feat: add flake develop zsh hook

users/gandalf/modules/zsh.nix

@@ -1,4 +1,4 @@
-{ config, ... }: {
+{ config, pkgs, ... }: {
   programs.zsh = {
     enable = true;
     enableCompletion = true;
@@ -12,10 +12,26 @@
         "git"
       ];
     };
+
     history = {
       path = "${config.xdg.dataHome}/zsh/histfile";
       size = 10000;
       save = 10000;
     };
+
+    initExtra = ''
+      nix_dev_env() {
+        FLAKE="$PWD/flake.nix"
+        [[ -z "$CURRENT_FLAKE_ENV" ]]          && \
+        [[ -f $FLAKE ]]                        && \
+          ZSH_PREFIX="$ZSH_PREFIX(flake)"         \
+          CURRENT_FLAKE_ENV=$FLAKE                \
+          nix develop -c $SHELL 2> /dev/null
+      }
+      autoload -U add-zsh-hook
+      add-zsh-hook chpwd nix_dev_env
+
+      export PS1="$ZSH_PREFIX$PS1"
+    '';
   };
 }