fix(tui): follow the terminal background

internal/tui/app.go

@@ -181,7 +181,7 @@ func preflightReport(checks []core.HostCheck) string {
 	return strings.Join(lines, "\n")
 }
 
-func (m model) Init() tea.Cmd { return loadVMs }
+func (m model) Init() tea.Cmd { return tea.Batch(loadVMs, tea.RequestBackgroundColor) }
 
 // Update feeds the open byo screen without consuming the message, then runs
 // the normal update.
@@ -253,6 +253,13 @@ func (m model) updateApp(msg tea.Msg) (tea.Model, tea.Cmd) {
 	}
 
 	switch msg := msg.(type) {
+	case tea.BackgroundColorMsg:
+		// The fixed palette reads as low contrast on a light terminal: every
+		// colour measured below 4.5:1 against #F7F7F7 before internal/theme
+		// grew a light set.
+		applyPalette(msg.IsDark())
+		return m, nil
+
 	case tea.WindowSizeMsg:
 		m.width, m.height = msg.Width, msg.Height
 		// A taller terminal shows more VMs before paginating; the width stays

internal/tui/theme.go

@@ -15,35 +15,60 @@ type themeColors struct {
 	accent, up, down, warn, err, dim color.Color
 }
 
-var th = themeColors{
-	accent: theme.Accent,
-	up:     theme.Up,
-	down:   theme.Down,
-	warn:   theme.Warn,
-	err:    theme.Err,
-	dim:    theme.Dim,
-}
+var th themeColors
 
 var (
-	accentStyle = lipgloss.NewStyle().Foreground(th.accent)
-	dimStyle    = lipgloss.NewStyle().Foreground(th.dim)
-	errStyle    = lipgloss.NewStyle().Foreground(th.err)
-	warnStyle   = lipgloss.NewStyle().Foreground(th.warn)
-	upStyle     = lipgloss.NewStyle().Foreground(th.up)
-	downStyle   = lipgloss.NewStyle().Foreground(th.down)
-	selStyle    = lipgloss.NewStyle().Foreground(th.accent).Bold(true)
+	accentStyle lipgloss.Style
+	dimStyle    lipgloss.Style
+	errStyle    lipgloss.Style
+	warnStyle   lipgloss.Style
+	upStyle     lipgloss.Style
+	downStyle   lipgloss.Style
+	selStyle    lipgloss.Style
 
 	// paneStyle is the one border every screen draws with: a rounded box
 	// in the theme accent, with breathing room inside. No screen builds its
 	// own lipgloss.NewStyle().Border(...); they all go through pane().
-	paneStyle = lipgloss.NewStyle().
-			Border(lipgloss.RoundedBorder()).
-			BorderForeground(th.accent).
-			Padding(1, 2)
+	paneStyle lipgloss.Style
 
-	paneTitleStyle = accentStyle.Bold(true)
+	paneTitleStyle lipgloss.Style
 )
 
+// applyPalette points every style in this package at the palette for the
+// terminal background the caller reports. Update calls it once, when Bubble
+// Tea answers the background query started in Init.
+//
+// The styles stay package-level values because 150-odd call sites read them
+// by name. One program draws with them at a time, and the switch happens
+// before the first render that follows the query.
+func applyPalette(isDark bool) {
+	p := theme.For(isDark)
+	th = themeColors{
+		accent: p.Accent,
+		up:     p.Up,
+		down:   p.Down,
+		warn:   p.Warn,
+		err:    p.Err,
+		dim:    p.Dim,
+	}
+	accentStyle = lipgloss.NewStyle().Foreground(th.accent)
+	dimStyle = lipgloss.NewStyle().Foreground(th.dim)
+	errStyle = lipgloss.NewStyle().Foreground(th.err)
+	warnStyle = lipgloss.NewStyle().Foreground(th.warn)
+	upStyle = lipgloss.NewStyle().Foreground(th.up)
+	downStyle = lipgloss.NewStyle().Foreground(th.down)
+	selStyle = lipgloss.NewStyle().Foreground(th.accent).Bold(true)
+	paneStyle = lipgloss.NewStyle().
+		Border(lipgloss.RoundedBorder()).
+		BorderForeground(th.accent).
+		Padding(1, 2)
+	paneTitleStyle = accentStyle.Bold(true)
+}
+
+// A terminal that never answers the background query keeps the dark palette,
+// which is what the unsuffixed constants in internal/theme are.
+func init() { applyPalette(true) }
+
 // paneFrame is the total width a pane() call adds on top of its content:
 // border on both sides plus the horizontal padding baked into paneStyle. A
 // caller that needs to bound a pane to the terminal width subtracts this

internal/tui/theme_test.go

@@ -0,0 +1,52 @@
+package tui
+
+import (
+	"image/color"
+	"testing"
+
+	tea "charm.land/bubbletea/v2"
+
+	"github.com/novusedge/stoat/internal/theme"
+)
+
+// applyPalette must point every style at the palette for the reported
+// background. The fixed dark set measured below 4.5:1 against a light
+// terminal for every colour, which is what internal/theme's light set fixes.
+func TestApplyPaletteFollowsTheBackground(t *testing.T) {
+	t.Cleanup(func() { applyPalette(true) })
+
+	applyPalette(false)
+	light := theme.For(false)
+	if th.accent != light.Accent {
+		t.Errorf("accent = %v, want the light palette's %v", th.accent, light.Accent)
+	}
+	if got := accentStyle.GetForeground(); got != light.Accent {
+		t.Errorf("accentStyle foreground = %v, want %v", got, light.Accent)
+	}
+	if got := paneStyle.GetBorderTopForeground(); got != light.Accent {
+		t.Errorf("pane border = %v, want %v", got, light.Accent)
+	}
+	if got := selStyle.GetForeground(); got != light.Accent {
+		t.Errorf("selStyle foreground = %v, want %v", got, light.Accent)
+	}
+
+	applyPalette(true)
+	if dark := theme.For(true); th.accent != dark.Accent {
+		t.Errorf("accent = %v, want the dark palette's %v", th.accent, dark.Accent)
+	}
+}
+
+// Bubble Tea answers the query started in Init with this message, so Update
+// has to act on it. Without the case, a light terminal keeps the dark palette
+// for the life of the program.
+func TestBackgroundColorMsgSwitchesThePalette(t *testing.T) {
+	t.Cleanup(func() { applyPalette(true) })
+
+	var m model
+	if _, cmd := m.Update(tea.BackgroundColorMsg{Color: color.White}); cmd != nil {
+		t.Errorf("the background report should not schedule work, got %T", cmd)
+	}
+	if light := theme.For(false); th.accent != light.Accent {
+		t.Errorf("a white background left accent at %v, want %v", th.accent, light.Accent)
+	}
+}