IncrementalGenerator Generated Source Not Available

Following this answer I'm trying to reimplement my ISourceGenerator as an IIncrementalGenerator following along with these docs.

Now, I've got my main initializer method here:

	public void Initialize(IncrementalGeneratorInitializationContext context)
	{
		SpinWait.SpinUntil(() => Debugger.IsAttached); // Manually attach debugger here

		IncrementalValuesProvider<AdditionalText> extraTexts = context.AdditionalTextsProvider.Where(f => f.Path.EndsWith(".fluid.yml"));
		IncrementalValuesProvider<(string Name, string Content)> namesAndContents = extraTexts.Select((text, cancellationToken)
																										  => (Name: Path.GetFileNameWithoutExtension(text.Path),
																											  Content: text.GetText(cancellationToken)!.ToString()));

		context.RegisterSourceOutput(namesAndContents, (spc, nameAndContent) =>
													   {
														   Dictionary<string, string> generatedSource = _generatorService.Generate(nameAndContent.Content);
														   foreach ((string fileName, string source) in generatedSource)
														   {
															   spc.AddSource(fileName, source);
														   }
													   });
	}

If I drop a breakpoint on the spc.AddSource() line, I can see that the contents of my generatedSource dictionary looks like:

ICanLockOrEnter.fluid.g.cs:

namespace SuperFluid.Tests.Cars;

public interface ICanLockOrEnter
{
	public ICanUnlockOrInitialize Lock();
	public ICanStartOrExit Enter();
}

Which all looks fine to me.

If I add EmitCompilerGeneratedFiles to my .csproj, I can even see that the files are correctly generated within the obj folder.

However, despite this, I can't reference any of these interfaces in my test project that's using the analyzer.

Am I missing a trick here? The analyzer seems to be running, if I debug it, the sources look fine, so why can't I reference them?

This seems to be an IDE issue.

Invalidating Rider's caches and restarting solved the problem.