feat(tui): dock approval gate + two-column diff viewer

Replace the floating approval modal (which blanked the whole UI) with an
opencode-style band that takes the input bar's slot while a gate is
pending: tool/tier/risk header above a side-by-side old|new diff, with
the session output and event stream still visible above it. The band
height adapts to the diff length.

Add a unified-diff parser that aligns removals/additions into split rows
(blank left cell for a create, blank right for a delete) and a
two-column renderer shared by the band preview and the ^x fullscreen
view. Wire plain a/r to approve/reject to match the advertised keys.

apps/tui-go/internal/app/diff.go

@@ -0,0 +1,184 @@
+package app
+
+import (
+	"strconv"
+	"strings"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+type diffKind int
+
+const (
+	diffBlank diffKind = iota // no line on this side
+	diffContext
+	diffDel
+	diffAdd
+)
+
+// diffRow is one aligned row of a split (side-by-side) diff: the old line on the
+// left, the new line on the right. Either side may be blank (pure add/remove).
+type diffRow struct {
+	oldNum, newNum   int // 0 = blank cell
+	oldText, newText string
+	oldKind, newKind diffKind
+}
+
+// parseUnifiedDiff turns a unified diff into aligned old|new rows. File headers
+// (---, +++, diff, index) are dropped; @@ markers seed the line numbers.
+// Consecutive removals and additions are zipped so an edit lines up; a pure
+// create yields blank left cells (and vice-versa for a delete).
+func parseUnifiedDiff(diff string) []diffRow {
+	var rows []diffRow
+	oldN, newN := 1, 1
+	var dels, adds []string
+	flush := func() {
+		n := len(dels)
+		if len(adds) > n {
+			n = len(adds)
+		}
+		for i := 0; i < n; i++ {
+			r := diffRow{}
+			if i < len(dels) {
+				r.oldNum, r.oldText, r.oldKind = oldN, dels[i], diffDel
+				oldN++
+			}
+			if i < len(adds) {
+				r.newNum, r.newText, r.newKind = newN, adds[i], diffAdd
+				newN++
+			}
+			rows = append(rows, r)
+		}
+		dels, adds = dels[:0], adds[:0]
+	}
+	for _, ln := range strings.Split(strings.TrimRight(diff, "\n"), "\n") {
+		switch {
+		case strings.HasPrefix(ln, "+++"), strings.HasPrefix(ln, "---"),
+			strings.HasPrefix(ln, "diff "), strings.HasPrefix(ln, "index "):
+			continue
+		case strings.HasPrefix(ln, "@@"):
+			flush()
+			oldN, newN = hunkStarts(ln)
+		case strings.HasPrefix(ln, "-"):
+			dels = append(dels, ln[1:])
+		case strings.HasPrefix(ln, "+"):
+			adds = append(adds, ln[1:])
+		default: // context (leading space) or stray blank line
+			flush()
+			text := strings.TrimPrefix(ln, " ")
+			rows = append(rows, diffRow{
+				oldNum: oldN, newNum: newN, oldText: text, newText: text,
+				oldKind: diffContext, newKind: diffContext,
+			})
+			oldN++
+			newN++
+		}
+	}
+	flush()
+	return rows
+}
+
+// hunkStarts reads the starting old/new line numbers from an @@ -a,b +c,d @@ marker.
+func hunkStarts(h string) (int, int) {
+	old, newer := 1, 1
+	for _, f := range strings.Fields(h) {
+		switch {
+		case strings.HasPrefix(f, "-"):
+			old = atoiComma(f[1:])
+		case strings.HasPrefix(f, "+"):
+			newer = atoiComma(f[1:])
+		}
+	}
+	return old, newer
+}
+
+func atoiComma(s string) int {
+	if i := strings.IndexByte(s, ','); i >= 0 {
+		s = s[:i]
+	}
+	n, _ := strconv.Atoi(s)
+	return n
+}
+
+// diffTarget returns the path the diff writes to (the +++ side), stripped of the
+// b/ prefix. Empty if the diff carries no header.
+func diffTarget(diff string) string {
+	for _, ln := range strings.Split(diff, "\n") {
+		if strings.HasPrefix(ln, "+++ ") {
+			p := strings.Fields(strings.TrimPrefix(ln, "+++ "))[0]
+			p = strings.TrimPrefix(p, "b/")
+			if p != "/dev/null" {
+				return p
+			}
+		}
+	}
+	return ""
+}
+
+const diffGutter = 4 // line-number column width
+
+// renderSplitDiff renders aligned rows as a two-column old|new view exactly
+// `width` cells wide, returning up to maxRows lines starting at offset off.
+func (m Model) renderSplitDiff(rows []diffRow, width, maxRows, off int) []string {
+	colW := (width - 1) / 2
+	if colW < diffGutter+4 {
+		colW = diffGutter + 4
+	}
+	if off < 0 {
+		off = 0
+	}
+	if off > len(rows) {
+		off = len(rows)
+	}
+	end := off + maxRows
+	if end > len(rows) {
+		end = len(rows)
+	}
+	sep := lipgloss.NewStyle().Foreground(m.theme.P.Border).Background(m.theme.P.Bg).Render("│")
+	out := make([]string, 0, end-off)
+	for _, r := range rows[off:end] {
+		out = append(out,
+			m.diffCell(r.oldNum, r.oldText, r.oldKind, colW)+sep+
+				m.diffCell(r.newNum, r.newText, r.newKind, colW))
+	}
+	return out
+}
+
+// diffCell renders one side of a diff row (gutter number, +/- sign, text) padded
+// to width w with the kind's background tint.
+func (m Model) diffCell(num int, text string, kind diffKind, w int) string {
+	t := m.theme
+	if kind == diffBlank {
+		return lipgloss.NewStyle().Background(t.P.Bg).Render(strings.Repeat(" ", w))
+	}
+	var bg, textFg, signFg lipgloss.Color
+	sign := " "
+	switch kind {
+	case diffAdd:
+		bg, textFg, signFg, sign = t.P.DiffAdd, t.P.FgStrong, t.P.OK, "+"
+	case diffDel:
+		bg, textFg, signFg, sign = t.P.DiffDel, t.P.FgStrong, t.P.Bad, "-"
+	default: // context
+		bg, textFg, signFg = t.P.Bg, t.P.Dim, t.P.Faint
+	}
+	numStr := ""
+	if num > 0 {
+		numStr = itoa(num)
+	}
+	numCell := lipgloss.NewStyle().Foreground(t.P.Faint).Background(bg).Render(padLeft(numStr, diffGutter) + " ")
+	signCell := lipgloss.NewStyle().Foreground(signFg).Background(bg).Bold(true).Render(sign + " ")
+	textW := w - diffGutter - 3
+	if textW < 1 {
+		textW = 1
+	}
+	body := lipgloss.NewStyle().Foreground(textFg).Background(bg).Render(truncate(text, textW))
+	return padTo(numCell+signCell+body, w, bg)
+}
+
+// padLeft right-aligns s in a field of width w (space-padded on the left).
+func padLeft(s string, w int) string {
+	if len(s) >= w {
+		return s
+	}
+	return strings.Repeat(" ", w-len(s)) + s
+}

apps/tui-go/internal/app/diff_test.go

@@ -0,0 +1,53 @@
+package app
+
+import "testing"
+
+func TestParseUnifiedDiff_Create(t *testing.T) {
+	diff := "--- /dev/null\n+++ b/hello.sh\n@@ -0,0 +1,2 @@\n+#!/usr/bin/env bash\n+echo hi\n"
+	rows := parseUnifiedDiff(diff)
+	if len(rows) != 2 {
+		t.Fatalf("want 2 rows, got %d", len(rows))
+	}
+	for i, r := range rows {
+		if r.oldKind != diffBlank || r.oldNum != 0 || r.oldText != "" {
+			t.Errorf("row %d: create should have a blank left cell, got %+v", i, r)
+		}
+		if r.newKind != diffAdd {
+			t.Errorf("row %d: right cell should be an addition, got %+v", i, r)
+		}
+	}
+	if rows[0].newNum != 1 || rows[1].newNum != 2 {
+		t.Errorf("new line numbers should start at 1: %d, %d", rows[0].newNum, rows[1].newNum)
+	}
+}
+
+func TestParseUnifiedDiff_EditAlignsAndNumbers(t *testing.T) {
+	diff := "--- a/x\n+++ b/x\n@@ -1,3 +1,3 @@\n ctx\n-old\n+new\n more\n"
+	rows := parseUnifiedDiff(diff)
+	if len(rows) != 3 {
+		t.Fatalf("want 3 rows (context, change, context), got %d", len(rows))
+	}
+	// context row: both sides present, same text, line 1
+	if rows[0].oldNum != 1 || rows[0].newNum != 1 || rows[0].oldText != "ctx" || rows[0].newText != "ctx" {
+		t.Errorf("context row mis-numbered/aligned: %+v", rows[0])
+	}
+	// change row: old "old" on left, new "new" on right, both line 2
+	c := rows[1]
+	if c.oldKind != diffDel || c.newKind != diffAdd || c.oldText != "old" || c.newText != "new" {
+		t.Errorf("change row should pair del|add: %+v", c)
+	}
+	if c.oldNum != 2 || c.newNum != 2 {
+		t.Errorf("change row line numbers should be 2/2: %d/%d", c.oldNum, c.newNum)
+	}
+	// trailing context advances to line 3 on both sides
+	if rows[2].oldNum != 3 || rows[2].newNum != 3 {
+		t.Errorf("trailing context should be 3/3: %d/%d", rows[2].oldNum, rows[2].newNum)
+	}
+}
+
+func TestDiffTarget(t *testing.T) {
+	got := diffTarget("--- a/old.sh\n+++ b/dir/new.sh\n@@ -0,0 +1 @@\n+x\n")
+	if got != "dir/new.sh" {
+		t.Errorf("diffTarget = %q, want dir/new.sh", got)
+	}
+}

apps/tui-go/internal/app/overlays.go

@@ -52,15 +52,38 @@ func mbg(t Theme, s string, fg lipgloss.Color) string {
 	return lipgloss.NewStyle().Foreground(fg).Background(t.P.BgPanel).Render(s)
 }
 
-func (m Model) renderApproval(base string) string {
+// approvalBandHeight sizes the docked approval band to its diff, capped so it
+// never crowds out the session above (longer diffs spill to the ^x fullscreen
+// view). Layout: 2 borders + header + blank + diff rows + blank + action row.
+func (m Model) approvalBandHeight() int {
+	rows := 0
+	if s := m.session(m.selectedID); s != nil && s.Pending != nil {
+		rows = len(parseUnifiedDiff(s.Pending.Preview))
+	}
+	h := 2 + 1 + 1 + rows + 1 + 1
+	if maxH := m.height * 55 / 100; h > maxH {
+		h = maxH
+	}
+	if h < 10 {
+		h = 10
+	}
+	if hardMax := m.height - statusH - footerH - 3; hardMax > 4 && h > hardMax {
+		h = hardMax
+	}
+	return h
+}
+
+// renderApprovalBand draws the approval gate as a full-width band (in place of
+// the input bar): tool/tier/risk header, a two-column old|new diff, and the
+// action row. It never floats over the rest of the UI.
+func (m Model) renderApprovalBand(h int) string {
 	t := m.theme
 	s := m.session(m.selectedID)
 	if s == nil || s.Pending == nil {
-		return base
+		return m.renderInput()
 	}
 	a := s.Pending
-	w := m.modalWidth()
-	textW := w - 6
+	textW := m.width - 4 // box borders (2) + side padding (2)
 
 	riskColor := t.P.Warn
 	switch strings.ToUpper(a.Risk) {
@@ -70,28 +93,51 @@ func (m Model) renderApproval(base string) string {
 		riskColor = t.P.OK
 	}
 
-	var b strings.Builder
-	b.WriteString(m.titleLine("approval required") + "\n\n")
-	b.WriteString(mbg(t, "tool   ", t.P.Faint) + mbg(t, a.ToolName, t.P.FgStrong) + "\n")
-	b.WriteString(mbg(t, "tier   ", t.P.Faint) + mbg(t, a.Tier, t.P.Accent2) + "\n")
-	b.WriteString(mbg(t, "risk   ", t.P.Faint) + lipgloss.NewStyle().Foreground(riskColor).Background(t.P.BgPanel).Bold(true).Render(strings.ToUpper(a.Risk)) + "\n")
-	if a.Preview != "" {
-		b.WriteString("\n" + mbg(t, "preview", t.P.Faint) + "\n")
-		for _, ln := range limitLines(a.Preview, 6) {
-			b.WriteString(mbg(t, "  "+truncate(ln, textW), t.P.Dim) + "\n")
-		}
+	leftHdr := lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Bold(true).Render("→ ") +
+		t.span(a.ToolName, t.P.FgStrong)
+	if tgt := diffTarget(a.Preview); tgt != "" {
+		leftHdr += t.span(" "+tgt, t.P.Dim)
 	}
-	b.WriteString("\n" + mbg(t, "steer  ", t.P.Faint))
-	if m.steerBuffer == "" {
-		b.WriteString(mbg(t, "(optional note)", t.P.Faint))
-	} else {
-		b.WriteString(mbg(t, m.steerBuffer, t.P.FgStrong))
-	}
-	b.WriteString(lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.BgPanel).Render("▏") + "\n\n")
-	b.WriteString(modalHints(t, [][2]string{{"^a", "approve"}, {"^r", "reject"}, {"s", "steer"}, {"enter", "approve"}, {"^x", "diff"}, {"esc", "later"}}))
+	rightHdr := t.span("tier ", t.P.Faint) + t.span(a.Tier, t.P.Accent2) +
+		t.span("  ·  risk ", t.P.Faint) +
+		lipgloss.NewStyle().Foreground(riskColor).Background(t.P.Bg).Bold(true).Render(strings.ToUpper(a.Risk))
 
-	modal := t.Overlay.Width(w).Render(b.String())
-	return m.center(modal)
+	innerH := h - 2
+	diffH := innerH - 4 // header, blank, blank, action row
+	if diffH < 1 {
+		diffH = 1
+	}
+	rows := parseUnifiedDiff(a.Preview)
+
+	body := make([]string, 0, innerH)
+	body = append(body, m.justify(leftHdr, rightHdr, textW, t.P.Bg), "")
+	body = append(body, m.renderSplitDiff(rows, textW, diffH, 0)...)
+	for len(body) < 2+diffH {
+		body = append(body, "")
+	}
+	body = append(body, "", m.approvalActions())
+	return t.box("permission required", body, m.width, h, true)
+}
+
+// approvalActions renders the action row of the approval band, or the live steer
+// note when the operator is composing one.
+func (m Model) approvalActions() string {
+	t := m.theme
+	if m.steering {
+		note, fg := m.steerBuffer, t.P.FgStrong
+		if note == "" {
+			note, fg = "(steer note — enter to send, esc to cancel)", t.P.Faint
+		}
+		return t.span("steer ", t.P.Faint) + t.span(note, fg) +
+			lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Render("▏")
+	}
+	hint := func(k, l string) string {
+		return lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Bold(true).Render(k) +
+			t.span(" "+l, t.P.Faint)
+	}
+	parts := []string{hint("a", "approve"), hint("A", "auto"), hint("s", "steer"),
+		hint("r", "reject"), hint("^x", "fullscreen"), hint("esc", "later")}
+	return strings.Join(parts, t.span("   ", t.P.Faint))
 }
 
 // diffBodyHeight is the number of diff lines visible in the diff modal body.
@@ -104,10 +150,10 @@ func (m Model) diffBodyHeight() int {
 }
 
 // diffMaxScroll is the largest scroll offset that still fills the body with
-// diff lines, keeping the last page anchored to the bottom of the modal.
+// diff rows, keeping the last page anchored to the bottom of the modal.
 func (m Model) diffMaxScroll() int {
-	lines := strings.Split(strings.TrimRight(m.currentDiff(), "\n"), "\n")
-	max := len(lines) - m.diffBodyHeight()
+	rows := parseUnifiedDiff(m.currentDiff())
+	max := len(rows) - m.diffBodyHeight()
 	if max < 0 {
 		max = 0
 	}
@@ -119,7 +165,7 @@ func (m Model) diffModal() string {
 	w := m.modalWidth()
 	bodyH := m.diffBodyHeight()
 	diff := m.currentDiff()
-	lines := strings.Split(strings.TrimRight(diff, "\n"), "\n")
+	rows := parseUnifiedDiff(diff)
 
 	off := m.diffScrollOffset
 	if off > m.diffMaxScroll() {
@@ -128,24 +174,15 @@ func (m Model) diffModal() string {
 	if off < 0 {
 		off = 0
 	}
-	end := off + bodyH
-	if end > len(lines) {
-		end = len(lines)
-	}
 
 	var b strings.Builder
-	b.WriteString(m.titleLine("diff") + mbg(t, "   ("+itoa(len(lines))+" lines)", t.P.Faint) + "\n\n")
-	for _, ln := range lines[off:end] {
-		fg := t.P.Dim
-		switch {
-		case strings.HasPrefix(ln, "+"):
-			fg = t.P.OK
-		case strings.HasPrefix(ln, "-"):
-			fg = t.P.Bad
-		case strings.HasPrefix(ln, "@@"):
-			fg = t.P.Accent2
-		}
-		b.WriteString(mbg(t, truncate(ln, w-6), fg) + "\n")
+	b.WriteString(m.titleLine("diff"))
+	if tgt := diffTarget(diff); tgt != "" {
+		b.WriteString(mbg(t, "  "+tgt, t.P.Dim))
+	}
+	b.WriteString(mbg(t, "   ("+itoa(len(rows))+" rows)", t.P.Faint) + "\n\n")
+	for _, ln := range m.renderSplitDiff(rows, w-6, bodyH, off) {
+		b.WriteString(ln + "\n")
 	}
 	b.WriteString("\n" + modalHints(t, [][2]string{{"↑↓", "scroll"}, {"^x/esc", "close"}}))
 
@@ -316,14 +353,6 @@ func modalHints(t Theme, pairs [][2]string) string {
 	return strings.Join(parts, mbg(t, "   ", t.P.Faint))
 }
 
-func limitLines(s string, n int) []string {
-	lines := strings.Split(strings.TrimRight(s, "\n"), "\n")
-	if len(lines) > n {
-		lines = lines[:n]
-	}
-	return lines
-}
-
 func truncate(s string, w int) string {
 	if len([]rune(s)) <= w {
 		return s

apps/tui-go/internal/app/theme.go

@@ -5,23 +5,26 @@ import "github.com/charmbracelet/lipgloss"
 // Palette is the "Soft" chrome from docs/visual/ref with the blue accent:
 // rounded borders, opaque dark panels, generous spacing.
 type Palette struct {
-	Bg        lipgloss.Color // panel/background fill
-	BgDeep    lipgloss.Color // outermost backdrop (slightly darker)
-	BgPanel   lipgloss.Color // inside-panel fill
-	Sel       lipgloss.Color // selection row background
-	Border    lipgloss.Color // idle panel border
-	BorderHi  lipgloss.Color // active panel border
-	Fg        lipgloss.Color // primary text
-	FgStrong  lipgloss.Color // headings / emphasis
-	Dim       lipgloss.Color // labels, secondary text
-	Faint     lipgloss.Color // tertiary, hints
-	Accent    lipgloss.Color // blue accent
-	Accent2   lipgloss.Color // secondary accent
+	Bg       lipgloss.Color // panel/background fill
+	BgDeep   lipgloss.Color // outermost backdrop (slightly darker)
+	BgPanel  lipgloss.Color // inside-panel fill
+	Sel      lipgloss.Color // selection row background
+	Border   lipgloss.Color // idle panel border
+	BorderHi lipgloss.Color // active panel border
+	Fg       lipgloss.Color // primary text
+	FgStrong lipgloss.Color // headings / emphasis
+	Dim      lipgloss.Color // labels, secondary text
+	Faint    lipgloss.Color // tertiary, hints
+	Accent   lipgloss.Color // blue accent
+	Accent2  lipgloss.Color // secondary accent
 
 	OK   lipgloss.Color
 	Warn lipgloss.Color
 	Bad  lipgloss.Color
 
+	DiffAdd lipgloss.Color // added-line cell background
+	DiffDel lipgloss.Color // removed-line cell background
+
 	CatLifecycle lipgloss.Color
 	CatContext   lipgloss.Color
 	CatInference lipgloss.Color
@@ -50,6 +53,9 @@ var SoftBlue = Palette{
 	Warn: lipgloss.Color("#e8c06a"),
 	Bad:  lipgloss.Color("#e87f7f"),
 
+	DiffAdd: lipgloss.Color("#1b2a1d"),
+	DiffDel: lipgloss.Color("#2c1c1f"),
+
 	CatLifecycle: lipgloss.Color("#c98fd9"),
 	CatContext:   lipgloss.Color("#b9c0c9"),
 	CatInference: lipgloss.Color("#56c8d8"),
@@ -69,17 +75,17 @@ type Theme struct {
 	PanelTitle lipgloss.Style // uppercase dim header label
 	TitleHi    lipgloss.Style // active header label
 
-	Text     lipgloss.Style
-	Strong   lipgloss.Style
-	Dim      lipgloss.Style
-	Faint    lipgloss.Style
-	Accent   lipgloss.Style
-	SelRow   lipgloss.Style
-	Status   lipgloss.Style // top bar
-	Footer   lipgloss.Style // bottom hints
-	Input    lipgloss.Style // input bar panel
-	Overlay  lipgloss.Style // modal box
-	Scrim    lipgloss.Style // dim backdrop behind modals
+	Text    lipgloss.Style
+	Strong  lipgloss.Style
+	Dim     lipgloss.Style
+	Faint   lipgloss.Style
+	Accent  lipgloss.Style
+	SelRow  lipgloss.Style
+	Status  lipgloss.Style // top bar
+	Footer  lipgloss.Style // bottom hints
+	Input   lipgloss.Style // input bar panel
+	Overlay lipgloss.Style // modal box
+	Scrim   lipgloss.Style // dim backdrop behind modals
 }
 
 // NewTheme builds the style set for a palette.

apps/tui-go/internal/app/update.go

@@ -195,11 +195,18 @@ func (m Model) handleNormalKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 			m.client.Send(protocol.CancelSession(m.selectedID))
 		}
 	case "a":
+		if ds == StateApproval {
+			return m.decide("APPROVE")
+		}
 		if ds == StateInSession {
 			if s := m.session(m.selectedID); s != nil && s.Pending != nil {
 				m.approvalDismissed = false
 			}
 		}
+	case "r":
+		if ds == StateApproval {
+			return m.decide("REJECT")
+		}
 	case "A":
 		if ds == StateApproval {
 			return m.autoApprove()

apps/tui-go/internal/app/view.go

@@ -22,7 +22,14 @@ func (m Model) View() string {
 		return m.theme.Screen.Render("correx — terminal too small")
 	}
 
-	mainH := m.height - statusH - footerH - inputH
+	bottom := m.renderInput()
+	bottomH := inputH
+	if m.displayState() == StateApproval {
+		bottomH = m.approvalBandHeight()
+		bottom = m.renderApprovalBand(bottomH)
+	}
+
+	mainH := m.height - statusH - footerH - bottomH
 	if mainH < 3 {
 		mainH = 3
 	}
@@ -30,16 +37,13 @@ func (m Model) View() string {
 	base := lipgloss.JoinVertical(lipgloss.Left,
 		m.renderStatus(),
 		m.renderMain(mainH),
-		m.renderInput(),
+		bottom,
 		m.renderFooter(),
 	)
 
 	if m.overlay != OverlayNone {
 		return m.renderOverlay(base)
 	}
-	if m.displayState() == StateApproval {
-		return m.renderApproval(base)
-	}
 	return base
 }