How can I get my nix package to build using the method defined in `oneTarget`

Question

I have an example repo demonstrating the problem. From the repo's README.md

Need help making packages

The problem I'm having is making packages the way I would like.

In horizon-platoform-template/default.nix compare buildExe with oneTarget

When using buildExe I get the result I want, but not by using native nix, which is what I am trying to do with oneTarget

when using oneTarget this is what happens:

nix build .#example
error:
       … in the left operand of the update (//) operator
         at /nix/store/0d3h8gi2q46fb4l563h6pginjw2a90r4-source/pkgs/development/haskell-modules/lib/compose.nix:48:5:
           47|     ))
           48|     // {
             |     ^
           49|       overrideScope = scope: overrideCabal f (drv.overrideScope scope);

       … while calling a functor (an attribute set with a '__functor' attribute)
         at /nix/store/0d3h8gi2q46fb4l563h6pginjw2a90r4-source/pkgs/development/haskell-modules/lib/compose.nix:41:6:
           40|     f: drv:
           41|     (drv.override (
             |      ^
           42|       args:

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: function 'anonymous lambda' called with unexpected argument 'disallowGhcReference'
       at /nix/store/m9s94alic7s2r6v47p7lwfj58ibc076a-source/pkgs/development/haskell-modules/generic-builder.nix:13:1:
           12|
           13| { pname
             | ^
           14| # Note that ghc.isGhcjs != stdenv.hostPlatform.isGhcjs.

I'm not sure what to do about disallowGhcReference. Also, I'm trying to develop nix troubleshooting skills, so showing methods of troubleshooting this type of problem is valued over getting a succinct solution.

Edit: This latest commit let's me build each step of oneTarget successfully, yet it still fails on the command line

nix repl
flake = builtins.getFlake (toString ./.)
system = "x86_64-linux"
legacyPkgs = flake.outputs.legacyPackages.${system}
hlib = (import <nixpkgs> {}).haskell.lib
lib = (import <nixpkgs> {}).lib
server = legacyPkgs.server
targetName = "exe:horizon-platform-template"
step1 = hlib.setBuildTarget server targetName
:b step1
step2 = hlib.dontCheck step1
:b step2
step3 = hlib.justStaticExecutables step2
:b step3
finalStep = if lib.hasPrefix "exe:" targetName then
  step3.overrideAttrs (old: {
    meta = (old.meta or {}) // { mainProgram = lib.removePrefix "exe:" targetName; };
  })
else
  step3
:b finalStep