Build itself failed.

preConfigure = ''
  dotnet --version > DotnetCliVersion.txt
  for rid in $dotnetRuntimeIds; do dotnet restore --runtime "$rid" "build/_build.csproj"; done
'';
preBuild = ''
  patchShebangs --build build.sh
  ./build.sh Codegen --configuration ${buildType}
'';

...
Executing dotnetBuildHook
patching script interpreter paths in build.sh
build.sh: interpreter directive changed from "#!/usr/bin/env bash" to "/nix/store/q7sqwn7i6w2b67adw0bmix29pxg85x3w-bash-5.3p3/bin/bash"
GNU bash, version 5.3.3(1)-release (x86_64-pc-linux-gnu)
Microsoft (R) .NET Core SDK version 9.0.305
You must install or update .NET to run this application.

App: /build/source/build/bin/Debug/_build
Architecture: x64
Framework: 'Microsoft.NETCore.App', version '8.0.0' (x64)
.NET location: /nix/store/pkvy24cwwrsg3q3rqkhak8k6j98ns5gy-dotnet-sdk-9.0.305/share/dotnet

The following frameworks were found:
  9.0.9 at [/nix/store/pkvy24cwwrsg3q3rqkhak8k6j98ns5gy-dotnet-sdk-9.0.305/share/dotnet/shared/Microsoft.NETCore.App]

Learn more:
https://aka.ms/dotnet/app-launch-failed

To install missing framework, download:
https://aka.ms/dotnet-core-applaunch?framework=Microsoft.NETCore.App&framework_version=8.0.0&arch=x64&rid=linux-x64&os=linux

[whovian@nixos-wsl:/tmp/wat/nix/hactoolnet/source]$ runPhase buildPhase
Running phase: buildPhase
Executing dotnetBuildHook
...
/nix/store/pkvy24cwwrsg3q3rqkhak8k6j98ns5gy-dotnet-sdk-9.0.305/share/dotnet/sdk/9.0.305/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(266,5): error NETSDK1005: Assets file '/tmp/wat/nix/hactoolnet/source/src/hactoolnet/obj/project.assets.json' doesn't have a target for 'net9.0'. Ensure that restore has run and that you have included 'net9.0' in the TargetFrameworks for your project. [/tmp/wat/nix/hactoolnet/source/src/hactoolnet/hactoolnet.csproj]
    0 Warning(s)
    1 Error(s)
...

So it definitely isn't expecting net8 at all, great. Guess I'm looking deeper! 😅

Yeah it seems to be setting TargetFramework to net8.0 in build/_build.csproj so I'll need to patch that and possibly update Nuke.Common in the same csproj

<PackageReference Include="Nuke.Common" Version="8.0.0" />

Good news is that Nuke ran, but throws...

...
Building stage 2 codegen project.
23:53:31 [ERR] Target Codegen has thrown an exception
System.PlatformNotSupportedException: BinaryFormatter serialization and deserialization have been removed. See https://aka.ms/binaryformatter for more information.
   at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize(Stream serializationStream, Object graph)
   at Nuke.Common.Tooling.SettingsEntityExtensions.NewInstance[T](T settingsEntity) in /_/source/Nuke.Tooling/SettingsEntity.NewInstance.cs:line 23
   at Nuke.Common.Tools.DotNet.DotNetRunSettingsExtensions.SetProjectFile[T](T toolSettings, String projectFile) in /_/source/Nuke.Common/Tools/DotNet/DotNet.Generated.cs:line 5507
   at LibHacBuild.Build.RunCodegenStage2() in /tmp/wat/nix/hactoolnet/source/build/Build.cs:line 658
   at LibHacBuild.Build.<get_Codegen>b__70_1() in /tmp/wat/nix/hactoolnet/source/build/Build.cs:line 206
   at Nuke.Common.Execution.BuildExecutor.<>c.<Execute>b__4_2(Action x) in /_/source/Nuke.Build/Execution/BuildExecutor.cs:line 119
   at System.Collections.Generic.List`1.ForEach(Action`1 action)
   at Nuke.Common.Execution.BuildExecutor.Execute(NukeBuild build, ExecutableTarget target, IReadOnlyCollection`1 previouslyExecutedTargets, Boolean failureMode) in /_/source/Nuke.Build/Execution/BuildExecutor.cs:line 119
...

Good news is that Nuke ran, but throws...

...
Building stage 2 codegen project.
23:53:31 [ERR] Target Codegen has thrown an exception
System.PlatformNotSupportedException: BinaryFormatter serialization and deserialization have been removed. See https://aka.ms/binaryformatter for more information.
   at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize(Stream serializationStream, Object graph)
   at Nuke.Common.Tooling.SettingsEntityExtensions.NewInstance[T](T settingsEntity) in /_/source/Nuke.Tooling/SettingsEntity.NewInstance.cs:line 23
   at Nuke.Common.Tools.DotNet.DotNetRunSettingsExtensions.SetProjectFile[T](T toolSettings, String projectFile) in /_/source/Nuke.Common/Tools/DotNet/DotNet.Generated.cs:line 5507
   at LibHacBuild.Build.RunCodegenStage2() in /tmp/wat/nix/hactoolnet/source/build/Build.cs:line 658
   at LibHacBuild.Build.<get_Codegen>b__70_1() in /tmp/wat/nix/hactoolnet/source/build/Build.cs:line 206
   at Nuke.Common.Execution.BuildExecutor.<>c.<Execute>b__4_2(Action x) in /_/source/Nuke.Build/Execution/BuildExecutor.cs:line 119
   at System.Collections.Generic.List`1.ForEach(Action`1 action)
   at Nuke.Common.Execution.BuildExecutor.Execute(NukeBuild build, ExecutableTarget target, IReadOnlyCollection`1 previouslyExecutedTargets, Boolean failureMode) in /_/source/Nuke.Build/Execution/BuildExecutor.cs:line 119
...
/nix/store/pkvy24cwwrsg3q3rqkhak8k6j98ns5gy-dotnet-sdk-9.0.305/share/dotnet/sdk/9.0.305/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(266,5): error NETSDK1005: Assets file '/tmp/wat/nix/hactoolnet/source/src/hactoolnet/obj/project.assets.json' doesn't have a target for 'net9.0'. Ensure that restore has run and that you have included 'net9.0' in the TargetFrameworks for your project. [/tmp/wat/nix/hactoolnet/source/src/hactoolnet/hactoolnet.csproj]
    0 Warning(s)
    1 Error(s)
...

Either way, I was playing whack-a-mole with Nuke 9.0.x, so I wasn't having any luck with my plan either.

... warning NU1603: Nuke.ProjectModel 9.0.3 depends on Microsoft.Build (>= 17.11.4) but Microsoft.Build 17.11.4 was not found. Microsoft.Build 17.12.6 was resolved instead.
... warning NU1701: Package 'Microsoft.Build 17.12.6' was restored using '.NETFramework,Version=v4.6.1, .NETFramework,Version=v4.6.2, .NETFramework,Version=v4.7, .NETFramework,Version=v4.7.1, .NETFramework,Version=v4.7.2, .NETFramework,Version=v4.8, .NETFramework,Version=v4.8.1' instead of the project target framework 'net8.0'. This package may not be fully compatible with your project.