diff --git a/AGENTS.md b/AGENTS.md
index b65775d..fa09456 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -20,6 +20,8 @@ The domain model (Host, Module, Skeleton, Auto-loader, Enable convention, overla
 
 - Subagent completion delivery is non-blocking through immediate spawn, milestone notifications, retained terminal entries, and `subagent_list` or `subagent_result` retrieval.
   `subagent_wait` intentionally blocks the parent tool call until its condition or timeout, so do not use it merely to keep background work alive during an interactive workflow.
+- Nixvim's flake input following the root nixpkgs source does not make its Home Manager module reuse the host's `pkgs` instance.
+  Keep `programs.nixvim.nixpkgs.useGlobalPackages = true` so Nixvim uses the shared package set without warning that its source default was affected.
 - This host has no `python` or `python3` command on its ordinary `PATH`.
   For ad hoc Python, use Nix explicitly, such as `nix shell nixpkgs#python3 -c python3 <script>`.
 - ADR bodies are immutable records of decisions as they were made, while frontmatter is mutable.
diff --git a/flake.nix b/flake.nix
index 410c00a..0cf99e5 100644
--- a/flake.nix
+++ b/flake.nix
@@ -100,7 +100,11 @@
 
       # `nix flake check` builds each host's toplevel.
       checks.x86_64-linux = lib.mapAttrs (
-        _name: host: host.config.system.build.toplevel
+        name: host:
+        if host.config.warnings == [] then
+          host.config.system.build.toplevel
+        else
+          throw "Host ${name} has evaluation warnings:\n${lib.concatStringsSep "\n" host.config.warnings}"
       ) self.nixosConfigurations;
     };
 }
diff --git a/modules/desktop/theming.nix b/modules/desktop/theming.nix
index 730edba..ea03729 100644
--- a/modules/desktop/theming.nix
+++ b/modules/desktop/theming.nix
@@ -32,6 +32,9 @@ in
 
       image = wallpaper;
 
+      # Regreet is not enabled, so its styling target stays off.
+      targets.regreet.enable = false;
+
       cursor = {
         package = pkgs.bibata-cursors;
         # Solid white with a dark outline, so it stays easy to spot against the
diff --git a/modules/nvim/nvim.nix b/modules/nvim/nvim.nix
index 6649ad9..3272356 100644
--- a/modules/nvim/nvim.nix
+++ b/modules/nvim/nvim.nix
@@ -19,6 +19,7 @@ in
     home-manager.users.${user} = hm: {
       programs.nixvim = {
         enable = true;
+        nixpkgs.useGlobalPackages = true;
 
         extraPackages = with pkgs; [
           git # neogit and gitsigns shell out to git