.NET: [BREAKING] Add support for multiple AIContextProviders on a ChatClientAgent

[westey-m]

Motivation and Context

This is one PR in a sequence to enable having mutiple AIContextProviders as a pipeline directly on the agent.

Description

• Add support for passing multiple AIContextProviders directly to a ChatClientAgent
• Add key checking to stop users from accidentally using the same key twice and overwriting state.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

This PR introduces breaking changes to enable multiple AIContextProviders on a ChatClientAgent, replacing the single AIContextProvider property with an AIContextProviders collection. This enhancement allows agents to compose context from multiple sources in a pipeline pattern, where each provider receives and can augment the accumulated context from previous providers.

Changes:

• Changed ChatClientAgentOptions.AIContextProvider from single instance to AIContextProviders collection (IEnumerable)
• Added StateKey validation to prevent multiple providers from using the same key and overwriting each other's session state
• Implemented sequential invocation of multiple providers with context accumulation
• Updated all extension methods, samples, and tests to use the new collection-based API

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentOptions.cs	Changed AIContextProvider property from single to collection, updated Clone method
dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs	Added StateKey validation, provider collection property, sequential invocation logic, and runtime validation for overrides
dotnet/src/Microsoft.Agents.AI.OpenAI/Extensions/OpenAIAssistantClientExtensions.cs	Updated to use AIContextProviders collection
dotnet/src/Microsoft.Agents.AI.AzureAI/AzureAIProjectChatClientExtensions.cs	Updated to use AIContextProviders collection
dotnet/src/Microsoft.Agents.AI.AzureAI.Persistent/PersistentAgentsClientExtensions.cs	Updated to use AIContextProviders collection
dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentTests.cs	Added comprehensive tests for StateKey validation, multiple provider invocation, and helper test classes
dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentOptionsTests.cs	Updated tests to use AIContextProviders collection
dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgent_BackgroundResponsesTests.cs	Updated tests to use AIContextProviders collection syntax
dotnet/tests/Microsoft.Agents.AI.AzureAI.UnitTests/AzureAIProjectChatClientExtensionsTests.cs	Updated test to use AIContextProviders collection
dotnet/samples/GettingStarted/Agents/Agent_Step20_AdditionalAIContext/Program.cs	Removed AggregatingAIContextProvider class, updated to use built-in multiple provider support
dotnet/samples/GettingStarted/AgentWithRAG/AgentWithRAG_Step01_BasicTextRAG/Program.cs	Updated to use AIContextProviders collection
dotnet/samples/GettingStarted/AgentWithRAG/AgentWithRAG_Step02_CustomVectorStoreRAG/Program.cs	Updated to use AIContextProviders collection
dotnet/samples/GettingStarted/AgentWithRAG/AgentWithRAG_Step03_CustomRAGDataSource/Program.cs	Updated to use AIContextProviders collection
dotnet/samples/GettingStarted/AgentWithMemory/AgentWithMemory_Step01_ChatHistoryMemory/Program.cs	Updated to use AIContextProviders collection
dotnet/samples/GettingStarted/AgentWithMemory/AgentWithMemory_Step02_MemoryUsingMem0/Program.cs	Updated to use AIContextProviders collection
dotnet/samples/GettingStarted/AgentWithMemory/AgentWithMemory_Step03_CustomMemory/Program.cs	Updated to use AIContextProviders collection

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 5 comments.