Expand a few DI-related tests

[stephentoub]

No description provided.

[halter73]

Suggested change

	IServiceProvider services = sc.BuildServiceProvider();
	McpServerTool tool = services.GetRequiredService<McpServerTool>();
	IServiceProvider services = sc.BuildServiceProvider(validateScopes: true);
	await using var scope = services.CreateAsyncScope();
	McpServerTool tool = scope.ServiceProvider.GetRequiredService<McpServerTool>();

Nit: Not a big deal since this is just a test, but resolving a scoped service without first creating a scope is bad practice, and our hosts now guard against it in dev environments. https://learn.microsoft.com/en-us/dotnet/core/compatibility/aspnet-core/9.0/hostbuilder-validation

Again, it doesn't really matter, but it's good to always show resolving scoped services from a scope. We might need to update SetupGet(x => x.Services).Returns(scope.ServiceProvider); below.

[halter73]

I didn't see you had already merged. Nevermind. It's definitely no big deal.

[stephentoub]

resolving a scoped service without first creating a scope is bad practice

Is there a product change we need here, to ensure the IServiceProvider passed to the tool's invocation is appropriately scoped? I'm looking at #198 wondering how to repro that, but maybe we need to be creating a scope as part of a stdio server's handling?

[halter73]

I don't think we need to make any product changes related to scopes. At least not without deeper discussion.

Using scoped services in MCP tools is not currently supported for stdio scenarios (unless you disable validation) because there are no scopes. Without creating scopes, it's hard to see the point of scoped services anyway. You should be able to resolve request scoped services in tools invoked via MapMcp though. I'll add tests for this in my next PR.

[stephentoub]

unless you disable validation

Where is that validation coming from / why is my test above not hitting it?

[halter73]

The validation is coming from the host in "development" environments from here. This used to always default to false until .NET 9.

I also left a comment on #198 after making my last comment here. After further thought, I do think we should make product changes. We should create a scope per handler invocation. I assigned the issue to myself.

[stephentoub]

The validation is coming from the host in "development" environments from here. This used to always default to false until .NET 9.

Ok, so this test isn't hitting that because it's not using a host.