.NET: library-first agent registration via IServiceCollection + IEndpointRouteBuilder A2A mapping (#1454)

[jst4upiyush]

feat(hosting,a2a): library-first agent registration + A2A route builder helpers (#1454)

Adds additive, dependency-light APIs:

• IServiceCollection.AddAIAgent overloads (name + instructions + optional chat client / key / description)
• Forwarding IHostApplicationBuilder overloads (compat only)
• IEndpointRouteBuilder.MapA2A overloads (agentName + path, optional AgentCard or preconfigured TaskManager) — no WebApplication requirement

Why:

• Library-first scenarios often only depend on IServiceCollection
• Reduce boilerplate (common case no longer needs factory delegate)
• Enable modular A2A mapping inside grouped endpoints

Backward compatibility:

• No removals or behavior changes; existing factory APIs preserved
• Potential future deprecation path for host builder variants

Testing:

• Full solution builds (Release) & existing unit/integration tests pass locally

Example:

// Library or startup
services.AddAIAgent("support-bot", "You are a helpful assistant.");

services.AddAIAgent(
    name: "pricing",
    instructions: "Answer pricing questions precisely.",
    description: "Handles SKU + tier pricing queries.",
    chatClientServiceKey: "gpt-4o");

// In endpoint config
var a2aGroup = app.MapGroup("/a2a");
a2aGroup.MapA2A("support-bot", "/support");
a2aGroup.MapA2A("pricing", "/pricing", new AgentCard { Name = "Pricing", Description = "Pricing specialist" });

Checklist:

• Add IServiceCollection overloads
• Forward host builder overloads
• Add A2A route builder mapping
• Preserve factory-based APIs
• Build + tests pass

[Copilot]

Pull Request Overview

This PR adds library-first, dependency-light APIs for AI agent registration and A2A endpoint mapping. The changes enable service collection-based agent registration without requiring a full host application builder and allow A2A endpoint mapping on any IEndpointRouteBuilder.

• Adds IServiceCollection.AddAIAgent overloads for direct service collection configuration
• Updates IHostApplicationBuilder methods to forward to the new service collection extensions
• Changes A2A mapping from WebApplication to IEndpointRouteBuilder for more flexible routing scenarios

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
HostApplicationBuilderAgentExtensions.cs	Refactored to delegate to new service collection extensions and removed duplicate validation logic
AgentHostingServiceCollectionExtensions.cs	Added new service collection extension methods for agent registration with various overloads
EndpointRouteBuilderExtensions.cs	Changed A2A mapping from WebApplication to IEndpointRouteBuilder and updated class name
Program.cs	Updated sample to use new service collection-based registration API

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[jst4upiyush]

@microsoft-github-policy-service agree company="ClrSlate"

[DeagleGross]

Thanks for the PR!

[DeagleGross]

I would call it just ServiceCollectionExtensions because of the convention

[DeagleGross]

And we should add tests similar to

agent-framework/dotnet/tests/Microsoft.Agents.AI.Hosting.UnitTests/HostApplicationBuilderAgentExtensionsTests.cs

Line 11 in 731e3a7

public class HostApplicationBuilderAgentExtensionsTests

[DeagleGross]

this (and other AddAIAgent) should not change here