[Server] Add getRegistry() method to Server class for debugging access

[camilleislasse]

Summary

Expose the Registry through the Server class to enable debugging and monitoring tools like Symfony Web Profiler to access discovered capabilities.

Changes

• Add ReferenceProviderInterface $registry parameter to Server constructor
• Add getRegistry(): ReferenceProviderInterface method to Server class
• Update ServerBuilder to pass registry to Server constructor
• Update standalone example to use new Server constructor signature
• Add test coverage for getRegistry() method

Use Case

This enables integration with debugging tools like Symfony Web Profiler by providing access to:

• getTools() - All registered tools
• getResources() - All registered resources
• getPrompts() - All registered prompts
• getResourceTemplates() - All registered resource templates

Test Plan

• All existing tests pass
• New test added for getRegistry() method
• PHP CS Fixer validation passes
• PHPStan static analysis passes
• Manual testing with various MCP capabilities confirmed working

Resolves #74

[chr-hertel]

If we make services injectable, it shouldn't be needed to use getters for them since the runtime (or in your case the Symfony DIC) should know them already. Having getters for service dependencies on services leads to misusage for using them to access that service instead of having the explicit dependency. and if the use case is only the profiler toolbar, i'm against adding it. if it is too hard to get the registry instance in a different way, we usually use Traceable* decorator to gather insights for the profiler.

[soyuka]

This makes quite hard to reuse the code of the registry (in #108 I'd like to use my own registry but probably that #108 need a proper fix instead of trying to hack around it). Can we have a setter maybe?

[soyuka]

My PR was @camilleislasse could you check if #111 helps with your use case? We may close this then.

[camilleislasse]

Thanks for the feedback @soyuka and @chr-hertel!

I checked #111 and I see it adds addLoaders(), but I'm not sure how to use it properly for my use case.

@chr-hertel I understand the concerns about getters and using Traceable decorators instead. However, I'm struggling to see how to apply that pattern here since the Registry seems to only exist inside Builder::build() as a local variable and isn't passed to the Server.

Looking at the code after #111, I could technically create a custom Loader that captures the Registry reference when load() is called, but that feels wrong - like I'd be misusing the Loader mechanism just to get access to something.

I might be missing something obvious though. What's the recommended way to access the Registry for profiling purposes? Should I:

1. Create a custom "capture" loader (feels hacky to me)
2. Use a different approach I'm not seeing?
3. Is there a plan to expose the Registry in a future update?

[soyuka]

Loaders give you the ability to fill the registry, I'm not sure why you need access to the Registry? Could you expose exactly what you try to do?