diff --git a/.pi/prompts/review.md b/.pi/prompts/review.md
index e115e3f..d732bbd 100644
--- a/.pi/prompts/review.md
+++ b/.pi/prompts/review.md
@@ -17,6 +17,15 @@ If the target includes multiple matching file types, use all matching skills.
 If the target is a diff, choose skills from the changed files.
 Do not use a style skill when no reviewed file matches it.
 
+For every reviewed `*.nix` file, run:
+
+```bash
+bazel run //src/natu:natu -- <reviewed-nix-paths>
+```
+
+Pass every reviewed Nix path to Natu.
+Report every Natu diagnostic as an actionable finding.
+
 Report only actionable findings.
 Order findings by severity.
 Do not report preferences unless a loaded rule states them.
@@ -36,6 +45,7 @@ Keep the code excerpt to one to three lines when possible.
 Use a longer excerpt only when the violation needs surrounding context.
 Use `...` to omit unrelated lines from a multi-line excerpt.
 Use a style-skill rule citation in the form `skill::rule-file:line`.
+Cite Natu diagnostics as `natu::<rule-id>`.
 Make the fix direct.
 Do not include alternatives when one fix best follows the cited rule.
 
diff --git a/src/dotfiles/default.nix b/src/dotfiles/default.nix
index 245364c..2a53e2a 100644
--- a/src/dotfiles/default.nix
+++ b/src/dotfiles/default.nix
@@ -17,7 +17,7 @@ let
   util = import ./util.nix { inherit lib; };
 
   registry = import ./registry.nix {
-    inherit lib;
+    inherit lib util;
     hosts = self.nixosConfigurations;
     root = root + "/registry";
   };
diff --git a/src/dotfiles/guests.nix b/src/dotfiles/guests.nix
index ba4cad9..896ff97 100644
--- a/src/dotfiles/guests.nix
+++ b/src/dotfiles/guests.nix
@@ -276,10 +276,7 @@ let
       };
     };
 
-  names = map (file: lib.removeSuffix ".nix" file) (lib.attrNames guestFiles);
-  guestFiles = lib.filterAttrs (file: type: type == "regular" && lib.hasSuffix ".nix" file) (
-    builtins.readDir root
-  );
+  names = map (path: lib.removeSuffix ".nix" (builtins.baseNameOf path)) files;
 in
 {
   imports = files ++ map mkGuest names;
diff --git a/src/dotfiles/registry.nix b/src/dotfiles/registry.nix
index 8d6c2e0..6950765 100644
--- a/src/dotfiles/registry.nix
+++ b/src/dotfiles/registry.nix
@@ -2,20 +2,14 @@
   hosts,
   lib,
   root,
+  util,
 }:
 let
-  definitions =
-    lib.mapAttrs'
-      (
-        name: _type:
-        let
-          path = root + "/${name}";
-        in
-        lib.nameValuePair (registryName name) (mkRegistry path)
-      )
-      (
-        lib.filterAttrs (name: type: type == "regular" && lib.hasSuffix ".nix" name) (builtins.readDir root)
-      );
+  definitions = lib.listToAttrs (
+    map (path: lib.nameValuePair (registryName (builtins.baseNameOf path)) (mkRegistry path)) (
+      util.collectNixFiles root
+    )
+  );
 
   registryName = fileName: lib.removeSuffix ".nix" fileName;
 
diff --git a/src/skills/style/nix/rules/general.md b/src/skills/style/nix/rules/general.md
new file mode 100644
index 0000000..3b51109
--- /dev/null
+++ b/src/skills/style/nix/rules/general.md
@@ -0,0 +1,12 @@
+## Discover Nix files
+
+### Rule
+
+Use `util.collectNixFiles` to discover Nix files.
+Do not use `builtins.readDir` with a `.nix` suffix filter for this purpose.
+Pass `util` to Nix functions that need the helper.
+
+### Rationale
+
+`util.collectNixFiles` centralizes recursive discovery of Nix files.
+Repository Nix code uses one implementation.