fix: use the right nixpkgs when consuming overlays

lib/flake/default.nix

@@ -79,15 +79,9 @@ rec {
         overrides = (full-flake-options.modules or { });
       };
       overlays = core-inputs.flake-utils-plus.lib.exportOverlays ({
-        inherit (user-inputs.self) pkgs;
-        inputs = user-inputs;
+        inherit (user-inputs.self) pkgs inputs;
       });
 
-      overlay = (final: prev:
-        snowfall-lib.attrs.merge-deep
-          (builtins.map (overlay: overlay final prev) (builtins.attrValues overlays))
-      );
-
       outputs-builder = channels:
         let
           user-outputs-builder =
@@ -113,7 +107,7 @@ rec {
         snowfall-lib.attrs.merge-deep [ user-outputs outputs ];
 
       flake-options = custom-flake-options // {
-        inherit hosts templates overlays overlay;
+        inherit hosts templates overlays;
         inherit (user-inputs) self;
 
         lib = snowfall-lib.internal.user-lib;
@@ -130,6 +124,16 @@ rec {
 
         outputsBuilder = outputs-builder;
       };
+
+      flake-outputs =
+        core-inputs.flake-utils-plus.lib.mkFlake flake-options;
+
+      overlay = (final: prev:
+        snowfall-lib.attrs.merge-deep
+          (builtins.map (overlay: overlay final prev) (builtins.attrValues flake-outputs.overlays))
+      );
     in
-    core-inputs.flake-utils-plus.lib.mkFlake flake-options;
+    flake-outputs // {
+      inherit overlay;
+    };
 }

lib/overlay/default.nix

@@ -25,6 +25,7 @@ in
         user-packages-overlay = final: prev:
           let
             user-packages = snowfall-lib.package.create-packages {
+              pkgs = prev;
               channels = channels;
             };
             user-packages-without-default = builtins.removeAttrs
@@ -32,6 +33,14 @@ in
           in
           if overlay-package-namespace == null then
             user-packages-without-default
+          else if prev ? "${overlay-package-namespace}" then
+            {
+              ${overlay-package-namespace} =
+                snowfall-lib.attrs.merge-deep [
+                  prev.${overlay-package-namespace}
+                  user-packages-without-default
+                ];
+            }
           else
             {
               ${overlay-package-namespace} = user-packages-without-default;

lib/package/default.nix

@@ -17,13 +17,14 @@ in
     create-packages =
       { channels
       , src ? user-packages-root
+      , pkgs ? channels.nixpkgs
       , overrides ? { }
       }:
       let
         user-packages = snowfall-lib.fs.get-default-nix-files-recursive src;
         create-package-metadata = package: {
           name = builtins.unsafeDiscardStringContext (snowfall-lib.path.get-parent-directory package);
-          drv = channels.nixpkgs.callPackage package {
+          drv = pkgs.callPackage package {
             inherit channels;
             lib = snowfall-lib.internal.system-lib;
           };

lib/system/default.nix

@@ -155,7 +155,6 @@ in
       let
         lib = snowfall-lib.internal.system-lib;
       in
-      # (lib.traceSeqN 1 path)
       {
         inherit channelName system builder output;