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+# Pure-Nix Material You colorscheme generator: produces the { colors =
+# { dark; light; }; } shape the colorscheme module consumes, assembled from the
+# MD3 role layer (lib/scheme.nix) plus harmonized custom colors. This is our own
+# implementation of the Material You color science (see lib/{math,hct,palettes,
+# scheme}.nix); it replaced the matugen import-from-derivation entirely.
+#
+# Validated against matugen 2.4.1 (material-colors 0.4.2) for #2B3975: all 49 MD3
+# roles are bit-exact in both modes; the 7 custom colors are bit-exact except a
+# few channels that land ±1 LSB off, due to Nix series math vs Rust hardware
+# transcendentals accumulating through the extra harmonize hue rotation.
+{lib}: let
+  h = import ./hct.nix {inherit lib;};
+  p = import ./palettes.nix {inherit lib;};
+  sch = import ./scheme.nix {inherit lib;};
+  m = import ./math.nix {inherit lib;};
+
+  sanitize = d: let r = m.fmod d 360.0; in
+    if r < 0.0
+    then r + 360.0
+    else r;
+  diffDeg = a: b: 180.0 - m.abs (m.abs (a - b) - 180.0);
+  rotDir = a: b:
+    if (sanitize (b - a)) <= 180.0
+    then 1.0
+    else -1.0;
+
+  # Blend.harmonize: shift `custom` hue up to 15 deg toward `source`.
+  harmonizeHue = custHex: srcHex: let
+    f = h.hctFromHex custHex;
+    t = h.hctFromHex srcHex;
+    rot = (let d = diffDeg f.hue t.hue; x = d * 0.5; in
+      if x < 15.0
+      then x
+      else 15.0) * (rotDir f.hue t.hue);
+  in
+    sanitize (f.hue + rot);
+
+  # matugen CustomColorGroup: harmonized-hue tonal palette at chroma 48, with the
+  # same tone map as the primary role set (dark 80/20/30/90, light 40/100/90/10).
+  customGroup = name: custHex: srcHex: let
+    pal = p.tonalPalette (harmonizeHue custHex srcHex) 48.0;
+  in {
+    dark = {
+      "${name}" = pal.tone 80;
+      "on_${name}" = pal.tone 20;
+      "${name}_container" = pal.tone 30;
+      "on_${name}_container" = pal.tone 90;
+      "${name}_source" = lib.toLower custHex;
+      "${name}_value" = lib.toLower custHex;
+    };
+    light = {
+      "${name}" = pal.tone 40;
+      "on_${name}" = pal.tone 100;
+      "${name}_container" = pal.tone 90;
+      "on_${name}_container" = pal.tone 10;
+      "${name}_source" = lib.toLower custHex;
+      "${name}_value" = lib.toLower custHex;
+    };
+  };
+in rec {
+  inherit harmonizeHue customGroup;
+
+  # source: "#rrggbb" (hex). customColors: { name = "#hex"; ... } (blend/harmonized).
+  # Returns { colors = { dark = {..}; light = {..}; }; } matching matugen -j hex.
+  generateColorscheme = source: customColors: let
+    roleColors = isDark: sch.colorsFor isDark source;
+    customFor = isDark: let mode = if isDark then "dark" else "light"; in
+      lib.foldlAttrs (acc: name: hex: acc // (customGroup name hex source).${mode}) {} customColors;
+    modeColors = isDark:
+      (roleColors isDark)
+      // (customFor isDark)
+      // {source_color = lib.toLower source;};
+  in {
+    colors = {
+      dark = modeColors true;
+      light = modeColors false;
+    };
+  };
+}