Allow FunctionResultContent pass-through when CallId matches

[Copilot]

• Understand the problem: FunctionInvokingChatClient.CreateResponseMessages should reuse FunctionResultContent returned by the function if the CallId matches
• Implement the change in FunctionInvokingChatClient.cs at line 1230
• Add tests to verify the new behavior
• Unseal FunctionCallContent and FunctionResultContent classes
• Update API baseline to reflect unsealed classes
• Add test validating that a derived FunctionResultContent type is propagated to the inner IChatClient
• Validate that the FunctionResultContent is the only one in the tool message
• Assert reference equality in tests
• Add streaming path tests for all new tests
• Obtain tool message from ChatResponse instead of capturing via callback
• Run tests to validate changes
• Code review fixes

Summary

This PR modifies FunctionInvokingChatClient.CreateResponseMessages to check if the function result is already a FunctionResultContent with a matching CallId. If so, it uses that instance directly instead of wrapping it in a new FunctionResultContent. This gives the AIFunction flexibility to create its own FunctionResultContent configured however it wants.

Additionally, this PR unseals FunctionCallContent and FunctionResultContent classes to allow derivation.

Changes:

1. Modified FunctionInvokingChatClient.CreateFunctionResultContent method to check if the result is a FunctionResultContent with a matching CallId and return it directly
2. Unsealed FunctionCallContent and FunctionResultContent classes to allow derivation
3. Updated API baseline files for the unsealed classes
4. Added tests with both non-streaming and streaming paths and reference equality assertions:
   • FunctionReturningFunctionResultContentWithMatchingCallId_UsesItDirectly: Verifies that when a function returns a FunctionResultContent with matching CallId, it is used directly (same reference)
   • FunctionReturningFunctionResultContentWithMismatchedCallId_WrapsIt: Verifies that when a function returns a FunctionResultContent with mismatched CallId, it is wrapped in a new FunctionResultContent (with the inner one reference-equal)
   • FunctionReturningDerivedFunctionResultContent_PropagatesInstanceToInnerClient: Verifies that a derived FunctionResultContent type is properly propagated to the wrapped IChatClient and is the only one in the tool message (same reference)

Original prompt

On FunctionInvokingChatClient.cs:1230-1230, Right now, FunctionInvokingChatClient.CreateResponseMessages wraps the result of the function in a new FunctionResultContent. If, however, the object returned by the function is already a FunctionResultContent, and if that FunctionResultContent's CallId matches the one it's supposed to be, the implementation should just use that returned instance rather than creating a new one. This gives the AIFunction flexibility to create its own FunctionResultContent configured however it wants.

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Microsoft Reviewers: Open in CodeFlow

[stephentoub]

@copilot also unseal FunctionCallContent and FunctionResultContent and add tests validating that an AIFunction can return a FunctionResultContent-derived type and that instance is what's propagated to the IChatClient wrapped by the FunctionInvokingChatClient.

[Copilot]

@copilot also unseal FunctionCallContent and FunctionResultContent and add tests validating that an AIFunction can return a FunctionResultContent-derived type and that instance is what's propagated to...

Done in 790f979. Unsealed both FunctionCallContent and FunctionResultContent, updated the API baseline file, and added the FunctionReturningDerivedFunctionResultContent_PropagatesInstanceToInnerClient test that verifies a derived FunctionResultContent type is properly propagated to the wrapped IChatClient.

[jozkee]

Otherwise, LGTM.

[Copilot]

Pull request overview

This PR updates FunctionInvokingChatClient so that it can re-use FunctionResultContent instances returned directly from functions when the CallId matches, enabling more flexible and customized function result handling. It also unseals FunctionCallContent and FunctionResultContent to allow derivation and adds tests and API baseline updates to validate and document the new behavior.

Changes:

• Update FunctionInvokingChatClient.CreateResponseMessages (via CreateFunctionResultContent) to short-circuit and return an existing FunctionResultContent when the function result is already a FunctionResultContent with a matching CallId.
• Unseal FunctionCallContent and FunctionResultContent to support derived content types, and update the AI abstractions API baseline accordingly.
• Add unit tests covering matching/mismatched CallId behavior and propagation of a derived FunctionResultContent type through the inner IChatClient, including ensuring only a single FunctionResultContent is present in the tool message.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs	Adds a conditional path in CreateFunctionResultContent to re-use an existing FunctionResultContent instance when the CallId matches, otherwise preserving the existing wrapping logic.
src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/FunctionCallContent.cs	Removes sealed from FunctionCallContent to allow inheritance while keeping existing behavior and API intact.
src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/FunctionResultContent.cs	Removes sealed from FunctionResultContent so it can be subclassed (e.g., to add custom properties) without changing its current public API surface.
src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json	Updates the API baseline to reflect that FunctionCallContent and FunctionResultContent are now unsealed classes.
test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/FunctionInvokingChatClientTests.cs	Adds tests verifying pass-through of matching FunctionResultContent, wrapping on mismatched CallId, and correct propagation of a derived FunctionResultContent to the inner client with only one tool result message.