fix(cli): align the picker title border with the panel width

Measure the rendered panel instead of assuming panelWidth+2 — the
replacement top border was one column wider than the panel.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: jmelahman

cli/20260821_18h11m09s_grim.png

@@ -1,8 +1,10 @@
 package tui
 
 import (
+	"strings"
 	"testing"
 
+	"charm.land/lipgloss/v2"
 	"github.com/onyx-dot-app/onyx/cli/internal/config"
 	"github.com/onyx-dot-app/onyx/cli/internal/models"
 )
@@ -141,6 +143,31 @@ func TestSelectModelSetsOverrideAndStatus(t *testing.T) {
 	}
 }
 
+func TestPickerBorderLinesShareOneWidth(t *testing.T) {
+	v := newViewport(120, false)
+	v.showPicker(pickerModel, []pickerItem{
+		{id: "0", label: "Gemma 4 E2B - Ollama *"},
+		{id: "1", label: "Qwen 3 8B - Ollama"},
+	})
+
+	var widths []int
+	for _, line := range strings.Split(v.renderPicker(120, 30), "\n") {
+		trimmed := strings.TrimRight(line, " ")
+		if strings.TrimSpace(stripANSI(trimmed)) == "" {
+			continue
+		}
+		widths = append(widths, lipgloss.Width(trimmed))
+	}
+	if len(widths) == 0 {
+		t.Fatal("expected rendered panel lines")
+	}
+	for i, w := range widths {
+		if w != widths[0] {
+			t.Errorf("panel line %d width = %d, want %d (title border must match the panel)", i, w, widths[0])
+		}
+	}
+}
+
 func TestSelectModelInvalidIndex(t *testing.T) {
 	m := NewModel(config.DefaultConfig(), nil)
 	m, _ = cmdSelectModel(m, "5")

cli/internal/tui/commands_test.go

@@ -353,18 +353,20 @@ func (v *viewport) renderPicker(width, height int) string {
 		Bold(true).
 		Render(" " + title + " ")
 
-	// Build top border manually to avoid ANSI-corrupted rune slicing.
-	// panelWidth+2 accounts for the left and right border characters.
+	// Build top border manually to avoid ANSI-corrupted rune slicing. Measure
+	// the rendered panel instead of assuming its width — lipgloss box sizing
+	// would put the replacement line off by one.
+	panelLines := strings.Split(panel, "\n")
+	panelTotalWidth := lipgloss.Width(panelLines[len(panelLines)-1])
 	borderColor := lipgloss.NewStyle().Foreground(accentColor)
 	titleWidth := lipgloss.Width(titleRendered)
-	rightDashes := panelWidth + 2 - 3 - titleWidth // total - "╭─" - "╮" - title
+	rightDashes := panelTotalWidth - 3 - titleWidth // total - "╭─" - "╮" - title
 	if rightDashes < 0 {
 		rightDashes = 0
 	}
 	topBorder := borderColor.Render("╭─") + titleRendered +
 		borderColor.Render(strings.Repeat("─", rightDashes)+"╮")
 
-	panelLines := strings.Split(panel, "\n")
 	if len(panelLines) > 0 {
 		panelLines[0] = topBorder
 	}