fix(tui): keep palette highlight on the selected row when scrolled

internal/tui/palette.go

@@ -291,13 +291,14 @@ func (m *Model) palPopup() string {
 	case len(m.pal.items) == 0 && m.pal.query != "":
 		rows = append(rows, th.acDim.Render("no matches for “"+m.pal.query+"”"))
 	default:
-		for i, e := range windowEntries(m.pal.items, m.pal.sel, maxPalRows) {
+		window, start := windowEntries(m.pal.items, m.pal.sel, maxPalRows)
+		for i, e := range window {
 			prefix, label := "  ", th.acItem.Render(e.title)
 			detail := th.acDetail.Render(e.kind)
 			if e.hint != "" {
 				detail += th.acDetail.Render("  ·  ") + th.footerKey.Render(e.hint)
 			}
-			if i == m.pal.sel {
+			if start+i == m.pal.sel {
 				prefix, label = th.acSel.Render("› "), th.acSel.Render(e.title)
 			}
 			rows = append(rows, prefix+label+"  "+detail)
@@ -310,9 +311,11 @@ func (m *Model) palPopup() string {
 }
 
 // windowEntries windows entries around sel without changing indices.
-func windowEntries(entries []palEntry, sel, n int) []palEntry {
+// It returns the window and the absolute index of its first row, so
+// callers can map window-relative positions back onto sel.
+func windowEntries(entries []palEntry, sel, n int) ([]palEntry, int) {
 	if len(entries) <= n {
-		return entries
+		return entries, 0
 	}
 	start := sel - n/2
 	if start < 0 {
@@ -321,7 +324,7 @@ func windowEntries(entries []palEntry, sel, n int) []palEntry {
 	if start+n > len(entries) {
 		start = len(entries) - n
 	}
-	return entries[start : start+n]
+	return entries[start : start+n], start
 }
 
 // palHeight is the palette's rendered height (border + title + rows).

internal/tui/palette_test.go

@@ -87,6 +87,58 @@ func TestPaletteOpenFilterRun(t *testing.T) {
 	}
 }
 
+// TestPaletteSelectionTracksScroll is a regression test for the ^K popup:
+// the highlight must follow sel even after the list scrolls past the
+// visible window (the highlight used to compare a window-relative index
+// against the absolute sel, so it vanished or landed on the wrong row).
+func TestPaletteSelectionTracksScroll(t *testing.T) {
+	m := wired(t)
+	_, cmd := m.Update(key("ctrl+k"))
+	m.Update(exec(cmd)) // sessions fetch
+
+	if len(m.pal.items) <= maxPalRows {
+		t.Fatalf("fixture too small to scroll: %d entries", len(m.pal.items))
+	}
+
+	highlighted := func(m *Model) string {
+		var row string
+		n := 0
+		for _, ln := range strings.Split(plain(m.palPopup()), "\n") {
+			if strings.Contains(ln, "›") {
+				row, n = ln, n+1
+			}
+		}
+		if n != 1 {
+			t.Fatalf("expected exactly one highlighted row, got %d", n)
+		}
+		return row
+	}
+
+	// Walk the selection past the visible window; the highlight must stay
+	// on the row the selection actually points at.
+	for i := 0; i < maxPalRows+2; i++ {
+		m.Update(key("down"))
+	}
+	sel := m.pal.sel
+	if sel != maxPalRows+2 {
+		t.Fatalf("down did not advance sel: got %d", sel)
+	}
+	if row := highlighted(m); !strings.Contains(row, m.pal.items[sel].title) {
+		t.Fatalf("scrolled highlight is on the wrong row:\n%q\nwant title %q", row, m.pal.items[sel].title)
+	}
+
+	// Walk back to the top; the highlight must still track.
+	for i := 0; i < sel; i++ {
+		m.Update(key("up"))
+	}
+	if m.pal.sel != 0 {
+		t.Fatalf("up did not return to top: got %d", m.pal.sel)
+	}
+	if row := highlighted(m); !strings.Contains(row, m.pal.items[0].title) {
+		t.Fatalf("top highlight is on the wrong row:\n%q\nwant title %q", row, m.pal.items[0].title)
+	}
+}
+
 // TestPaletteFromApproval verifies the palette works from the approval rung.
 func TestPaletteFromApproval(t *testing.T) {
 	m := wired(t)