refactor: split n8n overlay override

tests/n8n-overlay-test.nix

@@ -4,15 +4,16 @@
   self,
 }: let
   localPackages = import ../pkgs {inherit pkgs inputs;};
-  mkPkgsWithOverlay = overlay:
+  mkPkgs = overlays:
     import inputs.nixpkgs {
       system = pkgs.stdenv.hostPlatform.system;
       config.allowUnfree = true;
-      overlays = [overlay];
+      inherit overlays;
     };
 
-  modifiedPkgs = mkPkgsWithOverlay self.overlays.modifications;
-  defaultPkgs = mkPkgsWithOverlay self.overlays.default;
+  upstreamPkgs = mkPkgs [];
+  modifiedPkgs = mkPkgs [self.overlays.modifications];
+  defaultPkgs = mkPkgs [self.overlays.default];
 
   expectedVersion = "2.29.4";
   expectedSrcHash = "sha256-Vc10fXKn21PSlv6Sk+5zyi2efkKup1Vi+9+vyJd2I1k=";
@@ -29,14 +30,27 @@
     else if package.meta.changelog != expectedChangelog
     then throw "${overlayName} n8n changelog is ${package.meta.changelog}, expected ${expectedChangelog}"
     else "ok";
+
+  checkPhasesInherited = overlayName: package:
+    if (package.preBuild or null) != (upstreamPkgs.n8n.preBuild or null)
+    then throw "${overlayName} n8n preBuild should be inherited from upstream nixpkgs"
+    else if package.buildPhase != upstreamPkgs.n8n.buildPhase
+    then throw "${overlayName} n8n buildPhase should be inherited from upstream nixpkgs"
+    else "ok";
 in
   pkgs.runCommand "n8n-overlay-test" {
+    n8nOverlayFile =
+      if builtins.pathExists ../overlays/mods/n8n.nix
+      then "ok"
+      else throw "n8n overlay override must live in overlays/mods/n8n.nix";
     localN8nAbsent =
       if localPackages ? n8n
       then throw "pkgs/default.nix must not export a local n8n package"
       else "ok";
     modificationsOverlayN8n = checkN8nOverride "overlays.modifications" modifiedPkgs.n8n;
     defaultOverlayN8n = checkN8nOverride "overlays.default" defaultPkgs.n8n;
+    modificationsOverlayPhases = checkPhasesInherited "overlays.modifications" modifiedPkgs.n8n;
+    defaultOverlayPhases = checkPhasesInherited "overlays.default" defaultPkgs.n8n;
   } ''
     touch $out
   ''