Keep externally set ServiceProvider when ConfigureGlobalOptions triggers a rebuild

[cytoph]

Fixes #251

Problem

When combining the hosting integration with global options, DI breaks silently:

HostApplicationBuilder builder = Host.CreateApplicationBuilder(args);
builder.Services.AddSingleton<Greeter>();
ConsoleApp.ConsoleAppBuilder app = builder.ToConsoleAppBuilder();
app.ConfigureGlobalOptions((ref b) => b.AddGlobalOption<bool>("--verbose"));
app.Add<HelloCommand>();
await app.RunAsync(args);

ConfigureGlobalOptions sets isRequireCallBuildAndSetServiceProvider = true, so the generated BuildAndSetServiceProvider runs during RunAsync, builds an empty ServiceCollection (nothing was configured on the builder itself - the services live in the host), and replaces the ServiceProvider that ToConsoleAppBuilder had already set. Constructor dependencies then resolve to null and blow up with NullReferenceException on first use.

Fix

The generated BuildAndSetServiceProvider now returns early when ConsoleApp.ServiceProvider is already set and nothing DI-related was configured on the builder itself (configureServices, createServiceProvider, postConfigureServices, and configureLogging where applicable, all null). The flag-set in ConfigureGlobalOptions is left untouched, because the flag also gates global-options parsing in the generated Run path for context-less commands.

Generated code (with DependencyInjection referenced) now begins:

partial void BuildAndSetServiceProvider(ConsoleAppContext context)
{
    if (!isRequireCallBuildAndSetServiceProvider)
    {
        return;
    }
    isRequireCallBuildAndSetServiceProvider = false;

    if (ConsoleApp.ServiceProvider != null && configureServices == null && createServiceProvider == null && postConfigureServices == null)
    {
        return;
    }
    ...

Behavior when a provider was configured on the builder (or none was set externally) is unchanged.

Test

DITest.ConfigureGlobalOptionsKeepsExternallySetServiceProvider reproduces the issue with a pre-set ServiceProvider plus ConfigureGlobalOptions and asserts that the service still resolves and the global option is still parsed. It fails without the fix and passes with it.

Since the DI emit path (DllReference.HasDependencyInjection) had no coverage in GeneratorTests, the runner gained an optional additionalReferences parameter and the test project references Microsoft.Extensions.DependencyInjection 8.0.1 (8.x on purpose: its net8.0 lib matches the runner's .NET 8 reference assemblies; 9.x triggers CS1705).

🤖 Generated with Claude Code