Add --start flag to codegen command for Startup.Configure() pattern

build/Build.cs

@@ -104,6 +104,7 @@ partial class Build : NukeBuild
             DotNet("run --framework net9.0 -- describe --file description.txt", Solution.TestHarnesses.CommandLineRunner.Directory);
             DotNet("run --framework net9.0 -- describe --environment Testing --applicationName Different --contentRoot /bin", Solution.TestHarnesses.CommandLineRunner.Directory);
             DotNet("run --framework net9.0 -- describe --environment=Testing --applicationName=Different --contentRoot=/bin", Solution.TestHarnesses.CommandLineRunner.Directory);
+            DotNet("run --framework net9.0 -- codegen preview --start", Solution.TestHarnesses.CommandLineRunner.Directory);
         });
 
     AbsolutePath ArtifactsDirectory => RootDirectory / "artifacts";

src/JasperFx/CodeGeneration/Commands/GenerateCodeCommand.cs

@@ -21,9 +21,18 @@ public GenerateCodeCommand()
     public override bool Execute(GenerateCodeInput input)
     {
         DynamicCodeBuilder.WithinCodegenCommand = true;
-        
+
         using var host = input.BuildHost();
 
+        // When using the old ASP.NET Core Startup.Configure() pattern,
+        // code generation participants (like Wolverine.Http endpoints) are
+        // registered during host startup, not during Build(). Starting the
+        // host ensures Configure() runs and all participants are discovered.
+        if (input.StartFlag)
+        {
+            host.StartAsync().GetAwaiter().GetResult();
+        }
+
         var collections = host.Services.GetServices<ICodeFileCollection>().ToArray();
         if (!collections.Any())
         {

src/JasperFx/CodeGeneration/Commands/GenerateCodeInput.cs

@@ -8,4 +8,7 @@ public class GenerateCodeInput : NetCoreInput
 
     [Description("Optionally limit the preview to only one type of code generation")]
     public string? TypeFlag { get; set; }
+
+    [Description("Start the IHost instead of just building it. Use this when code generation participants are registered during host startup (e.g., ASP.NET Core Startup.Configure)")]
+    public bool StartFlag { get; set; }
 }

src/JasperFx/JasperFx.csproj

@@ -3,7 +3,7 @@
         <Description>Foundational helpers and command line support used by JasperFx and the Critter Stack projects</Description>
         <AssemblyName>JasperFx</AssemblyName>
         <PackageId>JasperFx</PackageId>
-        <Version>1.21.5</Version>
+        <Version>1.21.6</Version>
     </PropertyGroup>
 
     <ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">