dank16: correct DPS lab lightness scale

fixes #2987
port 1.5

core/internal/dank16/dank16.go

@@ -313,6 +313,7 @@ func EnsureContrastDPSLstar(hexColor, hexBg string, minLc float64, isLightMode b
 	fg := HexToRGB(hexColor)
 	cf := colorful.Color{R: fg.R, G: fg.G, B: fg.B}
 	Lf, af, bf := cf.Lab()
+	Lf *= 100.0
 
 	dir := 1.0
 	if isLightMode {
@@ -341,6 +342,7 @@ func EnsureContrastDPSBidirectional(hexColor, hexBg string, minLc float64, isLig
 	fg := HexToRGB(hexColor)
 	cf := colorful.Color{R: fg.R, G: fg.G, B: fg.B}
 	origL, af, bf := cf.Lab()
+	origL *= 100.0
 
 	var darkerResult, lighterResult string
 	darkerL, lighterL := origL, origL
@@ -420,6 +422,24 @@ func blendHue(base, target, factor float64) float64 {
 	return result
 }
 
+// color8 sits a fixed L* offset from the background so it keeps its dim role
+// regardless of primary brightness (conventional palettes put ANSI bright
+// black ~2-2.5:1 from the background, e.g. catppuccin-mocha #585b70 on #1e1e2e)
+func DeriveDim(bgHex string, hue, sat float64, isLight bool) string {
+	offset := 22.0
+	if isLight {
+		offset = -offset
+	}
+
+	bgL := getLstar(bgHex)
+	targetL := math.Max(0, math.Min(100, bgL+offset))
+
+	tint := HSVToRGB(HSV{H: hue, S: sat, V: 0.5})
+	c := colorful.Color{R: tint.R, G: tint.G, B: tint.B}
+	_, af, bf := c.Lab()
+	return labToHex(targetL, af, bf)
+}
+
 func DeriveContainer(primary string, isLight bool) string {
 	rgb := HexToRGB(primary)
 	hsv := RGBToHSV(rgb)
@@ -500,10 +520,7 @@ func GeneratePalette(primaryColor string, opts PaletteOptions) Palette {
 		gray7V := baseVal * 0.28
 		palette.Color7 = NewColorInfo(ensureContrastAuto(RGBToHex(HSVToRGB(HSV{H: hsv.H, S: gray7S, V: gray7V})), bgColor, normalTextTarget, opts))
 
-		gray8S := baseSat * 0.05
-		gray8V := baseVal * 0.85
-		dimTarget := secondaryTarget * 0.5
-		palette.Color8 = NewColorInfo(ensureContrastBidirectional(RGBToHex(HSVToRGB(HSV{H: hsv.H, S: gray8S, V: gray8V})), bgColor, dimTarget, opts))
+		palette.Color8 = NewColorInfo(DeriveDim(bgColor, hsv.H, baseSat*0.05, true))
 
 		brightRedS := math.Min(baseSat*1.0, 1.0)
 		brightRedV := math.Min(baseVal*1.2, 1.0)
@@ -559,9 +576,7 @@ func GeneratePalette(primaryColor string, opts PaletteOptions) Palette {
 		gray7V := math.Min(baseVal*1.05, 1.0)
 		palette.Color7 = NewColorInfo(ensureContrastAuto(RGBToHex(HSVToRGB(HSV{H: hsv.H, S: gray7S, V: gray7V})), bgColor, normalTextTarget, opts))
 
-		gray8S := baseSat * 0.15
-		gray8V := baseVal * 0.65
-		palette.Color8 = NewColorInfo(ensureContrastAuto(RGBToHex(HSVToRGB(HSV{H: hsv.H, S: gray8S, V: gray8V})), bgColor, secondaryTarget, opts))
+		palette.Color8 = NewColorInfo(DeriveDim(bgColor, hsv.H, baseSat*0.15, false))
 
 		brightRedS := math.Min(baseSat*0.75, 1.0)
 		brightRedV := math.Min(baseVal*1.35, 1.0)

core/internal/dank16/dank16_test.go

@@ -679,3 +679,73 @@ func TestContrastAlgorithmComparison(t *testing.T) {
 
 	t.Logf("WCAG and DPS palettes differ in %d/16 colors", differentCount)
 }
+
+func TestEnsureContrastDPSLightModeStaysLight(t *testing.T) {
+	tests := []struct {
+		name     string
+		result   string
+		bg       string
+		minLstar float64
+	}{
+		{
+			name:     "bidirectional adjustment",
+			result:   EnsureContrastDPSBidirectional("#d0ccc6", "#f8f8f8", 17.5, true),
+			bg:       "#f8f8f8",
+			minLstar: 20.0,
+		},
+		{
+			name:     "lstar adjustment",
+			result:   EnsureContrastDPSLstar("#c0c0c0", "#f8f8f8", 30.0, true),
+			bg:       "#f8f8f8",
+			minLstar: 20.0,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			lstar := getLstar(tt.result)
+			if lstar < tt.minLstar {
+				t.Errorf("result %s has L* %.2f on light bg %s, expected >= %.2f (collapsed to near-black)",
+					tt.result, lstar, tt.bg, tt.minLstar)
+			}
+		})
+	}
+}
+
+func TestGeneratePaletteColor8Dim(t *testing.T) {
+	hues := []string{"#e91e63", "#f59e0b", "#22c55e", "#06b6d4", "#8b5cf6", "#ef4444"}
+
+	for _, base := range hues {
+		t.Run(base, func(t *testing.T) {
+			palette := GeneratePalette(base, PaletteOptions{IsLight: false, UseDPS: true})
+
+			bgRatio := ContrastRatio(palette.Color8.Hex, palette.Color0.Hex)
+			if bgRatio < 1.5 || bgRatio > 3.0 {
+				t.Errorf("Color8 %s vs bg %s ratio %.2f, expected 1.5-3.0 (bright black stays near bg)",
+					palette.Color8.Hex, palette.Color0.Hex, bgRatio)
+			}
+
+			sepRatio := ContrastRatio(palette.Color4.Hex, palette.Color8.Hex)
+			if sepRatio < 2.0 {
+				t.Errorf("Color4 %s vs Color8 %s ratio %.2f, expected >= 2.0 (blue must not collide with bright black)",
+					palette.Color4.Hex, palette.Color8.Hex, sepRatio)
+			}
+		})
+	}
+}
+
+func TestGeneratePaletteLightColor8StaysLight(t *testing.T) {
+	palette := GeneratePalette("#f59e0b", PaletteOptions{IsLight: true, UseDPS: true})
+
+	lstar := getLstar(palette.Color8.Hex)
+	if lstar < 60.0 {
+		t.Errorf("light mode Color8 %s has L* %.2f, expected >= 60 (dim grey, not near-black)",
+			palette.Color8.Hex, lstar)
+	}
+
+	bgRatio := ContrastRatio(palette.Color8.Hex, palette.Color0.Hex)
+	if bgRatio > 3.0 {
+		t.Errorf("light mode Color8 %s vs bg %s ratio %.2f, expected <= 3.0",
+			palette.Color8.Hex, palette.Color0.Hex, bgRatio)
+	}
+}