Port ContextualFunctionProvider from SK

[westey-m]

Motivation and Context

#2448

Description

• Porting ContextualFunctionProvider from SK to AF.

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.

[SergeyMenshykh]

I wonder whether we should go with the more abstract name Tools instead of the more specific Functions.

[westey-m]

Yeah, I'm not convinced .Functions is right either. Want to bring it up as a discussion point with the team.

[Copilot]

Pull request overview

This PR ports the ContextualFunctionProvider from Semantic Kernel (SK) to the Agent Framework (AF), enabling RAG (Retrieval-Augmented Generation) on functions to identify the most relevant functions for a given context.

Key Changes:

• Introduced FunctionStore class for vectorizing and storing functions in a vector store
• Added ContextualFunctionProvider that performs vector searches to find relevant functions based on context
• Implemented comprehensive configuration options through ContextualFunctionProviderOptions and FunctionStoreOptions

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
dotnet/src/Microsoft.Agents.AI/Functions/FunctionStore.cs	Core internal class for storing and searching functions using vector similarity
dotnet/src/Microsoft.Agents.AI/Functions/FunctionStoreOptions.cs	Internal configuration options for function store customization
dotnet/src/Microsoft.Agents.AI/Functions/FunctionStoreLoggingExtensions.cs	Logging extension methods for function vectorization and search results
dotnet/src/Microsoft.Agents.AI/Functions/ContextualFunctionProvider.cs	Public AI context provider that uses vector search for function selection
dotnet/src/Microsoft.Agents.AI/Functions/ContextualFunctionProviderOptions.cs	Public configuration options for contextual function provider
dotnet/tests/Microsoft.Agents.AI.UnitTests/Functions/FunctionStoreTests.cs	Unit tests for FunctionStore covering constructor validation, save, and search operations
dotnet/tests/Microsoft.Agents.AI.UnitTests/Functions/ContextualFunctionProviderTests.cs	Comprehensive unit tests for ContextualFunctionProvider including context building and function retrieval

[westey-m]

These need to be serialized into the AIContextProvider state

[westey-m]

@copilot, please add serialization and deserialization code, that stores the recent messages in serialized state.
See the TextSearchProvider as an example.
Also add unit tests for this behavior.

[westey-m]

This should check for an exception in the context before adding messages to the queue.

[westey-m]

@copilot, update the code here so that that if the context has a non-null exception, it doesn't add messages to the recent messages list.

[Copilot]

@westey-m I've opened a new pull request, #2600, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

@westey-m I've opened a new pull request, #2601, to work on those changes. Once the pull request is ready, I'll request review from you.