feat(macos): Alacritty follows system light/dark appearance

New setup — due for review after you run darwin-rebuild switch and
live with it for a few days. See CLAUDE.md (Alacritty) and
assets/alacritty/README.md.

- HM: import active-colors.toml + Catppuccin latte/mocha fragments
- nix-darwin: launchd.user.agents.alacritty-system-theme + PATH helper
- fish: background sync on Darwin; theme.sh no longer rebuilds for Alacritty
- Remove switch-alacritty-theme.sh (sed + darwin-rebuild per toggle)

Made-with: Cursor

nixos/fish.nix

@@ -24,6 +24,11 @@
 
       set fish_greeting 🐟: (set_color yellow; date +%T; set_color green; date --iso-8601 2>/dev/null; or date +%F; set_color normal)
 
+      # Alacritty palette follows macOS appearance; refresh when opening a shell (LaunchAgent also polls).
+      if test (uname -s) = Darwin
+        bash ~/dotfiles/scripts/alacritty-sync-system-theme.sh >/dev/null 2>&1 &
+      end
+
       # name: Default
       # author: Lily Ballard
       # edits: DannyDannyDanny

nixos/home/danny/home.nix

@@ -1,4 +1,4 @@
-{ pkgs, lib, zen-browser ? null, ... }:
+{ pkgs, lib, config, zen-browser ? null, ... }:
 {
   # TODO: remove next two lines from here or from flake.nix
   # home.username = "danny";
@@ -112,15 +112,26 @@
     executable = true;
   };
 
-  # Alacritty terminal configuration with conditional theme switching
+  # Palette fragments: synced to system appearance (see scripts/alacritty-sync-system-theme.sh).
+  xdg.configFile."alacritty/catppuccin-latte-colors.toml".source =
+    ../../../assets/alacritty/catppuccin-latte-colors.toml;
+  xdg.configFile."alacritty/catppuccin-mocha-colors.toml".source =
+    ../../../assets/alacritty/catppuccin-mocha-colors.toml;
+
+  # Alacritty: base config + imported active-colors.toml (updated without rebuild)
   programs.alacritty = {
     enable = true;
     settings = {
+      general = {
+        live_config_reload = true;
+        import = [ "${config.xdg.configHome}/alacritty/active-colors.toml" ];
+      };
       window = {
         padding = { x = 8; y = 8; };
         dynamic_padding = true;
         decorations = "buttonless";
-        opacity = 0.95;
+        decorations_theme_variant = "None";
+        opacity = 1.0;
         startup_mode = "Maximized";
         option_as_alt = "Both";
       };
@@ -134,43 +145,19 @@
           program = "${pkgs.fish}/bin/fish";
         };
       };
-      # Conditional colors based on system theme
-      colors = let
-        # Set this to true for light theme, false for dark theme
-        # You can change this and run 'darwin-rebuild switch' to switch themes
-        isLightTheme = true;
-
-        # Catppuccin Latte (Light) colors
-        lightColors = {
-          primary = { background = "0xeff1f5"; foreground = "0x4c4f69"; };
-          cursor = { text = "0xeff1f5"; cursor = "0xdc8a78"; };
-          normal = {
-            black = "0x5c5f77"; red = "0xd20f39"; green = "0x40a02b"; yellow = "0xdf8e1d";
-            blue = "0x1e40af"; magenta = "0xea76cb"; cyan = "0x179299"; white = "0xacb0be";
-          };
-          bright = {
-            black = "0x6c6f85"; red = "0xd20f39"; green = "0x40a02b"; yellow = "0xdf8e1d";
-            blue = "0x1e40af"; magenta = "0xea76cb"; cyan = "0x179299"; white = "0xbcc0cc";
-          };
-        };
-
-        # Catppuccin Mocha (Dark) colors
-        darkColors = {
-          primary = { background = "0x1e1e2e"; foreground = "0xcdd6f4"; };
-          cursor = { text = "0x1e1e2e"; cursor = "0xf5e0dc"; };
-          normal = {
-            black = "0x45475a"; red = "0xf38ba8"; green = "0xa6e3a1"; yellow = "0xf9e2af";
-            blue = "0x89b4fa"; magenta = "0xf5c2e7"; cyan = "0x94e2d5"; white = "0xbac2de";
-          };
-          bright = {
-            black = "0x585b70"; red = "0xf38ba8"; green = "0xa6e3a1"; yellow = "0xf9e2af";
-            blue = "0x89b4fa"; magenta = "0xf5c2e7"; cyan = "0x94e2d5"; white = "0xa6adc8";
-          };
-        };
-      in if isLightTheme then lightColors else darkColors;
     };
   };
 
+  # Writable copy (not a symlink to the store — cp in the sync script must replace a real file).
+  home.activation.alacrittySystemTheme = lib.hm.dag.entryAfter [ "writeBoundary" ] ''
+    MOCHA="${config.xdg.configHome}/alacritty/catppuccin-mocha-colors.toml"
+    ACTIVE="${config.xdg.configHome}/alacritty/active-colors.toml"
+    if [ ! -f "$ACTIVE" ]; then
+      $DRY_RUN_CMD cp "$MOCHA" "$ACTIVE"
+    fi
+    $DRY_RUN_CMD ${pkgs.bash}/bin/bash "${../../../scripts/alacritty-sync-system-theme.sh}" || true
+  '';
+
 
   # TODO: Put user-installed binaries here if you want HM to own them (optional)
   # Fonts

nixos/hosts/macos.nix

@@ -1,6 +1,9 @@
 { config, lib, pkgs, ... }:
 
-{
+let
+  alacrittySyncSystemTheme = pkgs.writeShellScriptBin "alacritty-sync-system-theme"
+    (builtins.readFile ../../scripts/alacritty-sync-system-theme.sh);
+in {
   # Apple Silicon + nix-darwin basics
   nixpkgs.hostPlatform = "aarch64-darwin";
   nix.enable = false; # Determinate manages Nix
@@ -48,6 +51,19 @@
   # User-specific packages and environment variables are now in home-manager (home.nix)
   # Only system-level packages should remain here if needed
 
+  environment.systemPackages = [ alacrittySyncSystemTheme ];
+
+  # Poll macOS appearance; updates ~/.config/alacritty/active-colors.toml (Alacritty live_config_reload).
+  launchd.user.agents.alacritty-system-theme = {
+    serviceConfig = {
+      RunAtLoad = true;
+      StartInterval = 30;
+      ProgramArguments = [ "${alacrittySyncSystemTheme}/bin/alacritty-sync-system-theme" ];
+      StandardOutPath = "/tmp/alacritty-theme-sync.log";
+      StandardErrorPath = "/tmp/alacritty-theme-sync-error.log";
+    };
+  };
+
   # Keep for darwin as well (tracks defaults across upgrades)
   # current max per nix-darwin; bump only if a release notes says so
   system.stateVersion = 6;