Decision Matrix

Use this matrix to quickly choose the right contract and dispatch call.

Message Type Matrix

You Need	Define Contract As	Implement Handler	Call	Handler Count
One response value	IRequest<TResponse>	IRequestHandler<TRequest, TResponse>	Send(...)	Exactly one
No response value	IRequest	IRequestHandler<TRequest>	Send(...)	Exactly one
Fan-out event	INotification	INotificationHandler<TNotification>	Publish(...)	Zero to many
Async stream of values	IStreamRequest<TResponse>	IStreamRequestHandler<TRequest, TResponse>	CreateStream(...)	Exactly one

Cross-Cutting Matrix

Concern	Extension Point	Applies To	Can Short-Circuit
Validation before handling	IRequestPreProcessor<TRequest>	Requests and streams (IBaseRequest)	No
Around request execution	IPipelineBehavior<TRequest, TResponse>	Request/response and void requests	Yes
Around stream execution	IStreamPipelineBehavior<TRequest, TResponse>	Stream requests	Yes
Post-handle side effects	IRequestPostProcessor<TRequest, TResponse>	Request/response and void requests	No
Recover from known exceptions	IRequestExceptionHandler<TRequest, TResponse, TException>	Request/response and void requests	Yes (SetHandled)
Side effects on unhandled exceptions	IRequestExceptionAction<TRequest, TException>	Request/response and void requests	No
Recover from stream exceptions	IStreamRequestExceptionHandler<TRequest, TResponse, TException>	Stream requests	Yes (SetHandled)

Notification Delivery Matrix

Strategy	Configure	Best For	Tradeoff
Sequential	UseNotificationPublisherStrategy(Sequential)	Deterministic order and simpler tracing	Lower throughput
Parallel	UseNotificationPublisherStrategy(Parallel)	Faster fan-out when handlers are independent	Concurrency and aggregate exception handling

Package Selection Matrix

Project Type	Package
Contracts-only shared library	Nerdigy.Mediator.Contracts
Application runtime without DI helper	Nerdigy.Mediator + Nerdigy.Mediator.Contracts
Typical app with IServiceCollection	Nerdigy.Mediator.DependencyInjection (transitively includes runtime + contracts)

LLM Prompt Helper

Use this decision stub in prompts:

Pick mediator contract using these rules:
- If exactly one response is needed: IRequest<TResponse> + Send
- If no response is needed: IRequest + Send
- If one-to-many event fan-out is needed: INotification + Publish
- If progressive results are needed: IStreamRequest<TResponse> + CreateStream

Registration Quick Reference

services.AddMediator(options =>
{
    options.RegisterServicesFromAssemblyContaining<Program>();
    options.UseNotificationPublisherStrategy(
        NerdigyMediatorNotificationPublisherStrategy.Sequential);
    options.AddOpenBehavior(typeof(LoggingBehavior<,>));
});