
 			marker = " " + styleDim + "⟳" + styleReset
 		}
-		var line string
+		timer := timerIndicator(c)
+		var prefix, openStyle string
 		if focused {
-			line = " " + styleAccent + "▎" + styleReset + " " + glyph + " " +
+			prefix = " " + styleAccent + "▎" + styleReset + " " + glyph + " "
-				styleBold + c.DisplayName() + styleReset + marker + timerIndicator(c)
+			openStyle = styleBold
 		} else {
-			line = "   " + glyph + " " + styleHint + c.DisplayName() + styleReset + marker + timerIndicator(c)
+			prefix = "   " + glyph + " "
+			openStyle = styleHint
 		}
-		write(line)
+		raw := c.DisplayName()
+		suffix, budget := chooseSidebarSuffix(len([]rune(raw)), width, prefix, marker+timer, timer)
+		nameCell := st.rowNameSlot(c.ID, raw, budget, focused)
+		write(prefix + openStyle + nameCell + styleReset + suffix)
 	}
 
 	// Agent Tree section — formerly "Session tree". Shows the active
@@ -186,14 +316,19 @@ func (st *uiState) drawSidebar() {
 		}
 		focused := c.ID == focus
 		glyph := statusGlyph(c, focused)
-		var line string
+		timer := timerIndicator(c)
+		var prefix, openStyle string
 		if focused {
-			line = " " + styleAccent + "▎" + styleReset + " " + indent + glyph + " " +
+			prefix = " " + styleAccent + "▎" + styleReset + " " + indent + glyph + " "
-				styleBold + c.DisplayName() + styleReset + timerIndicator(c)
+			openStyle = styleBold
 		} else {
-			line = "   " + indent + glyph + " " + styleHint + c.DisplayName() + styleReset + timerIndicator(c)
+			prefix = "   " + indent + glyph + " "
+			openStyle = styleHint
 		}
-		write(line)
+		raw := c.DisplayName()
+		suffix, budget := chooseSidebarSuffix(len([]rune(raw)), width, prefix, timer, timer)
+		nameCell := st.rowNameSlot(c.ID, raw, budget, focused)
+		write(prefix + openStyle + nameCell + styleReset + suffix)
 	}
 
 	// Scratchpads list — names only. The preview pane used to live
@@ -212,14 +347,18 @@ func (st *uiState) drawSidebar() {
 					if row > maxRow {
 						break
 					}
-					var line string
+					focused := e.Name == focusPad
-					if e.Name == focusPad {
+					var prefix, openStyle string
-						line = " " + styleAccent + "▎" + styleReset + " " +
+					if focused {
-							styleBold + e.Name + styleReset
+						prefix = " " + styleAccent + "▎" + styleReset + " "
+						openStyle = styleBold
 					} else {
-						line = "   " + styleHint + e.Name + styleReset
+						prefix = "   "
+						openStyle = styleHint
 					}
-					write(line)
+					budget := width - visibleLen(prefix)
+					nameCell := st.rowNameSlot("pad:"+e.Name, e.Name, budget, focused)
+					write(prefix + openStyle + nameCell + styleReset)
 				}
 			}
 		}

internal/app/tabbar.go

@@ -24,7 +24,11 @@ func (st *uiState) drawTabBar() {
 	}
 	st.mu.Lock()
 	palOpen := st.palette != nil
-	focus := st.focusedID
+	// Highlight the top-level agent tab even when focus has stepped
+	// into a sub-agent (or a Processes pane entry). activeAgentID walks
+	// the parent chain to the root, so the user always sees which tab
+	// their current thread belongs to.
+	focus := st.activeAgentID
 	st.mu.Unlock()
 	if palOpen {
 		return