.NET: Propagate FunctionResult.Metadata to AgentRole.Tool ChatMessageContent.Metadata

[gmtorres]

Motivation and Context

There is currently no way to propagate custom metadata from function invocation filters to OrchestrationResponseCallback. Right now AddFunctionCallResultToChatHistory discards FunctionResult.Metadata and it is not exposed to OrchestrationResponseCallback.

This enables scenarios where we want to consume user-defined metadata in invocation filters, such as function result token count ReductionFilter, exception handling, etc

Description

Pass resultContext.Context.Result.Metadata to the ChatMessageContent constructor in
AddFunctionCallResultToChatHistory, so that metadata set on FunctionResult during the filter pipeline flows through to
the chat history message and ultimately to OrchestrationResponseCallback.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

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[Copilot]

Pull request overview

This PR enables propagation of user defined FunctionResult.Metadata created or modified in auto function invocation filters into the ChatHistory tool message metadata, making it accessible to downstream consumers like OrchestrationResponseCallback.

Changes:

• Populate ChatMessageContent.Metadata for tool messages with AutoFunctionInvocationContext.Result.Metadata when adding function results to chat history.
• Add a unit test validating metadata flow from a filter set FunctionResult.Metadata to the resulting tool ChatMessageContent.Metadata.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
dotnet/src/InternalUtilities/connectors/AI/FunctionCalling/FunctionCallsProcessor.cs	Propagates FunctionResult.Metadata into the tool ChatMessageContent added to ChatHistory.
dotnet/src/SemanticKernel.UnitTests/Utilities/AIConnectors/FunctionCallsProcessorTests.cs	Adds coverage to verify function result metadata is preserved on the tool message in chat history.

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[github-actions]

Automated Code Review

Reviewers: 4 | Confidence: 91%

✓ Correctness

This PR propagates FunctionResult.Metadata to the ChatMessageContent added to chat history after function call execution. The implementation accesses resultContext.Context.Result.Metadata to pass as the metadata parameter to the ChatMessageContent constructor. The code is correct: Result is a non-nullable property on AutoFunctionInvocationContext (always initialized), Metadata is nullable IReadOnlyDictionary which the ChatMessageContent constructor accepts as nullable, and the test properly validates the round-trip through a filter that sets metadata on the FunctionResult. The change is minimal and well-tested.

✓ Security Reliability

This PR propagates FunctionResult.Metadata from function invocation results to the ChatMessageContent added to chat history. The change is minimal and safe. The metadata parameter on the ChatMessageContent constructor is nullable (IReadOnlyDictionary<string, object?>?), so null metadata in the error path (when ExecuteFunctionCallAsync catches an exception and the FunctionResult retains its initial null metadata) is handled gracefully. No injection risks, resource leaks, or unsafe deserialization are introduced. The metadata is user-controlled (set by function implementations or auto-invocation filters), so propagating it to chat history is an intentional and appropriate design choice. The test adequately verifies the new behavior by exercising a filter that sets custom metadata and asserting it appears on the tool message.

✓ Test Coverage

The PR adds metadata propagation from FunctionResult to ChatMessageContent in the tool message added to chat history. The test covers the key scenario where a filter sets metadata on the FunctionResult and verifies it appears on the resulting ChatMessageContent. The test is well-structured with meaningful assertions. However, there are two missing edge-case tests: (1) the default case where no filter modifies metadata (metadata should be null), and (2) the error/exception path where AddFunctionCallResultToChatHistory is also called but the FunctionResult has no metadata. These are not blocking since the null-metadata case is implicitly covered by all existing tests that don't set metadata, but an explicit null-metadata assertion would strengthen confidence.

✗ Design Approach

The single-line change propagates FunctionResult.Metadata to the ChatMessageContent that wraps the tool response, which is the intended behavior. However, the implementation has a subtle design flaw: by passing metadata to the ChatMessageContent constructor together with content, the metadata is inadvertently copied into the auto-created TextContent item inside Items. This happens because the Content property setter (called from the constructor after this.Metadata is already set) creates a new TextContent(metadata: this.Metadata). As a result, the function result metadata ends up on both message.Metadata and message.Items[0] (the TextContent), but not on message.Items[1] (the FunctionResultContent), which is the semantically correct carrier for function-invocation metadata. The fix is simple: construct the message without metadata (so the TextContent is created with null metadata), then assign message.Metadata separately. The test is well-structured and validates the right observable behavior.

Flagged Issues

• Passing metadata in the ChatMessageContent constructor causes the same metadata dictionary to be copied into the auto-created TextContent item (via the Content setter's new TextContent(metadata: this.Metadata) path). Function-result metadata is semantically tied to the function invocation, not to a text representation item. The correct approach is to set message.Metadata after construction, so the TextContent stays metadata-free while the message-level metadata still propagates correctly.

Suggestions

• Consider adding a test for the error/exception path (function throws) to verify that AddFunctionCallResultToChatHistory does not surface unexpected metadata on the tool message—currently the error path still flows through this method and will propagate whatever metadata exists on the FunctionResult at the time of failure.
• Consider adding a test that verifies ChatMessageContent.Metadata is null when no filter modifies the FunctionResult metadata (the default path), ensuring the change doesn't accidentally introduce non-null metadata where none existed before.

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Automated review by gmtorres's agents

[github-actions]

Passing metadata to the constructor causes the Content setter (called inside the constructor after this.Metadata is already set) to forward the same metadata to the auto-created TextContent item via new TextContent(metadata: this.Metadata). Function-result metadata doesn't belong on the text item. Assign Metadata after construction to avoid this leakage.

Suggested change

	var message = new ChatMessageContent(role: AuthorRole.Tool, content: resultContext.Result, metadata: resultContext.Context.Result.Metadata);
	var message = new ChatMessageContent(role: AuthorRole.Tool, content: resultContext.Result);
	message.Metadata = resultContext.Context.Result.Metadata;

[gmtorres]

Good catch, addressed

[github-actions]

The test only covers the case where metadata is explicitly set by a filter. Consider adding analogous test without the filter (or with a no-op filter) to assert that toolMessage.Metadata is null when no metadata is provided, validating the change doesn't regress default behavior.

Suggested change

[Fact]