diff --git a/nixos/hosts/phantom-ship.nix b/nixos/hosts/phantom-ship.nix
index d91e229..ec3a6b5 100644
--- a/nixos/hosts/phantom-ship.nix
+++ b/nixos/hosts/phantom-ship.nix
@@ -583,12 +583,37 @@ in
 
   # Catppuccin theme for Forgejo — module wired in via clan.nix's
   # phantom-ship.imports (inputs.catppuccin.nixosModules.catppuccin).
+  # The module's `flavor` option picks ONE static flavor; the auto
+  # variants (catppuccin-<accent>-auto) follow prefers-color-scheme —
+  # latte in light mode, mocha in dark. We override DEFAULT_THEME +
+  # THEMES below to use the auto variant.
   catppuccin.forgejo = {
     enable = true;
-    flavor = "mocha";
+    flavor = "mocha";        # static fallback; auto-variant takes precedence below
     accent = "mauve";
   };
 
+  # Default to the auto-switching mauve theme (light in light mode, dark
+  # in dark mode). Replace THEMES with builtins + every catppuccin auto
+  # variant + the four mauve flavor variants, so the user-level
+  # appearance picker can still offer them.
+  services.forgejo.settings.ui = {
+    DEFAULT_THEME = lib.mkForce "catppuccin-mauve-auto";
+    THEMES = lib.mkForce (lib.concatStringsSep "," [
+      # Forgejo builtins
+      "forgejo-auto" "forgejo-light" "forgejo-dark"
+      # Auto-switching catppuccin (light in light mode, dark in dark mode)
+      "catppuccin-blue-auto" "catppuccin-flamingo-auto" "catppuccin-green-auto"
+      "catppuccin-lavender-auto" "catppuccin-maroon-auto" "catppuccin-mauve-auto"
+      "catppuccin-peach-auto" "catppuccin-pink-auto" "catppuccin-red-auto"
+      "catppuccin-rosewater-auto" "catppuccin-sapphire-auto" "catppuccin-sky-auto"
+      "catppuccin-teal-auto" "catppuccin-yellow-auto"
+      # Static mauve variants for manual override
+      "catppuccin-latte-mauve" "catppuccin-frappe-mauve"
+      "catppuccin-macchiato-mauve" "catppuccin-mocha-mauve"
+    ]);
+  };
+
   # Auto-rebuild service/timer + safe.directory provided by the
   # shared dotfiles-rebuild NixOS module (see nixos/modules/dotfiles-rebuild.nix).
 }